Mother Earth has been a concept for a long time but the scientific concept of life being self regulating was largely coined by the late Dr. James Lovelock in a theory known as the Gaia Hypothesis. This hypothesis captured life’s nature to recover and the interconnected system between organisms. Although later combated or maybe better complicated by the Medea hypothesis theorised by Professor Peter Ward and the popular book, The Selfish Gene by Dr Richard Dawkins. These two theories encapsulate the complex nature of life itself and the many mass extinction events caused by species in that fight for life and reproduction.
Survival is argued as not altruistic regardless if competing with members of your own species or another. There is a constant battle not just between predator and prey but between competitors for resources such as space. This battle is not just found in the animal world though, plants fight for space and use a variety of mechanisms to do this.
But how does this effect us in the aquarium hobby? Just by the selfish nature of organisms we can’t look at each organism providing a role, that’s not how nature works and it ignores that species provide multiple interactions. Plants don’t just photosynthesise but they constantly respire and also utilise minerals within the water. These plants might then compete with each other and maybe a fish for a variety of these resources. To compete with plants many develop methods to block out light but in that competition for space other methods might be utilised, plants like many other organisms potentially utilise chemical warfare.
Within animals when people think about purposes particularly pests they might not just interact as ideally wanted, loaches that feed on snails might take smaller fishes.
In the aquarium I feel we have to balance this constant battle. Everything using oxygen, feeding on nutrients and space.
While I’ve provided no citations it’s more a food for thought short communication essay.
Within the aquarium hobby there are not many cases of husbandry that are used to improve a fishes appearance beyond maybe a red enhancing diet or just general good care.
It’s a little difficult from any of the grooming you can do with other animals, we can provide enrichment and exercise but again it’s not quite the same. Although in the goldfish hobby there are definitely quite a few practices aimed at improving a fishes condition from certain shaped containers to lighting.
The topic for this article is about lighting, more specifically whatever maybe called natural lighting as do we even know what we are referring to by that? The use of lighting is not just used within goldfish but also Asian arowana, discus maybe to a lesser extent.
Regarding discus just to get it out of the way, their colouration is dictated easily by the brightness of the setup so not strictly lighting but that is a massive contributing factor. In a dark setup the fishes will change to a darker patterning, if possible they will produce those solid bars of pigmentation from dorsal to ventral. In wilds such as S. tarzoo they go much darker as in the photo below:
Yet in a much lighter setup you can see a lot more of the fishes beautiful colours.
This is not just strict to wild discus who likely use their chameleon abilities to communicate and blend in with their environment, it is found in domestics too. There is one issue there, there are many varieties, the most popular being the pigeon bloods who cannot colour change as quickly. These varieties instead develop what is known as peppering, black spots on the body and as while they can disappear with brighter lighting it takes a lot more effort and time. Maybe this is the answer for anyone wondering why discus aquariums look the way they do?
This is a difficult topic to research scientifically though, mainly because it effects the hobbyist and really will lack any funding to support research. There is a little though in some species and through the review of Leclercq et al. (2010) we know that UV light particularly UVB contributes to colour changes in many fishes followed by the background unlike discus. UVB is additionally the spectrum of light that causes tanning in humans, similar to goldfishes where there is a predisposition to black pigmentation either get a higher intensity of black pigmentation or it grows.
The colour changes could be a result of UV protection given there are levels that penetrate depending on the water turbidity and location (Mueller & Neuhauss, 2014). While maybe there is other causes to this change in colouration? Either way it is utilised quite a bit in the hobby.
So why the title? I could get away with it with just mentioning goldfish but tanning of fishes is well known with the dragon fish, the Asian arowana, Scleropages formosus to produce intense deeper colouration.
So how is it done? In some countries or in the case of goldfish having ponds outside will do the job, natural sunlight not passing through glass but obviously this is not possible for many of us. UVB being the likely main aspect of lighting that we need to aim for lighting needs to go out of the realm of fishkeeping and into herpetoculture. In the care of reptiles UVB lights are quite common and these should do the job, what I cannot recommend is how much and how little to use and I feel personal experimentation would be important. Bare in mind reptile UVB lighting requires replacing every 6-9 months as it only emits UVB for so long.
I have experimented with a variety of lights and with goldfish found nothing compared, confirming UVB’s importance in my personal opinion. I have found fluorescents although producing no UVB much much better then LED’s apart from in the case of dealing with fishes like discus that want brightness rather then certain aspects of the spectrum.
Considerations are certainly needed, it would not be ideal for the lighting to be on constantly so not to mess with the fishes circadian rhythm. Another aspect is there is too much UVB and fishes might feel they do not want to be exposed to bright light constantly, I would certainly give them refuge from the light in terms of some cover that should they want to they can retreat to.
There is no doubt goldfish, Carassius auratus is one of the most adaptable fish species. While the parent species being either/or the Prussian carp, C. gibelio or the Crucian carp, C. carassius are proven without a doubt to adapt to a range of climates the goldfish on the other hand is treated as the sensitive child. Well, not all goldfish but this is very much a cherry picking of different varieties thrown into hardy or not.
First lets split the goldfish up:
Single tails
Common/hibuna: This is the typical goldfish with the short single caudal fin.
Comet: Displays a more elongate caudal fin that might be more ribbon shaped.
Shubunkin: This is a variety that is split into multiple different subvarieties depending on caudal fin type. The London shubunkin has a shorter caudal fin, the common body and tail shape. The Japanese shubunkin has that comet caudal fin shape. The Bristol shubunkin being unique with a large elongate but heart shaped caudal fin that holds it’s height and shape. The difference between the shubunkin and the first two is the calico patterning, black, red, orange and blue.
Tamasaba and sabao, shorter ryukin shaped goldfish with white and red patterning originally bred by Japanese koi breeders. The Tamasaba has the longer caudal fin.
Nymph, not so much a variety but a undesirable mutation of the double tailed varieties where a number of single tailed individuals are produced.
Double tailed, this is produced by a duplication event (Abe et al., 2014).
Wakin: Very similar to the common goldfish but with a double tail. Not to be confused with mutations in commons, comets and shubunkin resulting in a double tail, I have seen full to partial splits at least 3 times, the wakin seems to have more of an arch to the spine at the back.
Jikin: Similar to the wakin but deeper bodied, seems to lack that arching and with more of a flower shaped caudal fin. It is strictly red and white, ideally with 13 points of red but this is produced by certain methods.
Fantail: The most famous and varies on quality or how much it matches the standards. This variety by standard should be deeper bodied but has a short heart shaped caudal fin.
Oranda: There are multiple subvarieties from goosehead to lionhead oranda, this variety is a deep bodied fish with fatty growths covering the head or the top of the head. Caudal fin shape also varies depending on standard and variety from a straight long veiltail to a short heart shaped caudal fin.
Ryukin: An extreme deep bodied and described by the GSGB (Goldfish Society of the British Isles) as having a bulldog like appearance, it has a hump behind the head resulting in it’s unusual appearance. Despite the name it is not originally Japanese as having originated from China arriving via the Ryukyu Islands, quite a few varieties often thought of as Japanese have Chinese origins.
Lionhead: As of recent an uncommon variety, most sold under this name are in fact low quality oranda. It should have a large fatty head growth like the oranda but lack a dorsal fin and have a straighter back.
Ranchu: There are multiple varieties of this, the original Japanese ranchu is known as the top view ranchu, uncommon outside certain exporters. Like most true Japanese fish to be judged from above. Lacks a dorsal fin with a nice smooth arched back, short caudal fin and an attractive fatty head growth. Side view ranchu are common in the trade.
Tosakin: A rare variety in the UK, very similar to a fantail but has a long caudal fin that is spread out in a butterfly shape to be viewed from above. Reached close to extinction in Japan but is making a recovery.
Izumo nankin: A rare variety, similar to the ranchu in it’s deeper body but lacks any head growth. Red and white patterning in a desired pattern.
Veiltail: Uncommon outside the show scene, has a broad, lacking that forking long caudal fin otherwise similar to the fantail.
Moor: A telescope eyed variety, it generally in the UK has a veiltailed caudal fin to be standard and must have more triangular eyes.
Globe eye: Similar to the moor in being a telescope eye but the eyes are rounded, the tail can be short or long but generally rounded and forked. Demekins do somewhat fall under this but are almost like a cross between the ryukin and globe eye.
I didn’t list these varieties for no reason, body shape is extremely diverse between each and therefore the split only means a difference in whether there is two or one caudal fin. Fancy usually refers to any goldfish but the comet, shubunkin and common which if you get what I mean it really means very little as a term.
There is a long history of goldfish’s being kept and bred outside in not just Japan and China; but also Thailand, Java, the UK and the USA. It is not difficult to find this in societies alternatively in a greenhouse.
I myself have kept a variety of fancies outside year round but it requires serious thought.
What benefits could keeping goldfish outside have?
The major obvious one is colouration, natural lighting perhaps it’s the UVB really enhances black pigmentation (melanin) in goldfish or preventing any loss. Any green water encourages red colouration.
Potentially more natural food sources, many insects and invertebrates naturally become introduced to ponds.
Natural seasonal cycles like they would have experienced as a wild species, it gives them a period of rest. It is obvious how seasonal these fishes are in the fact they spawn with seasonal temperature ques.
The opportunity and ease of providing more space, ponds are generally cheaper then aquariums. This can allow for much more enrichment.
Considerations
Goldfish still need water changes and filtration in a pond regardless of plants or setup.
Only add fishes to ponds in the warmer months, May to September (based on UK temperatures), ideally 15-18c or above giving them plenty of time to adapt to temperature drops later on in the year and avoiding sudden frosts.
Over winter and when temperatures drop the fishes will have a reduced appetite and reduced metabolism so feeding is best reduced slowly to a stop in winter to prevent any rotting of uneaten food. When temperatures increase again the fish can be fed again. Water changes aren’t required when the fishes have such a drop of metabolism.
Goldfish are susceptible to predators so netting or grids above the pond is a must.
While goldfish are more then capable of going anaerobic during periods of cold extreme cold resulting in a deep and thick ice layer should be considered in countries where this occurs. This might mean any fishes being taken inside between September to May. Depth of pond is also important as the bottom will create a refuge for the fishes, shallow is much better for body shape but the temperature will drop much more rapidly.
Any fishes displaying swim bladder disorders should be removed and kept inside as the heat or cold can damage any floating fish.
In summer a good filter should create enough aeration and goldfish can gulp but an air pump or fountain would be important to maintain oxygen levels.
You can see it’s not so simple but it doesn’t mean it’s bad to keep them outside. The importance of natural cycles is potentially very understudied and underrated within the aquarium hobby. Potentially it could even lead to a longer lifespan and healthier fishes but we don’t really know?
Both goldfish considered fancy and not are both farmed in hotter climates then ours in the UK so there isn’t so much logic behind their perceived variance sensitivity excluding the limited gene pool of some.
References
Abe, G., Lee, S. H., Chang, M., Liu, S. C., Tsai, H. Y., & Ota, K. G. (2014). The origin of the bifurcated axial skeletal system in the twin-tail goldfish. Nature communications, 5(1), 3360.
Recently it seems Epistylis has become a trigger word whenever a fish is displaying spots on the body where previously white spot, Ichthyophthirius multifiliis would have previously been the diagnosis. While I feel we are often misdiagnosing fishes due to lack of awareness of all the pathogens out there Epistylis is definitely one of the largest myths.
To put it simply, Epistylis is a genus 200 spp. ciliate protozoa that can parasitise on fishes often as a secondary pathogen. It is but appears as a little round ciliated bulb on a stalk, much like Vorticella or rotifers (Wu et al., 2021). In fact though the pathology of the genus in regards to parasitism on fishes has little references to how it looks from the naked eye. Instead the accompanying primary infection e.g. Aeromonas sp. displaying red spots/lesions (Fig 1) but Epistylis niagarae has been suggested to cause scale erosion (Ksepka & Bullard, 2021; Chapman et al., 1976), there is no mention in the literature of Epistylis displaying spots on the body (Pádua et al., 2016).
Figure 1: Red Spot disease caused by Aerosomas possibly with a secondary Epistylis infection as published by Ksepka & Bullard (2021).
Instead it seems Epistylis is most accurately identified using a microscope due to it’s distinctive appearance. In Rahmati-Holasoo et al. (2023) it discusses the attachment of Lernaea to the host fish and displays clear images of the common, Epistylis wuhanensis.
Figure 2: A clear infection of Epistylis published in Rahmati-Holasoo et al. (2023).
It seems that Epistylis is not reported as the rapid killer although the Aerosomas infections could have been the cause, unlike many misconceptions (Chapman et al., 1976).
Is it white spot then?
I can’t say it is, I can say though a microscope should be needed to be sure. I have seen many cysts on fishes and without a microscope it’s just identifying that it’s a lump. Tapeworm cysts I have identified though largely using a microscope but they are larger and do not respond to treatment.
Without a microscope there is a lot of diagnosis going blindly in and even then. There are many resources for identifying fish parasites using microscopy, it’s important though to remember that not all pathogens have been discovered and there are exceptions. Many similar taxa usually can be treated by the same compounds.
Why does it matter?
From my understanding although Epistylis is generally a secondary parasite and not the cause of the infection, it’s opportunistic it usually is susceptible to the same treatments as white spot. Over use of treatments particularly when not targeting the parasite can lead to resistance and I do wonder if that is sometimes what we are seeing. This is more an element of fact checking and should you trust your information sources? They can claim science but do they cite their sources or read theirs? Experience only goes so far but experience doesn’t change what species is what.
References:
Chapman, W. R., Harris, F. A., & Miller, R. W. (1976). Incidence and seasonal variations of Epistylis among fishes in North Carolina reservoirs. In Proceeding of the Annual Conference of Southeastern Association of Game and Fish Commissioners (Vol. 30, pp. 269-275).
Ksepka, S. P., & Bullard, S. A. (2021). Morphology, phylogenetics and pathology of “red sore disease”(coinfection by Epistylis cf. wuhanensis and Aeromonas hydrophila) on sportfishes from reservoirs in the South‐Eastern United States. Journal of Fish Diseases, 44(5), 541-551.
Pádua, S. B. D., Martins, M. L., Valladão, G. M. R., Utz, L., Zara, F. J., Ishikawa, M. M., & Belo, M. A. D. A. (2016). Host-parasite relationship during Epistylis sp.(Ciliophora: Epistylididae) infestation in farmed cichlid and pimelodid fish. Pesquisa Agropecuária Brasileira, 51, 520-526.
Rahmati-Holasoo, H., Marandi, A., Shokrpoor, S., Goodarzi, T., Ziafati Kafi, Z., Ashrafi Tamai, I., & Ebrahimzadeh Mousavi, H. (2023). Clinico-histopathological and phylogenetic analysis of protozoan epibiont Epistylis wuhanensis associated with crustacean parasite Lernaea cyprinacea from ornamental fish in Iran. Scientific Reports, 13(1), 14065.
Rogers, W. A. (1971). Disease in fish due to the protozoan Epistylis (Ciliata: Peritricha) in the southeastern US. In Proc. 25th Ann. Conf. Southeastern Assoc. Game and Fish Comm., 1971 (pp. 493-496).
Wu, T., Li, Y., Zhang, T., Hou, J., Mu, C., Warren, A., & Lu, B. (2021). Morphology and molecular phylogeny of three Epistylis species found in freshwater habitats in China, including the description of E. foissneri n. sp.(Ciliophora, Peritrichia). European Journal of Protistology, 78, 125767.
Biological/Biochemical Oxygen Demand (BOD) is a topic we never discuss in the hobby, it refers to largely to the amount of oxygen that aerobic microorganisms use to remove or process waste (Brenniman, 1999) and are directly connected with oxygen saturation and nitrate concentration (Alam et al., 2020).
In a way the hobby talks so little about decomposition focusing on other aspects of nutrient cycling. For a fishkeeper that water changes, siphons and leaves little to no waste or items decaying in the aquarium it might not be of concern.
Botanicals and planted tanks are very popular as of recent with people reaching for some idea of nature they feel they have lost, natural or not. Both of these setups can allow for the trapping of waste where siphoning is not possible or limited. One solution is reduced stocking but definitely keeping fishes adapted for low oxygen saturations is a great solution such as airbreathers.
Decomposition of material such as decaying plants or botanicals involve bacteria, protozoa and other microorganism’s. It’s not just these as an introduction of nutrients but also anything that can be used as a nutrient source for bacteria, I find particularly sugars and carbohydrates. We can split them between aerobic (With oxygen) and anaerobic (without oxygen), anaerobic is another topic here but it does involve the production of other compounds. Just because there is a thick layer of substrate it doesn’t mean it is anaerobic particularly with the presence of plant roots that encourage oxygenation. We also don’t know the rate of either and this will depend on a variety of factors.
These microorganisms are more then capable of competing with fishes for oxygen and the rate will depend on multiple conditions (Nolan, 1996; El-Moghazy & El-Morsy, 2017). Microorganisms can proliferate much faster then fishes so can quickly adapt and increase to those higher nutrient levels.
The issue is that we can barely measure BOD but we can measure oxygen saturation. This means it is difficult to experiment the BOD within any aquarium so we do have to make assumptions.
Most of these are purely assumptions and ideas based on previous knowledge as it’s not so much a topic that the literature will look into. It’s also something fishkeepers certainly need to be thinking about or considering particularly for heavily stocked tanks or fishes who uptake a lot of oxygen.
Temperature, oxygen saturation and decomposition rate
It is a well known effect that as temperature increases oxygen saturation in turn decreases although when thinking about decomposition this increases as microbial decomposers can proliferate at a much faster rate and consume their resources further. This could result in further BOD when there are already low levels (El-Moghazy & El-Morsy, 2017).
Generally it’s better safe then sorry so removing detritus that has built up in the tank and within the filter. Decomposers are probably only providing a benefit maybe for plants but for fishes in many aspects discussed previously they are not of benefit. Any botanicals or high nutrient imputs should be added gradually over time so not to unload a lot of nutrients into the aquarium or when decaying again as much nutrients for these microbes and reducing oxygen saturation.
While we don’t have values and honestly, there is no way of doing that as every aquarium is difficult it’s difficult to predict.
References
Alam, M. S., Han, B., Gregg, A., & Pichtel, J. (2020). Nitrate and biochemical oxygen demand change in a typical Midwest stream in the past two decades. H2Open Journal, 3(1), 519-537.
Brenniman, G. R. (1999). Biochemical oxygen demand. Environmental Geology. Encyclopedia of Earth Science. Springer, Dordrecht. https://doi. org/10.1007/1-4020-4494-1_34.
El-Moghazy, M. M., & El-Morsy, A. M. (2017). Effect of water aquaria changes on growth performance of Nile tilapia Oreochromis niloticus and the relationship between bacterial load and biological oxygen demand. International Journal of Fisheries and Aquatic Studies, 5(3), 341-349.
Nolan, C. (1996). Ventilation rates for carassius auratus during changes in dissolved oxygen.
This is the big question, what do you base a fish diet on?
Fish meal is the most common but has come with many questions based on sustainability, but regarding sustainability this can be a little more complex regarding shifting impact (Ghamkar & Hicks, 2020). Therefore there is the question of what gives the most nutrition?
Žák et al. (2023) has been one of the most enlightening papers published in the last few years. This research and other previous research has inferred that for invertivores and insectivores but it is eye opening to apply elsewhere. Digestibility of fish meals does vary depending on the taxa and likely what they feed on in the wild, Cyprinids largely feeding on invertebrates and lacking a stomach struggle to process fishes whereas Tilapia, a cichlid that likely is very generalist even feeding on fishes processes fish much better (Hua & Bureau, 2010). The other aspect is that fish meal can be difficult to extract phosphorus and calcium for fishes that do not naturally feed on fishes (Žák et al. 2023). We can apply this knowledge further?
So maybe fishes isn’t ideal, most of the fishes we keep don’t eat fishes. But what about invertebrates? There is no denying most of the scientific literature focuses on fishes that likely feed on krill being marine fishes or very much generalist omnivores. So, I’m not sure I can find anything regarding that, any environmental impact would be similar to fish meals, talking from personal experience krill and marine mysis does come with a lot of bycatch.
Although insect meals are definitely interesting, there are many more nutritional aspects to consider. While much of the focus from the customer is into protein, vitamins and minerals are vital for fishes. Vitamin b12 is a popular vitamin to mention due to origins, insects contain little to higher amounts but also depends on what they have been fed (Schmidt et al., 2019) although there is a lot of deceptively high amounts in all insects from pseudovitamin b12 such as contained in algaes. Chitin might cause an issue in some fishes, in my experience largely it’s whether an invertebrate is processed or not rather then causing issues with digestion.
There is no strict one is better then the other like many things as it has multiple aspects to the topic (Terova et al., 2021). Given the literature mentioned think about what the fishes eat in the wild and are they piscivores, feeding on fishes naturally.
It is well know how diet influences gut biota, not just are species adapted through evolution regarding enzymes to a specific diet but also symbiotically with bacteria allowing some items to be digested better then others. It’s not just that simple either but like with humans the introduction or even encouragement of certain biota in the gut can effect health in general (Ringø et al., 2016). With humans we are now discussing the gut brain axis but it is becoming a topic within fishes as well where the presence, lack or amount of certain biota influences how the brain functions in fishes and the prevalence of disease (Butt & Volkoff, 2019).
The Question of Soya
The use of crops like soya has been mentioned of reducing the impact of animal based meals yet increases demand for water up 63%, land 81% and phosphorus 83%, phosphorus itself is a finite resource but a vital fertiliser (Malcorps et al., 2019). There are other aspects of soya and I think it’s best to mention most if any fishes I research and this is largely Loricariids do not consume anything similar, cereal crops are very fibrous and difficult to digest which is different from the allochthonous sources they generally feed on.
While regarding short term use to certain volumes could replace other meals such as insect or fish (Howlader et al., 2023; Arriaga-Hernández et al., 2021). Yet the use of soya has been associated with a negative effects on growth (Pang et al., 2023). Many of these studies do not look into fishes even similar to what we keep, for discus (Symphysodon) beyond 30% replacement of other meals resulted in reduced growth rate (Chong et al., 2003).
Forgetting algivores?
Algivores or anything feeding on anything similar are not represented or thought about by the fishkeeper often, yet we keep so many of them. Similar information to the above definitely applies regarding how fishes are adapted through evolution to what they feed on in the wild. But could these other meals be of use? There is definitely a lack of studies looking into aquaculture, yet for an algivore just one species of algae the replacement of these traditional meals can produce the same results (Vucko et al., 2017), imagine using other algaes and a diversity of algaes?
References
Arriaga-Hernández, D., Hernández, C., Martínez-Montaño, E., Ibarra-Castro, L., Lizárraga-Velázquez, E., Leyva-López, N., & Chávez-Sánchez, M. C. (2021). Fish meal replacement by soybean products in aquaculture feeds for white snook, Centropomus viridis: Effect on growth, diet digestibility, and digestive capacity. Aquaculture, 530, 735823.
Butt, R. L., & Volkoff, H. (2019). Gut microbiota and energy homeostasis in fish. Frontiers in endocrinology, 10, 9.
Chong, A., Hashim, R., & Ali, A. B. (2003). Assessment of soybean meal in diets for discus (Symphysodon aequifasciata HECKEL) farming through a fishmeal replacement study. Aquaculture Research, 34(11), 913-922.
Ghamkhar, R., & Hicks, A. (2020). Comparative environmental impact assessment of aquafeed production: Sustainability implications of forage fish meal and oil free diets. Resources, Conservation and Recycling, 161, 104849.
Howlader, S., Sumi, K. R., Sarkar, S., Billah, S. M., Ali, M. L., Howlader, J., & Shahjahan, M. (2023). Effects of dietary replacement of fish meal by soybean meal on growth, feed utilization, and health condition of stinging catfish, Heteropneustes fossilis. Saudi Journal of Biological Sciences, 30(3), 103601.
Hua, K., & Bureau, D. P. (2010). Quantification of differences in digestibility of phosphorus among cyprinids, cichlids, and salmonids through a mathematical modelling approach. Aquaculture, 308(3-4), 152-158.
Malcorps, W., Kok, B., van ‘t Land, M., Fritz, M., van Doren, D., Servin, K., van der Heijden, P., plamer, R., Auchterlonie, N. A., Rietkerk, M., Santos, M. J. & Davies, S. J. (2019). The sustainability conundrum of fishmeal substitution by plant ingredients in shrimp feeds. Sustainability, 11(4), 1212.
Pang, A., Xin, Y., Xie, R., Wang, Z., Zhang, W., & Tan, B. (2023). Differential analysis of fish meal substitution with two soybean meals on juvenile pearl gentian grouper. Frontiers in Marine Science, 10, 1170033.
Ringø, E. Z. Z. V., Zhou, Z., Vecino, J. G., Wadsworth, S., Romero, J., Krogdahl, Å., Olden, R. E., Dimitroglou, A., Foey, Davies, S., Owen, M., Lauzon, H. L., Martinsen, L. L., De Schryver, P., Bossier, P., Sperstad, S. & Merrifield, D. L. (2016). Effect of dietary components on the gut microbiota of aquatic animals. A never‐ending story?. Aquaculture nutrition, 22(2), 219-282.
Schmidt, A., Call, L. M., Macheiner, L., & Mayer, H. K. (2019). Determination of vitamin B12 in four edible insect species by immunoaffinity and ultra-high performance liquid chromatography. Food chemistry, 281, 124-129.
Terova, G., Gini, E., Gasco, L., Moroni, F., Antonini, M., & Rimoldi, S. (2021). Effects of full replacement of dietary fishmeal with insect meal from Tenebrio molitor on rainbow trout gut and skin microbiota. Journal of Animal Science and Biotechnology, 12(1), 1-14.
Vucko, M. J., Cole, A. J., Moorhead, J. A., Pit, J., & de Nys, R. (2017). The freshwater macroalga Oedogonium intermedium can meet the nutritional requirements of the herbivorous fish Ancistrus cirrhosus. Algal research, 27, 21-31.
Žák, J., Roy, K., Dyková, I., Mráz, J., & Reichard, M. (2022). Starter feed for carnivorous species as a practical replacement of bloodworms for a vertebrate model organism in ageing, the turquoise killifish Nothobranchius furzeri. Journal of Fish Biology, 100(4), 894-908.
You’ve seen these growths, little white hairy tufts but what are they?
I asked this question when I first saw these so I put them under the microscope. Sadly the images of that are soo blurry.
But what do I think is here:
Vorticella
Bryozoa
Rotifers
Which is it then? Well definitely I have seen Vorticella, these look like little springy balloons under the microscopes. The other organisms I have seen could be either Bryozoans or Rotifers and I have definitely seen people with great Bryozoan colonies compared to this.
What is the cause?
These organisms are all filter feeders. These seem to really bloom to a high suspended sediment load so it is logical why these organisms are here. Like anything they are indicator species particularly when on the glass. I personally find they grow particularly well when using botanicals but as do biofilms so likely a lot of bacterial load in the water too.
What can I do?
Reduce the amount of sediment load so maybe using less botanicals in future? It’s difficult to say entirely.
As with every organism fishes do experience diseases and can play hosts for pathogens (some fish could be considered pathogens e.g. Vandellia cirrhosa (candiru catfish)). For the fishes and the fishkeeper it is an arms race of immune systems and treatments against the adaptability and damage to the host. This can be discussed as part of the red queen hypothesis (Van Valen, 1973), as a never ending feedback cycle, without the constant adaptation a species will go extinct.
I, the editor will clearly state that I am not a fish pathologist and this article, I am an evolutionary biologist/ichthyologist although this has given me an understanding into aspects of evolutionary pathology. Having worked in the aquarium trade I have additionally experienced a wide range of different pathogens. I will also state decisions regarding discussion the diseases as a result because I feel many fishkeepers have misunderstood fish pathology, there aren’t many hobbyists with that in their background I assume is the reason why.
Right now lets look a bit into pathogens.
Host specificity
While it is quite common knowledge that pathogens within humans or mammals can be very specific this is the same for fishes. There will be several reasons for this:
The evolutionary mechanisms to actually become a host require a variety of adaptations and some might be very specific. For example for viruses and bacteria they will have to have the correct proteins to enter cells (Cohen, 2016; A great paper introducing how viruses function). Pathogens might require the presence of specific tissues, this could be why there have been no proven cases of Lymphocytis in catfishes (siluriformes), salmonids and carp as these clades are very close and possibly lack the effected tissues.
Simply the environment might not be suitable for transmission between individuals, maybe the salinity is too high or the temperature is out of range.
The easiest way to assume is to look half at evolutionary distance, the more distant species are from each other the less likely transmission will occur. Additionally the pathogens of marine fishes are less likely to be able to survive and cause disease in freshwater and vice versa.
The fishes weaponry against pathogens.
This is very difficult to generalise given how many fishes there are and there is a lot of convergence with other organisms.
The first barrier, the skin, the scales and slime coat in general prevent or reduce access of pathogens to the internal environment where they can cause damage.
The slime coat, other then a physical barrier the skin contains many goblet cells which secretes many antimicrobial compounds such as proteases and lysozymes (Dash et al., 2018). These destroy and damage microbial pathogens and even parasitic pathogens. There is also the potential that the slime coat contains many beneficial microbes who help aid in that defence against any that become pathogenic. There is the possibility that fishes shed their slime coat to dislodge pathogens on their skin/scales or in the slime coat but I cannot find any evidence in the literature.
The immune system, this part of biology is probably the most complex and it is very species specific. So rather then me explain it very poorly I will link a very good, recent review paper on the topic https://www.mdpi.com/2410-3888/8/2/93
The latest science
There is a lot of research as of recent looking into how a microbial ecosystem in the gut and over the surfaces of fishes aid in protection against disease (Chu et al., 2014; D’Alvise et al., 2013). This can be influenced by the environment where poor water quality can change the balance, where a bacteria or fungus previously managed by the immune system and other pathogens can cause disease (Bentzon-Tilla et al., 2016). A major cause of tipping this balance is antibiotics and therefore, antibiotic resistance, this also limits ability to use antibiotics for more concerning bacteria (de Bruijn et al., 2018).
The balance of treatment
Regardless of what treatment I cannot think of one which doesn’t have a biological effect. In my first pharmacology lecture during my undergraduate degree the lecturer stated all treatments should be understood to not just effect the target tissue, they will travel throughout the body where they can. We are very limited within the aquarium trade of what we can use and it should be understood that there might be undesired long term consequences of any treatment e.g. formalin and formaldehyde are carcinogens yet very effective on protozoa. Antibiotic resistance is a real risk with their use hence strict UK regulations.
So this brings me onto my final point:
To diagnose or not to diagnose
Fishes can host many pathogens, some more common then others. They are extremely diverse and there are many more species then vets that do 5 years training normally handle, like 10-100x more species. A fish pathologist might do 3-4 years undergraduate training, 1-2 years masters training and maybe 3-6 years PhD training, just to understand maybe a set of bacteria, fungi, parasites etc. Or what most commonly hosts a particular taxa of fishes. It’s not a simple topic.
Even with identifying fishes I see the most common species misidentified, let alone pathogens of which many need to be seen under the microscope. That access to the microscope is half of the issues, most fishkeepers outside the koi world don’t own one. And I dare say if many did, can they identify what they are seeing? And it’s great if you can but then most bacteria, viruses can’t be seen using that method. For fishes it’s not so simple to do a biopsy. What makes me really think about this topic is the misdiagnosis of Epistylis, the literature diagnoses it very differently to the hobby (Valladao et al., 2015; Wang et al., 2017; Wu et al., 2021; Ksepka & Bullard, 2021) and I am not entirely sure where the myth that Epistylis can be confused with white spot started but it’s rather frustrating. From all the literature I cited there it can’t be really diagnosed using the naked eye. I am not a pathologist but I think maybe this is more a story of fact checking because a quick read of the literature tells another story.
There are a lot more diseases and pathogens then we even know as a hobby and sometimes they can appear in a wide diversity of forms e.g. Dermocystidium. There isn’t going to be a set 5-10 most common pathogens otherwise you could say other vertebrates you only need to know those few. I prefer to back off from fish pathology because honestly how easy is it to misdiagnose? Swim bladder disorders vs neurological disorders vs malnutrition. And with so little fact checking how much can be trust? There are great fish pathologists out there and a few fish specialist vets.
The other problem with diagnosis is, how much does the science even know about the fishes we keep? Individual species in our hobby often don’t hold the largest economic weight to warrant scientific study so I believe there is a lot we don’t know. Other then pathogens malnutrition is something that hasn’t particularly been looked at in tropical ornamental fishes.
Why does correct diagnosis matter?
If you want to use the correct treatment being the main reason you need to know what you are dealing with, without using one compound after another crossing them out as you go without thinking about the physiological impact on the fish. Treatment might need to be quick or need long multiple rounds of treatment. Thankfully there might be some overlap in some. For some diseases such as neurological or related to nutrition the cause or point might never be reached.
What do you recommend?
I don’t know, contacting a vet specialised in fishes is a great idea, if there is a laboratory or pathology service this can be another option.
But maybe the most important thing is prevention, great water quality so water changes! A diverse diet regarding ingredients that caters for what the fish feeds on in the wild.
I think discussing exposure to pathogens is another topic but….. there are definitely many pathogens that risks should be taken against.
References:
Bentzon‐Tilia, M., Sonnenschein, E. C., & Gram, L. (2016). Monitoring and managing microbes in aquaculture–Towards a sustainable industry. Microbial biotechnology, 9(5), 576-584.
de Bruijn, I., Liu, Y., Wiegertjes, G. F., & Raaijmakers, J. M. (2018). Exploring fish microbial communities to mitigate emerging diseases in aquaculture. FEMS Microbiology Ecology, 94(1), fix161.
Chu, W., Zhou, S., Zhu, W., & Zhuang, X. (2014). Quorum quenching bacteria Bacillus sp. QSI-1 protect zebrafish (Danio rerio) from Aeromonas hydrophila infection. Scientific reports, 4(1), 5446.
Cohen, F. S. (2016). How viruses invade cells. Biophysical journal, 110(5), 1028-1032.
D’Alvise, P. W., Lillebø, S., Wergeland, H. I., Gram, L., & Bergh, Ø. (2013). Protection of cod larvae from vibriosis by Phaeobacter spp.: a comparison of strains and introduction times. Aquaculture, 384, 82-86.
Dash, S., Das, S. K., Samal, J., & Thatoi, H. N. (2018). Epidermal mucus, a major determinant in fish health: a review. Iranian journal of veterinary research, 19(2), 72.
Diwan, A. D., Harke, S. N., & Panche, A. N. (2023). Host-microbiome interaction in fish and shellfish: An overview. Fish and Shellfish Immunology Reports, 100091.
Ksepka, S. P., & Bullard, S. A. (2021). Morphology, phylogenetics and pathology of “red sore disease”(coinfection by Epistylis cf. wuhanensis and Aeromonas hydrophila) on sportfishes from reservoirs in the South‐Eastern United States. Journal of Fish Diseases, 44(5), 541-551
Mokhtar, D. M., Zaccone, G., Alesci, A., Kuciel, M., Hussein, M. T., & Sayed, R. K. (2023). Main components of fish immunity: An overview of the fish immune system. Fishes, 8(2), 93.
Valladao, G. M. R., Levy-Pereira, N., Viadanna, P. H. D. O., Gallani, S. U., Farias, T. H. V., & Pilarski, F. (2015). Haematology and histopathology of Nile tilapia parasitised by Epistylis sp., an emerging pathogen in South America. Bulletin of the European Association of Fish Pathologists, 35(1), 14-20.
Van Valen, L. (1973). A New Evolutionary Law. Evolutionary Theory, 1(1):1-30.
Wang, Z., Zhou, T., Guo, Q., & Gu, Z. (2017). Description of a new freshwater ciliate Epistylis wuhanensis n. sp.(Ciliophora, Peritrichia) from China, with a focus on phylogenetic relationships within family Epistylididae. Journal of Eukaryotic Microbiology, 64(3), 394-406.
Wu, T., Li, Y., Zhang, T., Hou, J., Mu, C., Warren, A., & Lu, B. (2021). Morphology and molecular phylogeny of three Epistylis species found in freshwater habitats in China, including the description of E. foissneri n. sp.(Ciliophora, Peritrichia). European Journal of Protistology, 78, 125767.
Previously Tetradontiformes in South America were previously recognised as Sphoeroides and Colomesus but with the latest scientific evidence Colomesus has been synonymised with Sphoeroides. Sphoeroides (syn. Colomesus) contains two freshwater species, S. ascellus and S. tocatinensis, particularly the former is a frequent import for the aquarium trade.
Figure 1: The species of the revised Sphoeroides as described in Araujo et al. (2023).
This study used molecular phylogenetics to identify a phylogeny of the genus Sphoeroides (Fig 2) discovering the paraphyletic nature of Colomesus. The gene COI from the mitochondrial genome was used, which does beg the question how the phylogeny would differ with more genes including contributions from the nucleus.
Figure 2: Phylogeny of the South American Tetraodontiformes according to Araujo et al. (2023).
While this has changed a lot it’s possible more revisions and adjustments will be made, science has some level of opinion so it’s going to be an interesting future.
Source:
Araujo, G. S., Kurtz, Y. R., Sazima, I., Carvalho, P. H., Floeter, S. R., Vilasboa, A., … & Carvalho-Filho, A. (2023). Evolutionary history, biogeography, and a new species of Sphoeroides (Tetraodontiformes: Tetraodontidae): how the major biogeographic barriers of the Atlantic Ocean shaped the evolution of a pufferfish genus. Zoological Journal of the Linnean Society, zlad055.
Now this is only an introduction to my favourite dietary niche, I think. When algae eating is mentioned most will think about Loricariids, a 1,040 species strong family of Siluriformes (catfishes) according to Catalog of Fishes as of 2023 but many many more are to be described and discovered. It might be the small Otocinclus or the reasonably sized Pterygoplichthys and Hypostomus, if in the aquarium hobby even just a short time a wider diversity of this family becomes obvious with almost everyone having kept the common bristlenose, Ancistrus aff. cirrhosus or one of the ‘L numbers’ as they are called regardless if they have a number or not.
Baryancistrus chrysolomus, an algivore from the Rio Xingu, Brazil.
It’s also pretty well known that there are other fishes who do not rasp, maybe in the same way and feed on algaes, the diversity of Rift Valley cichlids who are a model taxa for adaptive radiation (McGee et al., 2020) has many species that frequently feed on algaes (McKaye & Marsh, 2020). The extent of their specialisation is certainly interesting given they are more then capable of generalisation where possible as explained in the Liems paradox (Liem, 1980). There is definitely the Gastromyzontidae, these are the hillstream loaches and looking at their mouth parts they don’t rasp in the same way to Loricariids.
So if not Loricariids what am I talking about? And ignoring those other groups? When looking at the mouth of any Loricariid you can’t help but notice those big rasping plates, part of the reason these are the suckermouth fishes. But are there others?
Loricariids obviously dominate South America, yet elsewhere that clade is not found. Africa, a vast but underrated continent when looking beyond the Rift Valley, we need to look no further then the secretly well known but diverse family, Mochokididae. I cannot even just express how fascinating this family is for algae raspers.
Synodontis brichardi
Synodontis, the genus anyone with Rift Valley will be aware of. But there is a lot more to this genus, they are found further then the Rift Valley and across the vast nature of Synodontis. There is also a wide diversity of diets within this genus (Yongo et al., 2019). Synodontis brichardi, S. shoutedeni and S. victoriae (Elison et al., 2018) are well known algae raspers, sometimes based on that very specialised rasping morphology. There has been little studies to whether they are able to generalise but in my personal experience I have seen Synodontis brichardi at least be able and willing to feed on live earthworms over algae, Liems paradox maybe?
There is one other Mochokidae you might not have heard of regarding algae rasping, Chiloglanis although others I shall not have the time to mention (Gerrinckx & Kegal, 2014) . A good sized genus, Chiloglanis (Van Wassenbergh et al., 2009) these feed on algaes and other Periplankton. They are not common in the trade but maybe they should be? As riverine fishes adapted to low flow maybe they should be?
Looking towards Asia Sisoridae (Mousavi-Sabet et al., 2021) could contain many algae raspers but maybe just adapted to that high velocity water?
The answer might be partially is there other taxa that might rasp on the algae or how much do we know about fish diets? Most understanding seems reasonably limited.
While I say all of this it doesn’t mean they are eating exclusively algae but maybe other periplankton or aufwuch by a specific feeding motion. The jaws outside of Loricariid seem to be a lot less diverse and more specialised competing I assume with other species and genera whereas Loricariidae dominate so much.
References:
Elison, M. V., Mlaponi, E., Musiba, M. J., NGUPULA, G. W., Kashindye, B. B., & Kayanda, R. J. (2018). Changes in the Diet of Synodontis victoriae and Synodontis afrofischeri in Lake Victoria, Tanzanian waters. African Journal of Tropical Hydrobiology and Fisheries, 16(1), 10-15.
Geerinckx, T., & De Kegel, B. (2014). Functional and evolutionary anatomy of the African suckermouth catfishes (Siluriformes: Mochokidae): convergent evolution in Afrotropical and Neotropical faunas. Journal of Anatomy, 225(2), 197-208.
Liem, K. F. (1980). Adaptive significance of intraspecific and interspecific differences in thefeeding repertoires of cichlid fishes. American Zoologist20,295 – 314.
McGee, M. D., Borstein, S. R., Meier, J. I., Marques, D. A., Mwaiko, S., Taabu, A., Kiche, M. A., O’Meara, B., Bruggmann, R., Excoffier, L. & Seehausen, O. (2020). The ecological and genomic basis of explosive adaptive radiation. Nature, 586(7827), 75-79.
McKaye, K. R., & Marsh, A. (1983). Food switching by two specialized algae-scraping cichlid fishes in Lake Malawi, Africa. Oecologia, 56, 245-248.
Mousavi-Sabet, H., Eagderi, S., Vatandoust, S. A. B. E. R., & Freyhof, J. Ö. R. G. (2021). Five new species of the sisorid catfish genus Glyptothorax from Iran (Teleostei: Sisoridae). Zootaxa, 5067(4), 451-484.
Van Wassenbergh, S., Lieben, T., Herrel, A., Huysentruyt, F., Geerinckx, T., Adriaens, D., & Aerts, P. (2009). Kinematics of benthic suction feeding in Callichthyidae and Mochokidae, with functional implications for the evolution of food scraping in catfishes. Journal of Experimental Biology, 212(1), 116-125.
Yongo, E., Iteba, J., & Agembe, S. (2019). Review of food and feeding habits of some Synodontis fishes in African freshwaters. OFOAJ, 10, 27-31.
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