There is a lot of information about fish nutrition, but a lot of misinformation and constantly regurgitated myths as well. Some of the ideas center around the need for variety, the quality of prepared foods, how misleading some of the labels can be, and much more.
The goal for any aquarist should be to provide a complete and balanced diet. How they get there is where the debate starts. There are many different methods of trying to reach this goal, and most are flawed in one way or another.
Variety of prepared foods:
Some aquarists try to achieve a complete and balanced diet by feeding a variety of prepared foods. This is not necessarily the worst approach, but is unlikely to give the best diet possible. At the most basic level foods are not all equal, so why feed one good food, one okay food, another okay food, etc. This is just diluting the nutrition in the best food in the mix. The idea is that any shortcomings in one food will be countered by another food. The truth is that this is unlikely. If one food is lacking something that another food is providing that other food is probably a better source of the other nutrients as well.
'Natural'... isn't:
Some people prefer a natural diet and try to feed many foods that are in a more natural form, but this is also flawed. These foods are far from natural in almost every case. No fish naturally eats lettuce, carrots, cucumber, zucchini, etc. So the fact that these are in their natural form does not make them any more natural for a fish to eat than a pellet. Even the aquatic based foods are not part of the natural diet for fish. Fish do not naturally eat brine shrimp, scallops, prawns, fish fillets, etc. These are also just as unnatural for a fish to eat as pellets. Even more importantly is that these foods will not provide a complete and balanced diet. In most cases the aquarist is feeding a variety of frozen foods (brine shrimp, bloodworms, etc.) and these are all mainly a protein source. Although there are other nutrients in these foods besides protein, they are minimal, incomplete, and unbalanced. These foods are equivalent to the first few ingredients in a high quality pellet, which are there for protein. These diets lack all of the other ingredients that are in a high quality pellet that provide all the other nutrients vital to their diet.
Live Foods:
Live foods are one way many people try to simulate a natural diet, which again can be quite flawed. Most live foods are far from natural. The most common live foods are food for very few fish in nature, and not foods to the fish we feed them to. Goldfish, guppies, and rosey reds are not part of the natural diet of oscars, jack dempseys, bichirs, arowanas, etc. In addition, live food fish are horribly cared for. They are overcrowded (which is guaranteed to spread disease), poorly cared for (inadequate water changes), and underfed with poor diets (so they are in poor condition when purchased at the pet shop). This leaves very little nutrition to pass on to the fish that eat them, and are almost guaranteed to unnecessarily introduce pathogens sooner rather than later. They are also far from nutritionally complete or balanced. Many aquarists have found a difference in the aggression level in fish never fed live foods and those that are fed live foods. This means there is a higher risk of aggression problems with fish fed live foods. Some aquarists raise their own live foods, either specifically for feeding or they feed the culls of fish they are breeding. This fixes the problem of the horrible condition of store bought feeder fish, but not the other issues. Too decrease the chances of introducing pathogens many aquarists raise and keep non-fish foods. These would be things like black worms, white worms, earthworms, insect larvae, etc. This does decrease the chances of introducing pathogens since they are not fish, but there is still some risk. In addition these foods are still far from complete and balanced nutrition, sometimes very high in protein. These foods can be a great way to get fish into breeding condition and even trigger breeding, but are not a good staple of a diet to be fed all the time due to the imbalance of nutrition.
Homemade foods:
This is another way aquarists may try to go above and beyond to provide the best food possible, but may not. Although there are some specific diets that work very well for certain aquarists, these are more the exception than the rule (and usually only work for one or a few species). The best ones include a variety of protein foods (either frozen or fresh), some fruits and vegetables, vitamin and mineral supplements, and frequently a gelatin to help the food keep its form. The ingredients are blended and then either frozen or put in the refrigerator. The biggest problem with this method is that the aquarist is trying to be a fish nutritionist, which ends up being guesswork at best. Unless the aquarist is also a trained animal nutritionist they are simply guessing and hoping. Nutrition is the most under-appreciated aspect of fish care (and the care of any animal and humans) and leaving it to an amateur's guesswork is not in the best interest of the fish.
Specific ideas that are not correct:
There are some exceptions to some specific commonly accepted ideas as well.
Invertebrates can have foods with copper in them. Although copper can be toxic to them, and there may be foods out there that have a toxic form or level of copper in them, the fact that any particular food has a copper ingredient in it doesn't mean it can't be fed to shrimp, crayfish, etc. In fact, copper is a vital component of their diet and without it they can develop health problems long term. Although this need is minimal, as part of trace elements in the diet, it is still an important part of their diet.
Another misconception is that certain types of fish require certain foods in their diets. For example, many aquarists think that algae eaters need algae in their diet (or a wafer shaped food with algae in its name). This is not true. Although they have adapted to eat algae in nature, this is their way of achieving a complete and balanced diet, but not the only way they can get proper nutrition. As long as the ingredients are easy enough to digest they can get a complete and balanced diet from a high quality pellet. In addition, most wafer shaped foods with algae in the name are much more similar to any pellet food than most people realize. In most cases most companies vary the formula very little from one food to the next. They change the color of the package and the dyes used to color the food, and little else. They may add a little (or a little more) spirulina to an algae or veggie formula, but the actual nutrition is almost identical (or exactly identical) to every one of their other foods. This is because people expect this and that is what they are selling to, people (not fish). This is not just the case with algae and veggie themed foods, but in most cases all of the foods made by a particular manufacturer vary little nutritionally from one formula to the next.
Goldfish requiring a different food than tropical fish is another big misconception. This gets into a whole article's worth of myths about goldfish, but to summarize they are not coldwater fish, they are eurythermal. This means they can do well in a very wide range of temperatures, including tropical. Not only have they been introduced and naturalized into almost every aquatic system that almost all aquarium fish come from, their natural range includes some of the most tropical areas on the planet. They are herbivorous omnivores meaning they eat both plant and animal based foods, but mostly plant based. They can do well on many diets and have no special needs compared to any other aquarium fish.
Misleading labels:
The packaging and claims used by some companies can be very misleading to the average aquarist. As explained above being a veggie or algae formula doesn't mean the food is significantly different from other foods. Most companies use artificial colors to give the foods a colorful appearance pleasing to the human, but not beneficial to the fish in any way. This can be used to make the food seem more appropriate for a particular type of fish (such as dying veggie and algae formulas green, foods for carnivorous fish red or orange, etc.). They may also mix two different colored pellets in the same package to make it seem like more of a variety when really the green and brown pellets could have the exact same nutritional value. Companies are also more than happy to use buzz words like spirulina, garlic, etc. These foods may have very little of these ingredients in them, or they may be in forms that are ineffective. In some cases the trace amount of spirulina may be the only difference between the veggie food and the company's foods for carnivorous fish.
Another issue is the ingredients themselves. Some companies use meals that are made up of the scraps left over after a particular animal is processed for human food. Other companies will use the entire animals in their meals, making them much more nutritious. This way companies using scraps can make them sound very nutritious by listing 'shrimp meal', 'salmon meal', etc. as their first ingredients, when really it is only bones, scales, heads, and organs. Another tactic is to use ingredient splitting. For example the third and fourth ingredients may be 'wheat meal' and 'wheat flour', when really together wheat makes up a larger portion of the food than the bone and head scraps listed as the first two ingredients. Preservatives are another issue that companies can be misleading about. When listing a preservative it may only be what is already in the meals, as required by law. With other companies it may be that the preservative is added directly to the food as a whole.
Special ingredients like garlic can be misleading. Whether the aquarist has heard that garlic is good for fish, or it is a holdover from human food, listing garlic on the label can help sell food (even if it is a low quality form with an insignificant amount in the food). Garlic in particular is debated. Some aquarists think it is nothing more than an appetite enhancer, others think of it like an essential in any diet. Garlic can be a powerful appetite enhancer, invaluable when an aquarist is trying to get newly acquired fish to eat (especially wild caught specimens). Scientific studies have shown that garlic actively kills some parasites, and can even be used against some bacteria, fungi, and parasites. This is supported by the experiences of some aquarists who have successfully used it to treat certain illnesses (such as white spot disease in a reef aquarium where medications cannot be safely used).
Frequency of feeding:
Feeding frequency may not be debated very often, but is probably not thought about enough. Most aquarists probably feed once or twice a day, perhaps skipping a day once a week, regardless of the type of fish being fed. Although the fish have been domesticated and may have adapted to such a diet, this may not be ideal for most species. Most aquarium fish are adapted to feeding on small amounts of food very frequently, effectively feeding constantly in some cases. They naturally forage for food all day long and eat food in small amounts at a time, spread out through the day. In aquariums they are forced to eat as much as possible once or twice a day. This is okay, but if an aquarist can feed more frequently it is more natural for the fish. This is the case with almost all community fish, herbivores of all types, and juveniles of all fish. Even big carnivores like Oscars should be fed small amounts frequently when young. As they grow the frequency should be decreased and the amount per feeding increased, until they are feeding only once or twice a week as adults. In most cases it is not needed, but using an automated feeder that can feed four to six times a day would be an effective way to mimic this natural feeding behavior. The only exception to this would be in tanks with fish with different feeding responses. For example, if there are fish that will feed very aggressively and others who will be much more timid when it comes to feeding, feeding small amounts frequently will allow the aggressive feeders to eat all the food every feeding, leaving the less aggressive fish to starve. In these cases it is better to feed one or two larger meals each day. In addition, feeding pellets that are too large to be swallowed whole by the aggressive feeders is a good way to keep them occupied since they will each grab a pellet and hold on to it as it softens in the water, giving the less aggressive fish an opportunity to feed. A smaller pellet could be fed to the less aggressive feeders once the aggressive feeders are occupied.
Some basics about preserving the nutrients that are there:
There are some important things for any aquarist to know about nutrition. These apply to fish food as well as food for other pets and for humans. There are five main factors that remove or destroy nutrients in food: heat, light, water, oxygen, and time. Minimizing the effects of these factors will keep fish food as nutritious as possible for as long as possible.
To protect food from heat simply keep it at room temperature or cooler. For long term storage it can be kept in the refrigerator or freezer. It can be very cost effective to buy food in bulk, store most of it in the freezer, and only use a small container to store small amounts for immediate use near the aquarium. Do not keep food on top of the light fixture. This is a source of heat and keeping the food on it all of the time is a good way to gently bake away some of the nutrients.
Light can also destroy some of the nutrients in fish food. This is one reason why most containers of food are completely opaque or have only a small window to view the food. Pellets are better protected because only the nutrients on the surface of each pellet are exposed to light, the rest of the food being well protected. Some brands may use packaging that allows for more visibility of the food with pellets. Flakes are particularly vulnerable to light since every bit of the food is exposed to light. Most packaging will keep the food well protected from light.
Water can remove nutrition, particularly water soluble vitamins. This is why presoaking foods before feeding them to the fish is not a good idea. Again flakes are particularly vulnerable, but in most situations when pellets are soaked they are soaked completely through under the impression that if this is not done the pellet may dangerously expand in the fish's stomach. This is not true. Pellets do not expand significantly in water, and if they did the fish could simply regurgitate some of the food. Water vapor in the air can also remove some of the nutrition. This is one reason why a tightly sealing container to store the food in is so important.
Oxygen also degrades some of the nutrition. This is the main reason why a tightly sealing container to store the food in is so important. This is also why the same is true of human foods and why some foods are packaged with pure nitrogen instead of just air. Do not leave fish food containers open and the food should be well protected from oxygen. If there is any doubt about how well a container seals (such as some of the resealable pouched foods) using a tightly sealing container made for human food could be a good alternative.
The final factor is time itself. Discard any food that is discovered at a later time (such as when cleaning out the aquarium's stand). Buy food with the latest expiration date. This should be the product behind the others on the shelf if the store is rotating their stock properly when new product is put out (which is in their best interest so it won't expire and become a loss for them) but is not always the case since the average employee does not care and has no real interest. This is especially true of products that hang on a peg instead of simply being placed on the shelf because they require more effort to rotate. Buy food in quantities that will be used in a reasonable amount of time, ideally less than a year. When buying in bulk most of it should be stored in the freezer to keep it fresher longer, and again should be used within a year.
The best form of food:
High quality prepared foods can provide all the nutrition fish need. By including high quality protein sources and all the necessary supplements (all the other things in that long list of ingredients) they provide all the nutrition that fish need. Most importantly they do this in every bite. If the food is mixed the fish can pick through it for more desirable foods. Any animal has a natural drive for certain nutrients because in nature certain things are hard to come by and when they are available the animal should take as much as it can. This can be fat, sugar, salt, etc. When they are available the animal needs to get as much of it as possible to get a complete diet overall. This is why humans are driven to fat and sugary foods. In nature these are hard to come by (and were in our history). But today they are too easy to come by. That doesn't make the urge to eat as much of them as possible when they are available go away, it just makes us keep eating them. This is the same for fish. Just because they have a high drive for certain foods doesn't mean that food is necessary or a healthy part of a complete and balanced diet. Having all the nutrition in every bite (such as in a flake or pellet) is the best way to ensure that all the nutrition makes it into the fish. The ideal form for a fish food in most cases is a pellet. The nutrients are better protected, the fish make less mess with pellets versus flakes which preserves water quality, and they fill the fish up better. Even small fish like small schooling tetras and dwarf species of rasboras can eat pellets. Many high quality foods come in a very wide range of pellet sizes, so there is something for almost every type of fish out there, even fry.
Variety is not a nutrient:
This may tie in with some of the methods many aquarists use to try and achieve the real goal of a complete and balanced diet for their fish, but is significant and needs more discussion. Variety is not a nutrient. It is not a protein, carbohydrate, lipid, mineral, or trace element. Variety is one method that most aquarists use to try to achieve the real goal of a complete and balanced diet, but it is not a requirement. Even if an aquarist is stuck on the idea of variety being essential, high quality prepared foods are effectively a wide variety of foods,in the proper proportions, to create an even better diet than a physical variety of foods could achieve.
How can a food be judged:
The reason there is so much debate about what really is the best diet for fish is because there are more than enough foods out there today that are good enough to not cause problems short term. This means that an aquarist can take almost any food off the shelf, feed it to their fish, and have good enough results. People are complacent and without a lot of reason to do so they will not change what is working well enough for them. So unless they were to feed a food that causes immediate negative effects they will likely stick with what they are using. If their fish are lucky some knowledgeable fish store employee or a fellow aquarist will talk to them about a specific food and get them to improve the quality of the diet they feed their fish.
But the real issue is that there are a lot of good foods out there now and it can be very hard to differentiate between them based on quality. Very little scientific research is done that can even be applied to this hobby, especially something as direct as food trials with different brands. So that is not something that will help differentiate between foods. Aquarists' experiences are extremely valuable, but can also be extremely flawed. If an aquarist is asked why they feed a certain food the answer is almost always something to the effect of 'my fish are doing well on it so I see no need to change it', and may also include 'they are doing better than they did on other foods I have tried'. This really means that their current food is not as bad as others they tried and their fish are doing well enough.
What it comes down to now is medium term success versus long term success. There are too many factors involved with how well fish will do long term that even a long list of success stories cannot be considered alone as proof of the quality of a given food. Most current foods will provide medium term success, but long term success is the next level and still hard to reach. Most fish die because of something the aquarist did wrong, whether the water quality was constantly worse than it should have been but not bad enough to cause immediate problems, or there were subtle problems with the nutrition that were not visibly observable. Almost no fish die of old age in an aquarium. In effectively every case they die of long term subtle problems with their care. An aquarist judges the health of his fish visually, but this overlooks all the internal problems that can develop over time that are not visibly obvious. One common issue is fatty deposits. Most foods contain too much fat for an adult fish to stay healthy on. The excess fat can end up as fatty deposits throughout the body and eventually lead to death. Foods with over 10% fat are fine for young, growing fish. But this level of fat can lead to fatty deposits if fed to adult fish as a staple.
There are four main factors that are commonly used to measure success with particular foods: growth, health, color, and breeding. These are the four main factors that can be measured, qualitatively or quantitatively, by any aquarist.
Growth may be the most common factor used, but can be extremely flawed. The reason for this is that it takes little more than a lot of protein to achieve rapid growth. This is one method commercial fish farms can get fish to a sellable size in only months, they also have no need to focus on long term success since the fish they are caring for are only for food. So although a lack of growth could be something to be concerned about, focusing only on growth rate can result in severe oversights with the rest of the nutrition.
Health is a major factor in determining the quality of a food. Obviously bad foods don't introduce pathogens and cause disease, but lower quality foods can cause more health problems long term than higher quality foods. High quality food will provide all the nutrients the entire body of the fish needs, so the immune system will be in the best condition possible and all organs will be functioning to their full potential. This leaves only the minimal chance of stress to the fish, and stress is what allows for illness. So by providing the best nutrition possible, the aquarist will minimize all possible internal stressors to the fish and therefore have an overall reduced frequency of any health problems. Obviously other factors can greatly affect the health of fish, but proper nutrition can decrease the frequency of health problems.
Coloration can also be a strong factor in determining the quality of fish food, but can also be affected by some other factors. The highest quality foods will provide proper nutrition that allows fish to reach their maximum potential, including coloration. However, there are ways to alter coloration and produce unnaturally colorful fish with food. Some foods contain hormones that increase coloration, giving the appearance of proper nutrition without actually providing it. Some foods contain so many strong dyes that the fish are artificially colored by the high concentration of artificial colors in the food. This can even create false coloration (such as whites being an orange or yellow tint). This is one reason to avoid foods that contain any artificial colors. Outside of these factors it takes a very poor diet and/or significant stress for fish to demonstrate poor coloration, so an aquarist claiming the food they use produces great colors in their fish actually means very little. There are some examples of foods being so high in quality that the colors were observably improved. These usually involve cichlids and other species to whom color is much more significant (demonstrating social status, maturity, allowing for mate selection, etc.). Bringing these fish into impressive coloration is a notable achievement for a food. But this still requires this improvement to be above and beyond the usual coloration these fish generally display. The best examples are when the food is changed and subtle colors become more obvious. This can be a new sheen to the whole fish, or localized increased pigmentation (such as on the gill cover). These may sound subtle, but if one food can allow the fish to display these colors and another cannot, it demonstrates the higher quality of the food that is allowing the fish to do this.
Breeding success is another factor that can be used to determine the quality of a food. In order for most fish to breed they have to be in the best condition possible. In order for an organism to invest massive amounts of energy and nutrients into breeding one of two scenarios have to be in place, either 1-they are in such good condition they can spare the energy and nutrients or 2-they are severely stressed and the breeding is a last ditch effort because in all likelihood they will die soon and this is their last chance at reproduction. The second scenario is not the common way to trigger breeding in aquarium fish, so that leaves the first scenario. This means that not only are the fish getting everything they need to grow well and maintain a healthy condition, they have so much excess that they can afford to dump a significant amount of energy and nutrients into reproduction. Therefore successful reproduction is a good indicator of a high quality diet, and more specifically increased success in reproduction (in frequency and yield per occurrence). Obviously many species reproduce quite easily, some are hard to prevent breeding. So successful breeding in species like convict cichlids, the common livebearers, mbuna African cichlids, etc. is not necessarily indicative of a high quality food. A significant increase in the success of that reproduction could be. For example, if African cichlids or swordtails are breeding and the food is changed and now more of them are breeding and the broods are larger, that is indicative of a higher quality food. Another way breeding can indicate a higher quality food is that the females are in better condition after the breeding. Because of the energy and nutrient costs of breeding many females can be in a relatively poor condition after breeding, even requiring separation. If one food allows females to be in a better, healthier condition than another food, that food is higher in quality.
One final factor allowing for the quality of the food to be determined, and arguably the most important, is success in unique species. This means that a particular food produces success in species that no other food has yet to achieve. This can be getting fish that usually only eat live foods to accept prepared foods, or getting hard to keep species to simply stay alive and healthy. This is what few foods have achieved. There are many species of fish out there that are not good candidates for captivity because they are so difficult to keep alive that effectively all of them are doomed to die in captivity, usually of starvation. Prepared foods that are truly the best are allowing some of these species to have success in captivity that had not been achieved previously. This is what can truly prove a particular food or company is above and beyond all the others currently available, and that it is arguably the best food on the market (for now).
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