Jay Hemdal
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Fish Medic
Fish Nutrition – Short Bites
Proper nutrition of captive fish is a very complicated subject. Virtually everything known about this topic is derived from fisheries science and therefore is related to growing fish for human food – where the fastest growth rate is most important. Long-term captive fish in aquariums have different needs. The following are some snippets of information regarding diets and feeding of aquarium fish, with the emphasis on giving information about the main issues, with the least amount of text.
Proper nutrition is vital to all animals. The fish in your aquarium rely solely on you to meet all of their dietary requirements, and their food must be provided in sufficient quantity to supply the energy they need in order to grow. The diet must also have the proper balance of fats, proteins, and carbohydrates, as well as the proper amount of vitamins and minerals.
On the other hand, too much food or food that is too high in calories will cause the fish to become obese. Not all fish have the same dietary requirements, and their needs even change as they grow. To top it off, over-feeding an aquarium can result in deteriorating water quality that will harm the fish.
Mixing medications with focus + food: This cannot work unless you calculate the dose properly. General Cure should not be dosed orally, as the two components have two different oral doses. This article discusses that: https://www.reef2reef.com/ams/proper-dosing-of-medicated-foods.780/
Using dietary supplements as a “medication”: The best diet in the world will not stop active infections – this is called the “chicken soup” syndrome. A proper diet is of course important for long-term fish health, it's just that changing to "great diet" will not stop any active fish diseases. Think of your pet dog – feeding it a great diet will do nothing to stop a flea or tick infestation if you take it for a walk in an infested field!
Adding vitamins or food additives to the aquarium’s water: Don’t do that. This just feeds the heterotrophic bacteria. Aquatic animals, if they uptake vitamins from the water at all, do so slower than the bacteria does.
True vitamin deficiencies: These are rare in fish. The two most common deficiencies are with Vitamin E and Thiamin (B1). These often need to be supplemented as they are not in great enough levels in many seafood items.
Food amounts: Some reef aquarists tend to underfeed their fish in order to try and limit nutrient and waste levels that would cause algae issues. This is not humane for the fish. Better to limit the number of fish in the reef tank instead. Some other aquarists may overfeed their fish. The one thing that they can do for their fish is to feed them, and some people take that to the extreme.
Fish not eating: Acute anorexia (where a fish suddenly stops feeding, or never starts feeding, and soon dies) is usually caused by some environmental issue; water quality problems, disease, transport stress or tankmate aggression. Chronic anorexia is a rarer problem, where the fish has apparently adapted well to captivity in all respects except that it does not show a normal feeding response. This can be due to the species’ natural history (only feeding on coral for example) or can sometimes be caused by collection with cyanide. Be sure to evaluate a non-feeding fish right away and take steps to resolve any environmental problems. Don’t fall into the trap of assuming the fish will begin feeding when it gets hungry enough, or conclude it must be eating something, just not when you are watching. A fish that does not actively pursue and consume food that you offer it is going to have problems surviving for the long term.
Fatty liver disease (Hepatic lipidosis): A major chronic health problem facing most long-term captive fishes is “fatty liver disease,” or liver degeneration. Fish do not assimilate fats well, so often, if a fish's diet is too high in fat, it will then be deposited in various tissues, especially the liver. Unlike with mammals, this fat is not readily usable during times of starvation. Even if food is withheld from a fat-laden fish, very little of the fat is ever reconverted into usable energy. Some fish do not show outward signs of obesity, especially sedentary species such as groupers and lionfish. In these, fatty liver disease may only be diagnosed after death, when sections of the liver will show oil droplets and pieces of the liver itself will float in seawater. With many animals, a period of acute anorexia can cause liver damage.
Fatty liver disease is most common in adult fish whose growth rate has slowed considerably. Younger fish tend to grow fast enough to minimize fat deposition—excess calories are turned into muscle tissue instead. With long-term captive fish, fatty liver disease is the leading cause of (or contributor to) death. Virtually every lionfish held in captivity longer than three years will show evidence of fatty liver disease upon necropsy.
Thiaminase: This is an enzyme that metabolizes or breaks down thiamine (vitamin B1). In high enough concentrations in food, thiaminase will create thiamin deficient diets in fish. This is a common, yet serious problem with predatory fish that are fed feeder goldfish, as goldfish are very high in thiaminase. Lionfish, piranha and oscars cichlids were commonly fed all-goldfish diets by home aquarists. Health issues in their fish were then very common; fatty liver disease in lionfish, pica in piranha (where they eat each other to try to get more thiamin). Fresh seafoods known to be high in thiaminase can be supplemented with thiamin. Conversely, aquarists can avoid feeding fresh seafoods known to be high in thiaminase.
The actual impact of thiaminase on a fish’s diet depends on three factors:
What proportion of thiaminase-containing food is fed to the fish
What the concentration of thiaminase is in the food item
How much vitamin B1 is already present in the food
Frozen foods: Food in the pet supply chain is not always handled very well. For decades, there have been issues with frozen fish foods being repeatedly thawed and refrozen while going from the manufacturing plant to your home. Each cycle degrades the product. It is really bad with brine shrimp...in that case, the subsequent refreezing causes large ice crystals that pierce the shrimp's body, allowing virtually all the nutrients to leak out.
Proper nutrition of captive fish is a very complicated subject. Virtually everything known about this topic is derived from fisheries science and therefore is related to growing fish for human food – where the fastest growth rate is most important. Long-term captive fish in aquariums have different needs. The following are some snippets of information regarding diets and feeding of aquarium fish, with the emphasis on giving information about the main issues, with the least amount of text.
Proper nutrition is vital to all animals. The fish in your aquarium rely solely on you to meet all of their dietary requirements, and their food must be provided in sufficient quantity to supply the energy they need in order to grow. The diet must also have the proper balance of fats, proteins, and carbohydrates, as well as the proper amount of vitamins and minerals.
On the other hand, too much food or food that is too high in calories will cause the fish to become obese. Not all fish have the same dietary requirements, and their needs even change as they grow. To top it off, over-feeding an aquarium can result in deteriorating water quality that will harm the fish.
Mixing medications with focus + food: This cannot work unless you calculate the dose properly. General Cure should not be dosed orally, as the two components have two different oral doses. This article discusses that: https://www.reef2reef.com/ams/proper-dosing-of-medicated-foods.780/
Using dietary supplements as a “medication”: The best diet in the world will not stop active infections – this is called the “chicken soup” syndrome. A proper diet is of course important for long-term fish health, it's just that changing to "great diet" will not stop any active fish diseases. Think of your pet dog – feeding it a great diet will do nothing to stop a flea or tick infestation if you take it for a walk in an infested field!
Adding vitamins or food additives to the aquarium’s water: Don’t do that. This just feeds the heterotrophic bacteria. Aquatic animals, if they uptake vitamins from the water at all, do so slower than the bacteria does.
True vitamin deficiencies: These are rare in fish. The two most common deficiencies are with Vitamin E and Thiamin (B1). These often need to be supplemented as they are not in great enough levels in many seafood items.
Food amounts: Some reef aquarists tend to underfeed their fish in order to try and limit nutrient and waste levels that would cause algae issues. This is not humane for the fish. Better to limit the number of fish in the reef tank instead. Some other aquarists may overfeed their fish. The one thing that they can do for their fish is to feed them, and some people take that to the extreme.
Fish not eating: Acute anorexia (where a fish suddenly stops feeding, or never starts feeding, and soon dies) is usually caused by some environmental issue; water quality problems, disease, transport stress or tankmate aggression. Chronic anorexia is a rarer problem, where the fish has apparently adapted well to captivity in all respects except that it does not show a normal feeding response. This can be due to the species’ natural history (only feeding on coral for example) or can sometimes be caused by collection with cyanide. Be sure to evaluate a non-feeding fish right away and take steps to resolve any environmental problems. Don’t fall into the trap of assuming the fish will begin feeding when it gets hungry enough, or conclude it must be eating something, just not when you are watching. A fish that does not actively pursue and consume food that you offer it is going to have problems surviving for the long term.
Fatty liver disease (Hepatic lipidosis): A major chronic health problem facing most long-term captive fishes is “fatty liver disease,” or liver degeneration. Fish do not assimilate fats well, so often, if a fish's diet is too high in fat, it will then be deposited in various tissues, especially the liver. Unlike with mammals, this fat is not readily usable during times of starvation. Even if food is withheld from a fat-laden fish, very little of the fat is ever reconverted into usable energy. Some fish do not show outward signs of obesity, especially sedentary species such as groupers and lionfish. In these, fatty liver disease may only be diagnosed after death, when sections of the liver will show oil droplets and pieces of the liver itself will float in seawater. With many animals, a period of acute anorexia can cause liver damage.
Fatty liver disease is most common in adult fish whose growth rate has slowed considerably. Younger fish tend to grow fast enough to minimize fat deposition—excess calories are turned into muscle tissue instead. With long-term captive fish, fatty liver disease is the leading cause of (or contributor to) death. Virtually every lionfish held in captivity longer than three years will show evidence of fatty liver disease upon necropsy.
Thiaminase: This is an enzyme that metabolizes or breaks down thiamine (vitamin B1). In high enough concentrations in food, thiaminase will create thiamin deficient diets in fish. This is a common, yet serious problem with predatory fish that are fed feeder goldfish, as goldfish are very high in thiaminase. Lionfish, piranha and oscars cichlids were commonly fed all-goldfish diets by home aquarists. Health issues in their fish were then very common; fatty liver disease in lionfish, pica in piranha (where they eat each other to try to get more thiamin). Fresh seafoods known to be high in thiaminase can be supplemented with thiamin. Conversely, aquarists can avoid feeding fresh seafoods known to be high in thiaminase.
The actual impact of thiaminase on a fish’s diet depends on three factors:
What proportion of thiaminase-containing food is fed to the fish
What the concentration of thiaminase is in the food item
How much vitamin B1 is already present in the food
Frozen foods: Food in the pet supply chain is not always handled very well. For decades, there have been issues with frozen fish foods being repeatedly thawed and refrozen while going from the manufacturing plant to your home. Each cycle degrades the product. It is really bad with brine shrimp...in that case, the subsequent refreezing causes large ice crystals that pierce the shrimp's body, allowing virtually all the nutrients to leak out.
