VIII. Feeding Fish - Basic Health Factors and Care
This article discusses Herbivores, Carnivores & Omnivores
This article and the next will likely run a bit shorter than most posts. This is due to the relatively straightforward approach to feeding taken here at New England Aquaculture. It is the focus of feeding to nourish the health of your fish, providing optimum conditions for enhanced color and size often not seen in the wild due to predation and health factors. As such it is important to understand the different types of feeders in our aquarium. While many fish are omnivorous and will consume just about anything that is dropped in the tank, extra care needs to be taken with obligate feeders. Obligate feeders are either herbivores or strictly carnivores and within these two distinctions, their lays some overlap with omnivorous fish that have a strong preference one way or the other.
Herbivores
When we think of herbivores we may imagine a race between a tortoise and a hare to a bowl of salad and we are not wrong. Herbivores are animals that have evolved to consume plant-based material, they have complex digestive systems adapted to plant life and thus anything else consumed is poorly digested if at all. Consider our digestive systems, we have evolved to take nutrients from a vast number of sources, however, we never fully developed the skill tree for plant digestion, thus, apple peels and other roughage like corn husks pass through our system largely undigested. When we feed herbivores things they can not properly digest, it will simply pass through but not at the cost of energy. The more energy needed to process the food that can not be digested the more actual digestible matter the organism needs to survive.
In an aquarium, algae serve as the staple food source of herbivores. Rabbitfish and certain other tangs with specialized mouths like those in the "Bristletooth" family can be considered obligate herbivores; while they may accidentally consume some microcrustaceans in the process the clear focus of their intention is to consume algae. This makes them handy in keeping a tank clean, but, in doing this they inevitably will limit their own food supply. Beyond this, some algae have a composition that does not suit the palate of a given fish meaning you may see them eagerly cleaning one area and ignoring another area due to specific algae not being as preferred.
Because of this inherent fickleness for desired algae and the risk of malnutrition associated with depleted food sources, it is highly recommended that hobbyist who chooses to keep herbivores offer seaweed and macroalgae as part of a daily feeding regiment. This will assure a balance of nutrients are being introduced and that your fish is not consuming just the algae in your tank leading to health problems down the line. Seaweed(meaning sheets of Nori used in sushi) and macroalgae(meaning algae available to hobbyists like Chaeto and Gracilaria) can be added to the tank using a chip-clip affixed to a rock or other aquarium safe weight. If for some reason you do not have access to seaweed or macroalgae to put into your tank, you may soak leafy greens like lettuce in fish vitamin solutions and instead offer this in a pinch, but this should only be done until a source of seaweed or macroalgae can be found.
Carnivores
Some fish take a less vegetarian approach to hunger and will refuse any form of algae and seaweed offered. Eels, Lionfish, Sharks, and some Pufferfish can all be considered obligate carnivores. Many carnivores are capable of biting, nibbling, or otherwise breaking flesh to obtain their meal and more caution should be taken when feeding carnivores that may possess sharp teeth or beaks. Additionally, "meat" is quite loosely defined in some cases to include coral and invertebrates and it should in no way be assumed that a carnivore is a fish that only eats other fish. As with herbivores, consequently, a proper diet for some fish will need to be supplemented.
A large eel may begin attacking tank mates when hungry, sharks will search with increasing fervor sometimes breaching in an attempt to find suitable hunting grounds, or, your dogface puffer may start to rearrange your tank looking for food. All of these situations can result in a loss and to assure the happiness and health of all fish carnivores too should have special considerations made with diet. When feeding carnivores this means that you may need to introduce feeder fish for your predatory hunters to seek out and devour, or, that you may need to add some sort of sea flesh for them to nibble. Feeder fish are readily available at most fish stores but do not come without the risk of contracting diseases. It is suggested that a tank for feeder fish be established and maintained as you would a quarantine system to assure that you do not feed sickly fish to your predators. For carnivores requiring a more varied diet, you may be happy to make a trip to your local seafood counter to reduce the cost of prepared frozen foods available in pet stores.
Clam strips, scallops, shrimp and mussels all make great food sources for carnivorous fish. We purchase a few dollars worth of seafood, it is processed with vitamins and minerals and then we use small ice cube trays to freeze the seafood slurry into cubes. The cubes are thawed and drained and then the meat is fed to our carnivores. While there are loads of frozen foods available, true carnivores will not require many of the additives and supplements found in more omnivorously catered prepackaged foods designed for a wider more varied palette.
Omnivores
When observing fish and their feeding habits you will quickly notice that many “herbivores” also eat meat, and many “carnivores” will consume the stray algae or sponge in its path. This is because the vast majority of fish are not obligate feeders. The majority of saltwater fish consume a variety of food daily, from crustaceans and algae along the rocks to other fish and larger invertebrates. This diversity of diet ironically serves as a benefit to the reef enthusiast, when a fish is not specialized to a specific diet you may more readily change its diet.
Omnivores are not picky, they will happily try anything that floats by to see if it is food and thus, the majority of omnivores will easily convert to pellet or flake foods if frozen food will be too much hassle. One should use caution when feeding omnivores a diet strictly consisting of prepackaged dry foods. Many pellets and flake foods contain binders and stabilizers that are not readily digested, these ingredients like wheat germ and pea flour will quickly begin to rot once exposed to water or go undigested and be deposited as waste if consumed. Additionally, frozen food left unconsumed will go on to rot and cause nutrient imbalances in your tank so feeding should never be considered an all you can eat buffet to avoid excessive waste levels.
Whatever form of food is chosen, a strict water change routine is required to assure that the waste being added to your tank is properly removed, and, a varied offering should be given throughout the day. Fish eat constantly and the concept of feeding twice a day is only a bare minimum, instead consider feeding various food sources throughout the day, leaving no more food than can be consumed in a few minutes and repeating several times. This will assures that all tank inhabitants get a chance to eat and that excessive food is not left to rot need.