Almost all species of fish can be trained to eat a variety of prepared diets, but not all diets are equally acceptable to all fish. Even the most nutritious diet cannot maintain a fish that fails to recognize the type of food. Recognition is affected by instinct, and by training. The interaction of feeding stimuli is complex. Security, hunger and the state of health are important motives that are easily overlooked. Water quality, temperature, & illumination are especially important. Cycles that include reproductive, tidal, solar and reproduction-control feeding activity in the wild & may persist in tank-reared fish.
When a new fish is introduced into an aquarium, it may or may not eat right away. If the tank is rearranged to mimic a natural environment, the fish may be calmed and may feed better. Providing a well landscaped aquarium for fish is never a mistake! Occasionally the tank may be so brightly lit that fish will refuse to eat. The intensity of illumination should be reduced if fish are hiding or in clusters in a corner.
Fish locate food by various chemical, visual, or chemical clues. After a fish has located a potential meal, they may taste and examine it before they swallow it. Many predatory fishes consume prey quickly and later regurgitate food that may be unsuitable. Because of the many differences of fish species, generalisations about the most important sensory characteristics would be inappropriate. Fish CAN be trained to accept new foods which may not involve previously important clues.
Flavors: Taste is very important for most species, but especially significant for bottom feeders and other fish in turbid water. There are specific anatomical receptors for taste and smell, but flavors must be dissolved in water to be detected. Although some food ingredients stimulate fish to feed, fish do not respond to the same chemical stimulants as humans. For example, seafood is an especially strong attractant and sweets or fats are less effective.
Sound: Some fish, such as channel catfish, respond to the scattering of food throughout a pond. Some will congregate in the feeding area even before the fish farmer arrives to feed, possibly because they have detected his footsteps or other routine sounds.
Buoyancy & color: Fish which have adapted to feeding at the surface may not pursue food which has settled at the bottom. This is due to the buoyancy of the food in which they are used to eating. Also, some bottom dwellers may not surface to eat floating food, but the majority of aquarium fish are less picky. Shallow water fish have good color vision, and color may be an important feeding stimulus.
Feeding of predatory fish: Many fish which are predacious are not easily trained to eat nonliving foods. Predators will use scent or touch to locate food or are triggered to feed by visual stimuli. Some species feed from peculiar characteristics of certain live foods that are important in trigger feeding. These detection’s involve vibrations, visuals and even changes in electrical fields. To train newly introduced predators that are currently eating only live foods, continue to offer their preferred foods until the fish is eating regularly, then reduce the amount offered. Substitute freshly killed food on alternate days. You may have to simulate movement, such as dropping the food into water currents at the tank surface, to attract the attention of fish. You can introduce soft meaty foods for a portion of the killed food in later feedings. If prepared food is still refused, you can coat the dry food with the smell of their preferred live food. This training is easily attained by younger individuals before they have developed their inflexible habits of eating live foods.