The zebrafish diet is age-dependent. Starting on day 5-7, larvae must be fed because by that time their yolk has been depleted. In the days thereafter, the fish grow extremely rapidly, making quantity and quality of the feed during this phase of the utmost importance. The larvae are not yet able to handle large food particles (prey) and the food offered must be sized to meet this limitation. For live food, Paramecia (150-200 μm protozoans) and Rotifera (250 μm wheel animals), are ideal.
Once the larvae are big enough, they can also be fed the slightly larger brine shrimp (Artemia nauplii). After one month, larvae can be given flake or pellet food as well. Adult zebrafish are always provided live food, in addition to flake or pellet food; live food is a type of enrichment; they can hunt for it.
Amount of food
There are two ways to ascertain whether zebrafish have enough to eat at each feeding: feeding to satiation and body weight-related feeding. With the first method, the fish do not receive more food than what they can consume in a certain time span, e.g. 5 or 10 minutes. Although relatively simple, this method has the disadvantage that the amount of food ingested is not really known, and that it is subjective. The other method provides a body weight-related quantity, e.g. 50-300% for fast-growing larvae and juveniles, and 1-10% for adult fish. This means that the weight of the fish must be estimated based on its size, which requires experience, and can be a challenge. Changes in body weight and other parameters, such as length, could be determined at the time the fish have to be manipulated for other reasons.
In zebrafish husbandry, the amount of feed depends on the purpose for which the animals are kept: since reproduction requires a lot of energy, breeding fish are given more food.
Fish that are held on maintenance, i.e. when they are not used for breeding, are given less. The feeding rate for a maintenance population of adult zebrafish might be 3% of body weight in feed per day, as opposed to 5% for growing fish and fish held for egg production.
Because zebrafish do not have a proper stomach and are relatively small, a frequent feeding regimen of small meals seems to work best. In practice, the animals are fed twice a day on weekdays and once a day during weekends. Larvae grow fast, so they must be fed on a regular basis with ample food. In practice, larvae are fed 2 to 3 times per day.
The feeding regimen has an effect on the water quality: food that has not been ingested – because it is provided in excess or incorrectly – will stay in the system and pollute the water. Flake food, if used, contains particles of various sizes. Particles that exceed the fish’s bite size, are often left over. Consequently, it is better to provide a mix of uniformly sized feed, such as suspensions, or pellets that match the bite size of zebrafish.