Chapter 10: Feeds and Feeding
Dry formulated feeds are not generally given as a first feed for larval fish as the intestinal tracts have not developed enough to digest these complex feeds. As the fish get older and the intestine is more developed they should be offered dry formulated feeds. Formulated feeds have a number of advantages for use in the hatchery. First, they are easier to use than live feeds. Little effort is needed to prepare the feed compared to the effort and facilities needed to produce live feeds. Second, the feed quality is more consistent than live foods and no on-site enrichment is needed before the feed can be used. Formulated feeds are available in sizes as small as a rotifer, and in a variety of progressively larger sizes that make it easier to ensure the fast-growing larvae have an appropriate size food particle to consume. If the fish can be trained to accept formulated feeds in nursery ponds, the production can be increased over ten times what is possible where the fish are dependent on only in-pond production of natural food organisms resulting from pond fertilization.
Most larval fish feed on some type of zooplankton as a first food. However, as the larvae get older, the larvae of most fishes can be trained to accept formulated feeds. This training is referred to as the weaning period, the transition from one type of food to another or a smaller size food to a larger size food item. The new feed item is added initially at 25% or less of the total quantity of feed added/feeding, and each day thereafter the percentage of the new feed item is increased until only the new feed item is being given.
Larval fish are sight feeders and the swimming pattern of the live foods used in the hatchery help attract the attention of larval fish. Formulated feeds sink over time and do not show any of the erratic swimming patterns seen with live feeds that stimulates the fish larvae to strike at the food item. The larvae need to be fed small quantities of formulated feed frequently so they have a chance to strike at a food particle as it falls through the water column. Formulated feeds need to stay in the water column as long as possible to give the larval fish an opportunity to strike at the food particle. Feeds that sink slowly are preferred. The deeper the container where the larvae are held gives more opportunity for the larval fish to strike at the food particle as it drops through the water column, as most larval fish do not actively feed on formulated feed once it settles to the bottom of the tank.