Brazilian Efforts Towards Minimization of the Use of Live Feed in Neotropical Fish Larviculture

Studies about the larviculture of the most aquacultured Neotropical fish have been carried at the Aquaculture Center since late 90´s. Basically, these studies are concentrated on two species considered as model of planktivore (pacu, Piaractus mesopotamicus) and piscivore larvae (surubim, Pseudoplatystoma spp). Both species depend on a constant supply of live food during the first days, and acceptance of formulated diet is low. However, the use of formulated diets in intensive larviculture is desirable in order to lower production costs and sustain large-scale production. Experiments were carried in order to establish technology to increase productivity during hatchery, by developing feeding techniques based on knowledge of the morpho-physiological characteristics of the larvae during ontogeny.

In both species, the olfactory organs develop precociously indicating that olfactory sense is of primary importance for food perception and capture. At first feeding, tasted buds (oral region) and free neuromasts (body surface) are present. Initially the digestion of surubim is based on alkaline enzymes, and the gastric glands appear when larvae is about 11 mm SL, coinciding with the increase of pepsin-like activity. In pacu, differentiated stomach is observed in larvae of about 10 mg. From this moment, pacu can be weaned with minimum growth delay, and the weaning success also depends on the diet quality. The diet utilization can be improved by supplementation with exogenous enzyme, and ingestion can be stimulated by the use of attractants (glycine, lysine and betaine). The contribution of hyperplasia to the skeletal muscle growth is higher in fast- than in slow-growing larvae. Hypertrophic growth is less affected by the undernourishment of pacu larvae. It is clear at this moment that the adequate food source during the first feeding of the pacu is critical for muscle growth in later phases. Surubim can be weaned to formulated feed after two weeks on live prey; however, in this phase high mortality and increased cannibalistic behavior are observed. The use of trash-fish larvae as prey is ineffective due to low survival, high cannibalistic rates and high cost per juvenile. The traditional method of feeding training for surubim (using mixtures of beef and formulated diet) is an economically viable strategy. Nevertheless, the inexpensive Artemia frozen biomass should be considered as an alternative method.

The information gathered in our research broadens the understanding of the initial development of Neotropical fish larvae, and allows for the improvement of feeding techniques while decreasing the use of live feeds.