Primary Questions of Nutritional Physiology That Would Combine the Whole Life Cycle In Culture of South American Pseudoplatystoma Destined for Conservation and Industrial Purposes

The genus Pseudoplatystoma contains 8 species of catfishes and they belong to largest migratory species in South America. These species have been decimated in the wild due to overfishing and environmental changes affecting their reproduction. They attract commercial interests, both for industrial culture and ornamental trade. We summarize the current understanding of the nutrition related physiology of these species, identify shortcomings and suggest further research. Examination of the olfactory system in early ontogeny suggests that larvae are nocturnal and are guided by their sensory system in feeding. We have concluded that larval catfish grown solely on Artemia naupli outperform fish offered formulated diets and live Tubifex, although cannibalism was lower in fish fed purified dipeptide based diets. To evaluate the protein and lipid requirement of Pseudoplatystoma, nine semi-purified casein-gelatin-lecithin based diets containing three levels of protein (40-50%) and three levels of lipid (12-20%) were tested. Juvenile fish were fed at a restricted-readjusted feeding rate for 8 weeks. The diets resulted in an average body weight increase of 21.2 ± 2.9 fold. The feed conversion ratio was affected by the dietary lipid level. At the 40% protein level, increasing the level of dietary lipid had a positive effect on final weight (protein sparing effects). Whole body protein and moisture contents were affected by the dietary level of lipid.  Ash content was not affected by the dietary protein/lipid levels whereas several mineral levels, Na, K, B, Mn were affected. Whole body lipid content positively correlated with the level of dietary lipid. Fatty acid composition of the whole body was affected by the dietary lipid level in the case of both neutral and phospholipids. Polyunsaturated fatty acids increased with increasing levels of dietary lipid while saturated fatty acids decreased. Our preliminary results suggest that surubim can utilize a high level of dietary lipid, and the optimum protein/lipid ratio might be close to 45/16%. We also used a stable isotope labeled amino acid (15N) to examine differences in the protein turnover ratio among groups fed diets with distinct levels of proteins/lipids. Studies on effect of broodstock feeding were inconclusive as a protein level in the range of 28 to 40% did not appear to affect gonad maturation. No viability of eggs was examined as a result of the variability in the composition of the diets. We ultimately discuss the implications of these findings for further expansion of the management programs, aquaculture and aquarium trade.