Larval Nutritional Physiology: Studies with Clarias gariepinus, Coregonus lavaretus and Scophthalmus maximus

Abstract

Studies on the nutritional physiology of larval fish should provide the basis for defining the length of the larval period and for understanding the quantitative and the qualitative feed requirements of the larvae. For these purposes, it is necessary to perform both descriptive investigations on the ontogenesis of structures and functions as well as experimental investigations on adaptive strategies of the larvae under changing feeding regimes. In the present communication, examples of both approaches are discussed comparing three species: African catfish Clarias gariepinus, whitefish Coregonus lavaretus, and turbot Scophthalmus maximus.At the onset of exogenous feeding, the digestive system of all three species is sufficiently developed to ensure efficient utilization of live food, but not of dry food. A major event during the subsequent development is the differentiation of the stomach. Evidence exists that for turbot and catfish, a functional stomach is necessary to utilize dry feeds as efficiently as live feeds. Therefore, from a nutritional point of view, in those two species the larval period, during which a special larval diet has to be given, ends with the completion of stomach differentiation.The capacity of the larvae to acclimate physiologically to different nutritional conditions seems to be limited. Using general nutritional indices such as protease activity, RNAIDNA ratio, midgut cell height or nuclear diameter of hepatocytes, larvae of the three species show partly starvation symptoms when reared on dry food. This effect can be explained to some extent by quantitative considerations, i.e., lower food consumption and digestibility is less for dry diets than for live diets. The contribution of the qualitative factors involved in the different performance of larvae reared on dry or live food is presently not well understood. Future studies shonld: 1) investigate why utilization of dry diets depends on presence of the stomach; 2) define more precisely the quantitative feed requirements of larvae; and 3) search those diet-induced qualitative differences of larval metabolism which affect growth performance. harengus)

Digestive Enzymes in Larvae and Juveniles of Farmed Sharpsnout Seabream (Diplodus puntazzo) (Cetti, 1777)

“…Enzymes related to metabolism (digestion, absorption and transport) of proteins, lipids and carbohydrates from the egg and yolk reserves have been detected following fertilization and immediately after hatching [55][56][57][58].…”

Histo-Architectural Changes in the Selected Tissues of Litopenaeus vannamei (Boone, 1931) Juveniles Reared in Inland Ground Saline Water (IGSW) fed with Graded Levels of Potassium (K+) and Magnesium (Mg2+) through Feed

“…Fontagne, et al, (1998) observed in common carp, that due to deficiency of dietary phospholipid, resulting an increase in height of mucosal epithelium, a reduced total liver volume, mean hepatocyte volume and an accumulation of fat droplets in the enterocytes of the anterior intestine. A reduction of the enterocyte height has been used as an indicator of starvation in larvae (Segner et al, 1993;McFadzen et al, 1994;Theilacker and Watanabe, 1989). Regarding the good growth of carp larvae fed Artemia or phosphatidylcholine-enriched diets (Geurden et al, 1998), result showed the decrease of enterocyte height was not due to underfeeding conditions, and it might be because of active lipid absorption with diffuse appearance.…”

Effect of Dietary Regimes on Development of Digestive System of Stinging Catfish, Heteropneustes fossilis (Bloch) Larvae

“…In C. gariepinus, it has been reported that although larvae were able to be reared on microdiets from the onset of exogenous feeding, their growth rates were not comparable to those fed live food until their stomach became functional (Verreth and van Tongeren 1989;Verreth et al, 1992). Therefore, the larval period in terms of nutrition ends with the completion of a functional stomach (Segner et al, 1993), and consequently, the stomach differentiation is considered as a decisive event in the nutritional physiology of larvae and could be used as an external marker for the start of weaning (Verreth et al, 1992;Senger et al, 1993).…”