The effect of dietary protein, lipid, and carbohydrate levels on the performance, metabolic rate and nitrogen retention in juvenile European lobster (Homarus gammarus, L.)

Abstract

Releasing hatchery-reared juveniles in the wild can mitigate the general decline in the natural stocks of European lobster, Homarus gammarus, L.. However, growth and survival rates in lobster culture are low, presumably due to suboptimal nutrition and feeding. With the aim of determining appropriate nutrient levels, we tested different formulated extruded feeds for the culture of juvenile European lobster. Baseline metabolism (standard metabolic rate, SMR), in combination with the metabolic cost of feeding (specific dynamic action, SDA), and nitrogen retention during digestion and assimilation was investigated for six experimental diets. Diets were formulated to contain two different levels of protein (400 and 500 g kg−1), with three lipid to carbohydrate (L:CHO) ratios (low, medium, and high). These experimental diets were tested over a 32-day period, against a conventional control diet (Antarctic krill, Euphausia superba). During this period, the growth performance of the juveniles was assessed as molting frequency, increments in carapace length and whole body wet weight. At the end of the growth performance trial, oxygen consumption (MO2) and nitrogen excretion rates of individual lobsters were determined prior to and following the ingestion of a single meal. Molting occurred more frequently in juveniles fed with krill and krill resulted in a significantly higher specific growth rate than experimental dry feeds except for the 500-low diet. However, lobsters fed any of the three 500 and the 400-low diets had carapace length increments, SMR, SDA, and nitrogen retention similar to those fed the krill diet. Results suggest that protein is an important macronutrient for juveniles of this species and must be included above 40%. Also, lobsters have a dietary requirement for carbohydrates ranging from 24% to 35% probably related to the need for glycogen in chitin synthesis. The lower the protein content, the higher the requirement in carbohydrates.