The growth energetics of postlarval lobsters (Homarus americanus)
fed a brine shrimp diet (Artemia salina; 51% protein, protein:carbohydrate
= 5.1) were compared with the energetics of lobsters fed
three artificial diets. The artificial diets were pelletized shrimp
meal diets, varying in both protein (16.65-23.30%) and carbohydrate
content (22.85-31.27%) and the protein:carbohydrate ratio (0.5-1.0).
The best growth was measured among lobsters fed the brine shrimp diet
and the 23.30% protein diet, followed by the two lower protein diets.
The protein efficiency ratios (g wet wt. gain/ g dry wt. protein fed)
were inversely related to the protein level of each diet.
All diets were assimilated at the same level (~ 9 0% ) but there
were significant differences in food consumption rates, respiration
rates and ammonia excretion rates among lobsters from the four experimental
groups. Although all lobsters were given equal rations in
grams, the artificial diets were lower in caloric content than the
brine shrimp and the pellets were fragmented by the lobsters during
the feeding process, resulting in significantly lower (P <0.01) food
consumption rates of the artificial diets.
Respiration rates measured immediately after feeding were significantly
lower among lobsters fed the three artificial diets than
those fed the brine shrimp diet; the increased respiration rate of
the latter group of lobsters reflects an increased calorigenic effect due to the higher protein level of the brine shrimp diet. Ammonia
excretion rates of lobsters from the four groups were significantly
different from one another ( P <0 . 01) and were directly correlated
with the protein level of each diet. The O:N ratios (atomic ratio
of oxygen consumed to NH+ -N excreted) measured in the four experimental
groups were inversely related to the protein level of the
four diets, indicating an increased dependence on carbohydrate catabolism
for energy production with low dietary protein levels. The
reduced growth rates of lobsters fed the two lower protein diets were
apparently a result of differences in the amounts of food consumed
and not increased energy expenditures or reduced assimilation
efficiencies.Prepared for the Department of Commerce, NOAA
Office of Sea Grant under Grant #04-7-158- 44104
