A long-term assessment of the physiological effects of herring (Clupea harengus) as a dietary component of the American lobster (Homarus americanus)

Given the economic and ecological importance of American lobster (Homarus americanus) to the western North Atlantic, particular attention has been on factors that may increase susceptibility to disease. However, little focus has been on the possible role of dietary stress. There is strong evidence that wild lobsters feed on bait in traps, typically herring (Clupea harengus), yet evade capture. If the bait is nutritionally insuffcient for lobsters, then the pervasive use of bait (up to 3 kg for each kg of lobster harvested) may compromise the health of lobsters, thus making them more susceptible to diseases. it has been shown previously that lobsters fed a diet solely of herring had higher incidences of shell disease and were less likely to survive than lobsters fed other diets. Here, physiological status including haemolymph protein, calcium, sodium, potassium and magnesium, hepatopancreas moisture and ash content, and the mineral constituents, thickness and hardness of the cuticle of lobsters fed 100% herring was compared to that of lobsters fed a diet consisting of rock crab (Cancer irroratus), blue mussel (Mytilus edulis) and Spirulina algae. An artificial diet, as well as paired combinations of the three diets were also included for comparison. Juvenile lobsters (approximately 1.25 years of age) were fed one of these six diets for c. 330 days. Diet most affected the cuticle minerals, and lobsters with increased incidence of shell disease had a lower ca/P ratio. Although few physiological parameters correlated to the previously observed disease and survival results, all physiological parameters tended to change with diet, and those lobsters fed herring overall increased haemolymph and cuticle mineral values and had lower shell physiological values than lobsters fed the other diets. These results suggest that rather than affecting lobsters via a single mechanism, nutritional stress is likely to impact a number of physiological variables, and thus make it diffcult to assess health status through a single parameter.