Effects of Temperature and salinity on growth, food conversion, survival and temperature resistance of juvenile blue crabs, Callinectes sapidus Rathbun
Holland, J. Selmon, Jr.
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Caged juvenile blue crabs, Callinectes sapidus Rathbun, (5-40 mm) were maintained at different temperatures (15-35 C) and salinities (1-21%) for 30-45 days. Underwater weight was recorded for individual crabs at 5-day intervals. Growth, yield and food conversion efficiencies were calculated. Mortalities and molts were recorded daily for caged crabs. All crabs were fed a pelleted artificial diet. Uncaged juvenile blue crabs were maintained for 25 days at combinations of three temperatures (20, 25 and 30 C) and three substrates (glass, sand, and sand-plus-shell). Survival for uncaged crabs was recorded after 15 and 25 days. Weights of initial groups (N=50) of uncaged crabs and of survivors after 15 and 25 days were recorded. Survivors from the various experiments were subjected to lethal temperatures (36-42 C). Survival time, sex and weight were recorded for crabs in lethal temperature tests. Growth and food conversion were closely related to temperature. The optimum temperature was 29-30 C. Yield (weight gain) and survival were also temperature related but were affected differently for caged and uncaged crabs. Yield of caged juvenile blue crabs was indirectly related to mortality. Mortality was directly related to temperature above 30 C. Yield of uncaged blue crabs was directly related to mortality, which varied directly with temperature (20-30 C). The latter effect was due to cannibalism. Substrate affected cannibalism among uncaged juvenile blue crabs. A sand-plus-oyster shell combination provided better survival than either sand or glass substrate. There appeared to be no difference between sand and glass substrates in preventing cannibalism. Very low salinity (1%) was apparently lethal to small blue crabs at optimal growth temperatures (29-30 C). Salinities above 1% had no significant effect on growth, yield, food conversion or survival. The upper incipient lethal temperature of juvenile blue crabs appeared to be 33 C, based on a 45-day cage study, attributing all deaths in that study to temperature stress. One thousand minute TLm for crabs acclimated to 20, 25 and 30 C were 37.1, 38.6, and 39.4 C, respectively.