The production of soft shelled blue crabs, (Callinectes sapidus Rathbun) using heated effluent with special considerations given to the effects of eyestalk ablation on survival and growth

From 17 September 1980 to 22 July 1981 blue crabs, Callinectes sapidus Rathbun were cultured to determine the feasibility of soft shell crab production at the Cedar Bayou Generating Station, Baytown, Texas. They were held in a pond in individual round cages from 17 September through 31 December, 1980; from 8 January through 30 April, 1981; and from 12 April through 21 July, 1981. The best season for crab shedding as determined by regression analysis of both weight and carapace width vs intermole period was between 17 September and 31 December. There was no significant difference in growth between crabs fed 20% of their body weight of fresh or frozen fish every other day and those fed 10% body weight every day. Survival was 100%. Percent growth was similar for green blue crabs held in compartments of either 18 x 25 x 30 or 45 x 45 x 30 cm. Survival was 100%. Crabs held in compartments at the surface grew better than those confined near the pond bottom. Crabs that had molted at an acclimation temperature of 20 C were put into each of five test temperature (20, 24, 26, 28 and 30 C) in 0.18 m3 plexiglass aquaria. Each aquarium was separated into eight individual compartments. Crabs held at 26 C had the shortest intermolt period. Molting rates increased as temperature increased from 20 to 26 C, but decreased from 28 to 30 C. Eyestalks of blue crabs averaging 13.1 +/- 0.6 cm in carapace width were ablated 15, 30 and 45 days after molting for the three groups and a fourth group remained unablated. Ablation at 15 days shortened the total intermolt period the most, but crabs ablated at 30 and 45 days molted within 2 to 7 days after ablation whereas crabs ablated at 15 days took an average carapace width of 14.1 +/- 0.5 cm molted no faster than those in the non- ablated group. Temperature and photoperiod also varied between the two experiments. Partial budget analysis indicated that stocking 1,800 rather than 900 crabs to a 0.1 ha pond and feeding every other day rather than daily would increase returns and that the use of ablation to shorten the time crabs were held would greatly increase returns.