GROWTH AND SURVIVAL OF SHRIMP CULTURED IN WATER WITH DIFFERING IONIC PROFILES

Susan Laramore* and John Scarpa
 Harbor Branch Oceanographic Institute at Florida Atlantic University
 Aquaculture and Stock Enhancement Program
 5600 US 1 North
 Fort Pierce, FL 34946 USA
 slaramo1@fau.edu

Interest in low salinity shrimp culture has existed for a number of years due to the possibility of rearing shrimp inland. In the late 1990s, production of the Pacific white shrimp, Penaeus vannamei, was successfully accomplished at HBOI using fresh well water. Since that time, low-salinity culture of marine shrimp has been successfully accomplished in the Southeast U.S., Mexico and elsewhere. Groups in Florida and the Southeast U.S. have undertaken low-salinity culture of marine shrimp; however, unexplained low survivals still persist. It was soon realized that successful production of shrimp at low salinity was dependent on the ionic profile of source water and that all source water was not equal (i.e., different ionic composition). Previously reported research compared the short-term (5-7 d) survival of PL 12-20 P. vannamei exposed to various ionic profiles in an effort to determine minimum and maximum concentrations for Ca, Mg, and K and the effect of interactions of these ions at various concentrations. Concentrations and combinations that resulted in excellent short-term survival (>90%) were then evaluated for a longer term (i.e., 6 weeks).

Growth and survival was assessed bi-weekly and at experimental termination, respectively, of P. vannamei exposed to different ionic treatments (n=5 reps/trt) at salinities of 2 or 4.  Fifteen shrimp (0.3-0.75 g) were stocked per tank (60 L for 2, 4 ppt and 80 L for 4 ppt) in a clear water RAS system for each ionic treatment.   The treatments were: Instant Ocean (control), and 4 ionic  profiles (Ca:Mg:K, H=high, L=low for each ion; HLL, LHL, HHL, LLL).  Final weight was significantly (p=<0.0001) lower at 2 ppt for both the control (2.7 g) and HLL treatment (4.8 g) compared to the other three treatments (5.4-5.75 g). In both of the 4 ppt experiments, growth was significantly (p=0.0008, p<0.0001) lower for both the control (6 g, 5 g) and LHL (6 g, 4 g) treatment compared to the other three treatments (6.8-8 g, 6.4-6.6 g).  Survival at 2 ppt was lowest for the control (70%) and LHL treatment (68%) compared to the other treatments (90-100%).  Survival at 4 ppt was lowest for the HLL treatment (50%) compared to the other four treatments (68-95%) in the first experiment and for the HLL (68%) and HHL (72%) treatments compared to the other treatments (80-95%) in the second experiment.    

These results suggest that regardless of the ionic profile, overall growth is higher at 4 ppt compared to 2 ppt.  These results also suggest that waters with either high Ca or high Mg coupled with low concentrations of the other two ions (i.e., K and Mg or K and Ca, respectively) may result in lower growth or survival than waters containing high concentrations of both Ca and Mg or lower than recommended levels of all three major ions. As suggested previously, the ratios of Ca, Mg, and K are as important as merely making sure that minimum ionic concentrations are present.  Ratios and minima should be considered when evaluating the ionic composition of potential culture water.  (Supported by the FL Aquaculture Research Council.)