results in overcrowding and stunting and minimizes the 

 possibility of reproduction outside of the hatchery and the 

 likelihood of unwanted introductions. After sex-reversal, fry are 

 gradually acclimated to seawater over a period of 1 week, then 

 transferred to nursery tanks for a period of rapid growth prior to 

 stocking in sea cages. 



Construction of a new pilot-scale hatchery to support 

 experimental research as well as extension projects in the Caribbean 

 was completed in April 1987 on Lee Stocking Island. The design and 

 operation of the hatchery, consisting of six 34-m^ broodfish tanks, 

 twelve 6.5-1 egg incubators, sixteen 560-1 rearing tanks for sex 

 reversal of fry, and eight 4.9-m^ tanks for seawater acclimation of 

 sex-reversed fry, were described in detail by Ernst (in press). The 

 hatchery incorporates a system for recirculation of water through 

 biofilters, a critical design feature in the Bahamas where limited 

 groundwater resources must be conserved. Multiple recirculation 

 systems permit simultaneous testing of separate salinity regimes for 

 broodstock holding and sex-reversal so that optimal salinities for 

 maintaining broodstock and rates for acclimation of fry to seawater 

 may be determined experimentally. Spawning, incubation of eggs and 

 sex-reversal of fry may be conducted at any salinity up to that of 

 full seawater (36-37 ppt ) . 



During the period April 9 to July 27, 1987, a total of 796,613 

 and 536,668 eggs and fry were collected from hatchery broodfish 

 units maintained under salinities of 3-6 ppt and 18 ppt, 

 respectively (Ernst, unpublished data). 



DEVELOPMENT OF METHODS FOR ADAPTATION OF FLORIDA RED TILAPIA TO 

 SEAWATER 



Gradual acclimation of fry to seawater following sex reversal 

 (approximately 35 days post-hatching) has been found to generally 

 result in good survival and growth in seawater. However, the 

 requirement for low-salinity water for maintaining broodstock and 

 for early rearing increases infrastructure costs for recirculation 

 of water and restricts the siting of future hatcheries to areas 

 where low-salinity water is available. Considerable research 

 emphasis at CMRC has been placed on the development of seawater 

 acclimation methods that minimize the requirement for low-salinity 

 water during the hatchery phase of production and that maximize 

 survival and growth in seawater. 



Selection of optimal life stage for seawater transfer 



Low-salinity water requirements during the hatchery phase of 

 production may be reduced by acclimating stocks to seawater at early 

 stages of development. Early acclimation may be accomplished by 

 initiating seawater transfer during the early fry stages or by 

 incubating and hatching eggs at elevated salinities (Watanabe, Kuo 

 and Huang, 1985a, b). This approach may be limited by the fact that, 



340 



