Principal Investigator: David Bengtson and David Alves

Industry Partner: Marine Biotech, Inc.

Table of Contents

• Background/Observations
• Conditions/Techniques
• Results
• Conclusions

This project was proposed while co-PI David Alves worked at URI, but the proposal was not approved for funding until he had moved to Marine Biotech, Inc. (MBI), who then became industrial partners in the project. The official start date for this project at URI was Jan. 9, 2000, after all the proper paperwork had been filed.

MBI personnel, especially Tom Lauttenbach, began designing the system that would be used for exposing the fish to different current velocities during early 2000. A prototype was built and PI’s Bengtson and Alves visited the MBI facility in April to measure current velocities and discuss plans for construction of the final experimental system. During the week of May 8, MBI delivered the complete system to URI and Mr. Lauttenbach spent one week at URI assembling the system, except for hooking up the chiller. The latter task was accomplished by a private contractor hired by URI and this unfortunately took several weeks to complete.

Seawater was placed in the system and more weeks were required for the biofilter to develop sufficient capability to handle the anticipated ammonia loads. Finally, in early August, 2000, GreatBay Aquafarms (GBA) delivered a shipment of fish averaging about 250 g each to the URI facility. After a few weeks to allow the fish to acclimate to the facility and begin to feed properly, the first experiment of the project was started in early September.

The experimental design consisted of three treatments (water velocities) with three replicates each. Water velocities tested were a) < 5 cm/sec (Low), b) approx. 20 cm/sec (Medium), and c) approx. 40 cm/sec (High). The experimental tanks were shallow oval fiberglass tanks with one screened-off section in which the fish were held. A paddlewheel generated current of the appropriate velocity in each of the Medium and High tanks and a directed jet of inflowing water provided minimal current in the Low tanks. The experiment ran for 60 days, ending in early November. At that time, it was decided that the water temperature in Narragansett Bay would be too cold for any meaningful results to be obtained in a subsequent 45-day net pen trial. (Mini-net pens have been constructed and are available at URI for use next summer.)

Results of the experiment (see attached figures ) showed that the High velocity treatment was not conducive to fish survival. Although fish survival in the Low and Medium treatments was 100%, it was only 34% in the High treatment. Statistical analysis of growth (i.e., change in length or weight) showed no significant differences in growth in length (apparently the survivors in the High treatment were the largest fish in each tank). Nevertheless, the fish in the High treatment grew significantly less in weight than did the fish in the Low or Medium treatments, which were not significantly different from each other. Fish in the Medium treatment consumed significantly more feed than did those in the Low treatment, which in turn consumed significantly more than did those in the High treatment. However, no significant difference was apparent in food conversion ratio (FCR) between the Low (1.54 + 0.37) and Medium (1.37 + 0.23) treatments (we did not analyze FCR in the High treatment because of the low survival there).

This experiment, although incomplete because of the lack of net-pen follow-up, was instructive in a couple of ways. First, it allowed us to test the experimental system and obtain some preliminary results. Second, those results indicate that our High velocity treatments probably provide excessive current velocities for these fish. Because the 250- g fish are the largest that we will use in this set of experiments (subsequent fish will average approx. 40 and 120 g), we plan to reduce the current velocities to be tested in the future. We expect to obtain 40-g fish from GBA in January, 2001, and conduct a 60-d trial with them (no net-pen follow-up was ever proposed for them, since they would be too small for transfer to net pens). We then expect to receive 120-g fish from GBA in April and conduct a 60-d growth trial in the experimental system (late spring) followed by a 45-d growth trial in the net pens (early summer). Finally, we expect to receive another group of fish, approx. 200 g from GBA in July for another 60-d experimental plus 45-d net pen trial before the Narragansett Bay water temperatures cool in the fall of 2001.