OOA Progress Report for the period 1/01/01 through 12/31/01
Principal Investigator: David A. Bengtson and David Alves
Accomplishments
Scheduled Tasks:
The objectives of this project are a) to determine the water velocity conditions that maximize growth of summer flounder juveniles during the nursery phase, from approximately 40 g to 200 g body weight, and b) to test the performance in small, experimental net pens of summer flounder that have been raised at different water velocities prior to transfer to the net pens. Lab trials are conducted in shallow raceway tanks at high, medium and low velocities (3 replicates of each) and field trials are conducted in cages strung from a dock, with replicate-to-replicate fidelity from lab to field. Because of the longer-than-expected start-up time for our facility during the first year of the grant (calendar year 2000), we needed to move some tasks to the second year (calendar year 2001). During the first year, we had completed only one 60-d lab trial with fish that were approx. 257 g at the start of the experiment. That trial ended too late in the fall to put the surviving fish out to cages in Narragansett Bay for the field portion of the trial. Our re-scheduled tasks for year 2 were: a) conduct a 60-d lab trial with 40-g fish (no field trial as the fish would be too small), b) conduct a 60-d lab trial and a 45-d field trial with 120-g fish, and c) conduct a 60-d lab trial and a 45-d field trial with 200-g fish.
Progress on Tasks
In year 2, we attempted to conduct the 60-d lab trial with 40-g fish, but suffered disease problems with subsequent high mortality and terminated the trial after about one month. A complete cleaning and bleaching of the system, along with restarting the biofilter, set us back in our schedule. Nevertheless, by early July, we were able to begin a 60-d lab trial with 124-g fish. In early September, those fish were placed in cages adjacent to the dock at URI's Narragansett Bay Campus for a 45-d field trial. In early October, a group of larger-than-expected fish (387 g) were placed in a lab trial for 30 d, then moved to an intended 30-d field trial. Monitoring of the cages after one week indicated almost complete mortality in the field trial, likely due to rough conditions from an offshore storm. The 387-g fish were the last group available to us following the quasi-demise of GreatBay Aquafarms, so no further experiments were possible.
Important Results or Findings
Our most important finding is that summer flounder reared in tanks grow best at "medium" velocity, i.e., 15-20 cm/sec, roughly equivalent to a one-quarter to one-third knot current. Fish fed better in that treatment, probably because the current kept the food pellets suspended longer in our system. In the one field trial that we were able to conduct, there was no difference in cage survival for fish that had been reared at "low" vs. "medium" velocities in the lab. Specific results are as follows (and here we include results with 257-g fish from year 1 to provide the full story): Three experiments, two of 60-d duration and one of 30-d, were conducted with different water velocities in tanks, using fish of 124 + 4 g (exposed to 0, 15, or 30 cm/sec for 60 d), 257 + 12 g (exposed to 0, 20, or 40 cm/sec for 60 d) and 387 + 13 g (exposed to 0, 15, or 30 cm/sec for 30 d), in a raceway system with adjustable paddlewheels. For all of the size groups of fish, survival was significantly reduced at the highest current velocity. For the 124-g fish, survival in the high velocity treatment (26 + 1 %) was significantly lower than that in medium velocity (57 + 7 %) and in low velocity (67 + 6 %). For the 257-g fish, survival in high velocity (35 + 19 %) was significantly lower than that in medium and low velocities (100% in both cases). For the 387-g fish, survival in the high velocity (50 + 11 %) was significantly lower than that in medium velocity (98 + 2 %); all 387-g fish in the low velocity treatment were lost due to a system malfunction. For both 124-g and 257-g fish, growth in the medium velocity treatment was significantly better than that in the low velocity treatment, which in turn was better than that in the high velocity treatment. For 124-g fish, growth was 76 + 12 g, 49 + 8 g, and 39 + 0 g in the medium, low and high velocities, respectively. For 257-g fish, growth was 47 + 10 g, 25 + 4 g, and -7 + 17 g (weight loss) in the medium, low and high velocities, respectively. For 387-g fish, growth at medium velocity (26 + 6 g) was significantly greater than that at high velocity (-22 + 8 g). Food consumption data from the 257-g fish showed that the fish in medium velocity grew most because they consumed significantly more food during the experiment (1622 + 128 g per tank) than did fish in low velocity (915 + 65 g), which in turn consumed significantly more than fish in high velocity (640 + 90 g). Nevertheless, there was no significant difference in food conversion ratio (FCR) between fish at low velocity (1.54 + 0.37) and those at medium velocity (1.37 + 0.23). At the end of the experiment with 124-g fish, fish from the low-velocity and medium-velocity treatments were moved to cages in Narragansett Bay, where currents of about 1 knot (approx. 55 cm/sec) are routine. After three weeks in the cages, no significant differences in survival were observed (low velocity = 83 + 12 %; medium velocity = 81 + 2 %). Subsequent damage to some of the cages and escapement of the fish precluded further statistical analysis of survival, as well as any growth measurements. We conclude that current velocities of 15-20 cm/sec in the nursery improve growth of juvenile summer flounder, that current velocities of 30-40 cm/sec are excessive, but that increased current velocity in the nursery does not improve fish survival upon transfer to cages.
Difficulties Encountered
- Failed laboratory trial with 40-g fish: As mentioned above, we suffered high mortality in the laboratory trial with 40-g fish. Samples of those fish were delivered to Drs. Marta Gomez-Chiarri and Roxanna Smolowitz, who have an NRAC project to study diseases in summer flounder. We are still awaiting their final results. The disease event caused us to have to completely clean and re-start our system, biofilter, etc.
- While not necessarily a problem, the fact that summer flounder did not survive well in the lab trials in high-velocity treatments meant that we only compared survival of low-velocity and medium-velocity fish in the field cages.
- In the field trial that we conducted with 124-g fish, some of the cages developed holes and fish escaped. We present survival data only for the first month of the trial, because after that one treatment had escapees from two of the three replicates. Similarly, we did not collect growth data at the end of the field trial, because a) the fish were significantly different in size when they entered the cages, and b) data from only one replicate could not be subjected to statistical analysis.
- In the lab trial with 387-g fish, we lost nearly all fish in the low-velocity treatment due to a malfunction of our system. Again, those fish were delivered to Dr. Gomez-Chiarri for examination and we await her results. Because we had already established that medium velocity yielded better growth and because the lab trial with those fish only began in early October, we hoped that 30 d at the different velocities would provide sufficient lab growth data and also be sufficient to "condition" the fish for a field trial before water temperatures dropped too low. After 30 d, we had lost the low-velocity treatment and had only 50% survival in the high-velocity treatment. Nevertheless, after putting liners on the cages to prevent any more escapes, we put the three replicates from the medium- and high-velocity into their corresponding replicate cages. As mentioned above, almost all these fish died within the first week of the cage trial, so we have neither survival nor growth data for this field trial.
Our original proposal called for more experiments on fine-tuning of the lab current velocity studies in year 2. For example, given that medium velocity of 15-20 cm/sec provided significantly better growth in all cases, we would like to test velocities of 10, 15 and 20 cm/sec to specifically identify the optimal current velocity. Unfortunately, GreatBay Aquafarms is no longer able to provide us with fish of appropriate size to conduct these experiments.
Reports, Manuscripts, and Presentations Resulting from the Project
An undergraduate student who was working on this project as part of the Coastal Fellows program at URI presented a poster on the work with 124-g and 387-g fish at the Coastal Fellows poster celebration in December, 2001. Presentations on the full project will be made in the flatfish session at the Aquaculture America meeting in San Diego in January, 2002, and at the Milford Aquaculture Seminar in New Haven in February, 2002. A manuscript is being written for submission to a publication that will emanate from the flatfish sessions in San Diego and Beijing (WAS meeting in April, 2002).
Tasks and activities for next reporting period
Tasks for the next reporting period
Make the aforementioned presentations and write the manuscript for the flatfish sessions volume.
Work plan to accomplish tasks
Prepare slides for the presentations.
Concerns or difficulties
None anticipated
Expenditures
Expenditures were in the range anticipated, except that we transferred money from operating to personnel (with UNH approval) when it became apparent that GreatBay would not be able to supply the last group of fish.