The Effect of Density and Photoperiod on Winter Flounder Survival, Growth, Behavior and Sex: Implications for Aquaculture and Stock Enhancement

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Elizabeth Fairchild UNH - Department of Biological Sciences Principal Investigator

I would like to be considered for NH Sea Grant Development Funds in order to complete the pilot study "The effect of density and photoperiod on winter flounder survival, growth, behavior, and sex: implications for aquaculture and stock enhancement." I am requesting $7,137 to do this, and have included a budget and budget justification. If you recall, I submitted a full proposal of a similar name for the RFP 2008-2009 funding initiative. Unfortunately, the 7 reviews ranged from excellent to fair, and the proposal was not funded by Sea Grant. Despite that disappointing outcome, it remains imperative that these critical uncertainties in standard winter flounder aquaculture practices are resolved in order to produce the healthiest fish both for grow-out and release.

To refresh your memory, the overall objective of this research proposal is to refine winter flounder rearing protocols to yield healthier fish. The basic techniques for culturing winter flounder have been developed but there are still issues relating to culture technology that need to be addressed. The first is a further investigation of juvenile stocking density. Occasionally, high incidences of fin erosion, in which fraying of the fin edges and erosion of the fin rays occurs. Although it is unknown if this condition affects the swimming or burying abilities of the fish, it is a possibility. Given this, and given that cultured fish released into the wild should not be disadvantaged because of morphology or behavioral differences, it is important to explore the issue of fin erosion. Winter flounder juveniles held at high densities, even for short periods of time, display elevated levels of cortisol, which suggests that stocking density can act as an environmental stressor. In addition, elevated rearing densities and increased agonistic behavior can affect sex determination in some species. One method which may reduce aggressive behavior, even at high stocking densities, is manipulating photoperiod. Studies with Japanese flounder have shown that fin nipping and other signs of aggressive behavior only occur during the day and not at night. In the past, I have reared winter flounder using 24L:0D photoperiod to promote growth, however, in hindsight, this may have been deleterious to the fish. A constant light photoperiod regime may have increased aggressive behavior resulting in stressed and fin damaged fish. Determining the effects of photoperiod and stocking density on growth, survival, aggressive behavior, fin condition, and sex are necessary in order to refine winter flounder rearing techniques.

Reviewers of the unsuccessfully funded proposal raised several concerns which I have taken into account to create a more competitive proposal. Three reviewers had concerns about comparing nutritional condition between wild and cultured fish using RNA:DNA ratios in the original plan. While I still believe that it is a valid index, I agree that this measurement needs more supporting evidence of its usefulness. Other reviewers had very helpful comments regarding experimental design (expandable tanks, density treatments, periodicity of aggressive behavior, isolation of treatments, statistical analyses) which I will implement in the future proposal.

I initiated a preliminary study at the UNH CML to address some of these rearing variables. A 2x3 randomized complete block experiment with 3 replicates was set up in which 57 dph flounder were stocked out into 2 photoperiod treatments (24L:0D, 12L:12D) and 3 density treatments (20,100, 300%). Density was measured as the ratio of total fish area to tank bottom area. A total of 1,614 fish were used such that 13, 64, and 192 fish were stocked into each of the 20,100, and 300% treatments, respectively. Each week, 10 randomly selected fish from each replicate were removed. Fish were anesthetized, measured, weighed, and photographed. A qualitative score of caudal fin erosion was assigned to each fish; scores ranged from 0 (complete fin erosion) to 5 (no fin erosion). Following data collection, fish were returned to their aquaria. The experiment ran for 10 weeks when the fish were >= 41 mm TL which corresponds to both the size when winter flounder can be sexed histologically and an appropriate release size for enhancement. At the end of the experiment after final measurements were taken, ten fish from each replicate (total n = 180) were saved in modified Davidson's fixative for histological analyses.

After 10 weeks, there was no effect of stocking density or photoperiod on growth of juvenile winter flounder. In addition, survival was not affected by stocking density. However, survival was on average 10 higher each week in the 12L:12D photoperiod treatments than in the 24L:0D treatments, suggesting that juvenile winter flounder exposed to a continuous light cycle may be more stressed than those under a more natural lighting regime. The effects of photoperiod and stocking density on the aggressive behavior and gonadal development of the juvenile flounder remain unknown. With Sea Grant development funds, the preserved fish can be processed histologically to determine sex, and these analyses can be completed.

This research addresses many Sea Grant strategic goals, particularly Sustainable Aquaculture Goal 1 (Develop and improve culture system technology for cold-water marine species), Goal 4 (Ensure that stock enhancement is economically and socially sustainable), and Goal 5 (Ensure that stock enhancement has minimal adverse impacts on the environment and wild stocks). In the hopeful event that completion of these preliminary experiments results in a fully funded Sea Grant project, commercial fishermen, UNH scientists, and the NMFS Milford, CT, laboratory will work together to complete this research thereby addressing Goal 1 of Conservation and Sustainable Utilization of Fisheries Resources (Develop new management strategies that utilize an ecosystem approach to stewardship of the fisheries resources). Because a portion of the funding will be used to support students, Marine and Aquatic Science Literacy, Part B: Developing a technically trained workforce Goal 2 (Encourage involvement of students) will apply.

There is a critical need to complete these studies in order to refine and improve protocols for winter flounder aquaculture and stock enhancement. These winter flounder samples have been preserved for over a year now, and there are no available funds to process them. With support from Sea Grant, this preliminary experiment can be completed and analyzed. Not only will the results prove useful in refining future experimental designs, but these preliminary data will be used as further justification for conducting larger-scale, more sophisticated experiments. These data combined with previous reviewers' advice will enable me to write a more competitive proposal for the next NHSG funding cycle which will lead to a stronger, larger, more refined study that fits the NH Sea Grant strategic plan.