Progress 10/01/01 to 09/30/04
Outputs
This project was intended to investigate the use of lipid to spare protein in diets for a new aquaculture species, summer flounder, raised in a water current of 15 cm/sec, and to examine the potential for replacement of fish meal with plant protein in diets for the same species. Only one commercial hatchery was producing summer flounder during this period, and they only produced fish 1-2 times per year. Thus, we were occasionally hampered by lack of experimental fish (see below). In 2002, after a mass mortality of fish from the hatchery, we had to rely on wild-caught fish from a local estuary (which took months to adapt to tanks and pelleted feed) to examine diets that contained 50% protein:10% lipid and 40% protein:20% lipid, with fish in a 15 cm/sec water current, as well as the 40:20 diet with fish in no current. In 2003 we used the remainder of the wild-caught fish to perform a counterpart experiment to examine both 45% protein:15% lipid and 35% protein:25% lipid
diets in 15 cm/sec current conditions. In both the 2002 and 2003 experiments, there was a great deal of within-replicate variability in growth (fish were individually marked so that growth measurements were made on each fish). Thus, no significant differences in growth were seen between the treatments. Proximate analysis of fillets and carcass showed no significant differences in percentages of protein, lipid, or ash among the treatments, nor were there any differences in moisture content. Similarly, there were no significant differences in carcass weight, fillet weight, liver weight, fillet yield, hepatosomatic index, or viscerosomatic index among the treatments. Because of the growth variability, fish in each tank were divided into sub-populations (those above vs. below mean growth increment for the tank) for further regression analysis of growth vs. all of the variables mentioned above. The results yielded many significant relationships, although few generalizations can be made
based on protein:lipid composition of the diets. The only striking result of this analysis was that fish in the no-current treatment exhibited no significant regressions. In early 2004, a large batch of juvenile summer flounder was obtained from the hatchery so that three experiments could be conducted on the replacement of fish meal with plant proteins. Unfortunately, these fish developed flounder infectious necrotizing enteritis, a disease caused by Vibrio harveyi, so they could not be used and the hatchery did not produce any more summer flounder until after the project period ended. Those plant protein experiments will be conducted in 2005.
Impacts
Fish feed manufacturers may want to increase the lipid levels in diets for summer flounder, depending on their willingness to accept our experimental results including a large amount of growth variability among individual fish for each of the diets we tested.
Publications
- No publications reported this period
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Progress 01/01/03 to 12/31/03
Outputs
In 2003 we conducted the counterpart experiment to the one completed in 2002, which examined diets that contained 50% protein:10% lipid and 40% protein:20% lipid, with fish in a 15 cm/sec water current, as well as the 40:20 diet with fish in no current. In 2003, we examined both 45% protein:15% lipid and 35% protein:25% lipid diets in 15 cm/sec current conditions. As in the 2002 experiment, there was a great deal of within-replicate variability in growth (fish were individually marked so that growth measurements were made on each fish). Thus, no significant differences in growth were seen between the treatments. Proximate analysis of fillets and carcass showed no significant differences in percentages of protein, lipid, or ash among the treatments, nor were there any differences in moisture content. Similarly, there were no significant differences in carcass weight, fillet weight, liver weight, fillet yield, hepatosomatic index, or viscerosomatic index among the
treatments. Because of the growth variability, fish in each tank were divided into sub-populations (those above vs. below mean growth increment for the tank) for further regression analysis of growth vs. all of the variables mentioned above. The results yielded many significant relationships, although few generalizations can be made based on protein:lipid composition of the diets. The only striking result of this analysis was that fish in the no-current treatment exhibited no significant regressions. The protein:lipid portion of this project was completed by August, 2003. Work on the next phase of the project, plant protein substitutions for fish meal, has been delayed until 2004, due to delays in the enrollment of a new graduate student and in the completion of our new aquaculture research facility.
Impacts
Fish feed manufacturers may want to increase the lipid levels in diets for summer flounder, depending on their willingness to accept our experimental results including a large amount of growth variability among individual fish for each of the diets we tested.
Publications
- No publications reported this period
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Progress 01/01/02 to 12/31/02
Outputs
This project was in its first year in FY2002. The goal for the year was to examine protein:lipid requirements under conditions of optimum current velocity. An existing recirculation aquaculture system, which was originally built to test effects of multiple current velocities on summer flounder growth and survival, was modified so that only one current velocity (15 cm/sec) plus a control treatment with no current velocity are now provided and buffering and filtering capacities have been increased. We worked with personnel at Kansas State University to formulate and produce small quantities of extruded diets (necessary due to the high lipid content of some diets) to be tested. A batch of summer flounder was obtained from a commercial provider and was being acclimated over an extended period to feed on pellets within our experimental system when a very unusual power outage led to the unfortunate demise of the fish. Because no more summer flounder of an appropriate size
were available, we were forced to collect fish from the wild and acclimate them first to captivity, then to pelleted diets. As a result of the extended nature of that process, the first three-month feeding trial began only in September, 2002, and was completed in December, 2002. In this experiment, we compared growth and food conversion ratios (FCR) of fish fed a) a 50% protein, 10% lipid diet in a 15 cm/sec current (C50:10), b) a 40% protein, 20% lipid diet in a 15 cm/sec current (C40:20), and c) a 40% protein, 20% lipid diet in no current (NC40:20). Overall, there were no significant differences in growth or FCR among the treatments; however, that was primarily due to the high variability within treatments. Oddly, fish in the NC40:20 treatment showed the most growth and lowest FCR (although not significant), which was contrary to our previous findings on optimum current velocity. Because fish were individually marked, we were able to discern that the poorer growth in the "current"
treatments (C50:10 and C40:20) was due to 50% or more of the fish in each replicate actually losing weight during the experiment, whereas the majority of fish in each replicate of the "no-current" treatment gained weight. Thus, our results were hampered by growth variability both of fish within replicates and of replicates within treatments. Protein and lipid contents of fish tissues are currently being analyzed.
Impacts
We may be able to replace some protein by adding more lipid to summer flounder diets, thereby reducing the cost of those diets.
Publications
- No publications reported this period
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