| Aquaculture/Fisheries Center Research Highlights |
| Baitfish (2007) |
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The Effects of a
Dairy/Yeast Prebiotic on Growth and Health of Goldfish (Carassius auratus) We conducted a 10-week feeding trial to determine the effects of standard or high-fat diets with or without Grobiotic-A, a dairy/yeast prebiotic, on performance of juvenile goldfish (2.5 g average individual initial weight) in tanks. There were no differences in average individual weight gain, feed conversion ratio, or survival among diets. Mortality of fish exposed to A. hydrophila was tracked for 4 weeks. Mortality increased over time, but there were no differences among diets. The Use of a Dairy/Yeast
Prebiotic on Golden Shiners in Ponds – Effects on Fish Performance
and Production Economics We evaluated the performance of juvenile golden shiners in ponds fed a control diet or the same formula with 2% Grobiotic®-A, a prebiotic. Golden shiner juveniles (0.1 g) were stocked into 0.04-ha ponds and fed to satiation twice daily (4-7% body weight) with custom-made 35%-protein diets for 7 weeks. At harvest there were no differences in average fish weight, net yield, or feed conversion ratio between treatments. After harvest, 100 fish per pond were moved to indoor tanks for acclimation prior to a bacterial challenge with Flavobacterium columnare. Half of the fish were stressed by crowding prior to the challenge. Stressed, challenged fish fed the diet with prebiotic had higher survival than fish fed the diet without prebiotic, and the higher cost of the prebiotic diet appears justified. Lysine Nutrition in Golden
Shiners A feeding trial is in progress with golden shiners using purified casein-gelatin diets and crystalline amino acids and graded levels of lysine (0.0, 1.0, 1.5, 2.0, 2.5, 3.0, and 3.5 mg/kg diet). Golden shiners (0.8 g initial individual weight) were stocked at 30 fish per 110-L tank in each of four tanks per diet in a recirculating system. Fish have been fed twice daily to satiation for fourteen weeks. So far, there were no differences in growth or survival of fish among diets, and no definitive signs of lysine deficiency. The growth rate is very slow and it is possible the salt (3 g/L) added to reduce stress also reduces growth, and/or that golden shiners do not use crystalline amino acids as well as intact proteins. Nutrient Management in
Commercial Baitfish Ponds The objective of this research is to develop fertilization recommendations leading to the establishment of desired bloom densities in ponds while avoiding unnecessary or excessive applications of nutrients. Analyses of the upper 5-cm of pond bottom sediments in shallow, middle and deep locations within each of 25 commercial baitfish ponds in Lonoke, Arkansas, found that Ca, Mg, Mn, K, Na, S and Cu concentrations were very high (upper 10%) relative to values reported in the literature for freshwater aquaculture ponds. Ground waters from wells into the alluvial aquifer used in filling 14 commercial ponds were analyzed, as were concurrent pond water samples obtained 24-96 h after filling commenced. In comparing the source well waters to resulting pond waters, there were significant differences in the average concentrations of various parameters. For example, phosphate decreased from 0.60 to 0.13 mg/L, and dissolved inorganic nitrogen (DIN) increased from 0.35 to 2.09 mg/L. Results suggest the contribution of the bottom sediments to DIN and likely chemical processes within the filling ponds, such as precipitation of phosphorus. Algal bioassays using natural plankton assemblages were conducted by spiking triplicate 250-mL flasks (water volume of 50 mL) from 16 newly-filling ponds with 0, 1, or 2 mg/L of N and 0, 0.25, or 0.50 mg/L of P. Results as determined by fluorescence and chlorophyll a extraction indicated that addition of phosphorus (0.25 or 0.50 mg P/L) was required for maximum phytoplankton bloom development while the N requirement was variable, ranging from 0 to 2 mg/L. Nitrogen fertilizers have become increasingly expensive, and results imply that for some ponds, no additional nitrogen is required for phytoplankton bloom development. Nine commercial ponds were monitored over the growing season to document bloom density and stratification patterns. Daily stratification as determined by temperature and oxygen profiles and temperature loggers at 3 depths was seen to occur by the end of July and disappear in September. The literature indicates that development of anoxic bottom sediments favors P release into the water column and this could be a factor contributing to the extremely heavy algal blooms seen in many commercial ponds during the summer months. Developing Hatchery
Management Techniques for Fathead Minnows Fathead minnows are typically produced using the spawning-rearing pond method, which provides little control over fish sizes. New indoor hatchery methods now provide fathead minnow fry for stocking. This study was conducted to examine the relationship through regression analysis between initial fry or final fish densities and production parameters. Rosy red fathead minnow fry (1-3 d) were obtained from jar hatching of sodium sulfite-removed eggs and stocked volumetrically at densities of 49, 198, 346, 495 and 643/m2 in 10, 5.9 m2 continuously aerated, plastic-lined pools. Stocking rates were equivalent to 0.2 - 2.6 million fry/acre. Fish were fed daily with a prepared minnow feed, sampled at 3-week intervals, and harvested after 81 days. Survival ranged from 19.7 to 57.7% and was not related to density. Mean fish weight per pool decreased logarithmically with final fish density (R2 = 0.953). Yield generally increased with initial stocking density (Power function, R 2 = 0.846). While results from pool studies should be extrapolated with caution, at stocking densities equivalent to 2.0 million fry/ha and above, yields were in the range of 1,000 to 1,500 kg/ha. These results suggest that large quantities of small fathead minnows can be produced by stocking of fry. However, the economics of this alternate culture system remain in question. Effect of Temperature on
the Growth of Golden Shiners Control of fish size is critical to baitfish production and marketing, and temperature is a major factor affecting fish growth. Temperature-dependent growth models were developed for juvenile golden shiners. Two 10-week trials were conducted in a flow-through aquaria system to determine the growth response of two sizes (0.5 g, 1.0 g) of juvenile golden shiners to temperature. Four temperature treatments (15, 20, 25, and 30°C) were randomly assigned to twenty, 110-L glass aquaria. Quadratic equations were derived to predict maximum growth rates for total weight (DW g/d) and length (DL mm/d) from temperature. Maximum weight gain under study conditions was obtained at 26.0°C for 0.5 g fish and at 24.1°C for 1.0 g fish. Maximum growth in length was obtained at 26.0°C for the 0.5 g fish and at 23.9°C for the 1.0 g fish. Documenting the relationship of temperature to growth could lead to improvements in baitfish farming techniques. A combination of pond and tank culture would make it possible to extend the growing season or stockpile quantities of different sized fish to meet market requirements. Effect of Fish Density on
the Growth of Golden Shiners in an Outdoor Flow-through System Fish density is considered an important factor in fish growth. Many species of cyprinids (and other schooling species) occur in dense populations with growth rates much lower than the potential for that species. A 5-wk trial was conducted in a flow-through outdoor aquaria system to determine the growth response of juvenile golden shiners to increasing density with availability of natural food. Fifteen golden shiners (average wt of 0.32 g per fish) were stocked into each of 18, 110-L aquaria. A 1 mm2-mesh tank divider confined the fish to 100%, 50% or 25% of total tank water volume (96-L), creating initial loading rates of 0.05, 0.09, and 0.19 g/1,000 cm3 (6 replicates per density). Each aquarium received a constant inflow of water from an adjacent pond at a rate of approximately 3700 ml/min (1 gallon a minute), equivalent to a total water exchange every 30 minutes. Fish were confined to the portion of the tank closest to the water inflow. Fish were fed 1% of their body weight once a day with 45% protein flake meal. Fish were harvested after 36 days. Survival averaged between 92-97%. Fish in the 100% treatment grew larger than fish in the 50 and 25% treatments. Loading rates at harvest averaged 0.3, 0.5 and 0.9 g/L in the 100%, 50% or 25% treatments, respectively. Fish in the aquaria were more densely loaded than in culture ponds. No effect on fish final condition (Wr) was observed among treatments. For the ranges of densities tested, golden shiner growth was better in the 100% treatment compared to the other treatments. When growth in the outdoor system was compared to growth in a similar indoor system, fish daily growth rate in the outdoor system was twice the growth in the indoor system for all the treatments. Golden Shiner Growth in
Aquaria with Access to Fractions of Natural Foods The absence of natural food is often cited as the reason that fish in indoor systems do not grow well, but no work has been done to prove or disprove this hypothesis. Preliminary testing was done with an experimental system designed to test the growth of golden shiners in pond water containing the full complement of natural foods (raw) as compared to water that has been filtered to remove large zooplankton (100-micron) and water filtered through a 10-micron mesh to remove all zooplankton and most algae. Eighteen aquaria, each with corresponding bag filter housing, were supplied with pond water containing natural foods from an adjacent fertilized pond. Testing found that zooplankton could be pumped from the pond through pipes and filters into aquaria and remain alive. Water flow into each aquarium could be maintained at the target of 3.7 L/min with frequent cleaning of filter bags. As expected, the smaller mesh clogged more frequently than the larger mesh and there were no problems with the raw (no-filter) treatment. By-pass of zooplankton around the filter bags was discovered, and gaskets and self-sealing filter bags will be used to eliminate this problem.
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