Progress 10/01/06 to 10/01/07
Outputs
OUTPUTS: Feed-trained largemouth bass fingerlings were held at ambient water temperature and at 35C for six weeks in May and June then held at ambient temperature until reaching a sexable size. Fish held at ambient temperature (28C) had a sex ratio of 50:50 males and females. Fish held at 35C for six weeks had a sex ratio skewed to males (62.5% male : 37.5% female). Based on histology, gonads of 30 d old largemouth bass were not sexually differentiated but by 54 d post-hatch ovarian tissue was apparent in some individuals. To determine the feasibility of manually selecting female largemouth bass, fish were produced intensively, fingerlings trained to a formulated diet and cultured to a range of sizes with the goal of determining the cost of production of manually selected females. Eleven-month old bass were sorted into five size categories and sexed. The accuracy of manual selection was determined for each size category. The costs of production (variable costs only) to obtain fry,
fingerlings, and sexable-size fish was determined. An average of 14,769 eggs/kg female was obtained, resulting in 4,905 swimup fry/kg female at a cost of $4.84/1000. Nursery ponds stocked at 148,515/ha yielded 0.97 g fingerlings with a 95.6% survival, at a cost of $53.53/1000. Fingerlings were stocked into 3 mm mesh net cages, feed trained for 13 days and held an additional 21 days on a commercial diet. At harvest fish averaged 3.53 g with a 61.2 % survival costing $253.03/1000. Fingerlings were stocked into ponds at 20,000 and 40,000/ha and cultured 270 days on a commercial diet. Average weights and survivals at harvest were 179 g and 159 g and 25.3% and 33.7% for the two respective stocking densities. It was possible to sex fish with 100% accuracy when they were 20 cm and larger. Thirty five percent of the total number of bass produced were identifiable females. The cost of production of these females was $5.26/fish when the value of males and unsexable fish at $6.61/kg was deducted
from the total production costs. Hand sexed females have been stocked into farm ponds to produce a trophy bass fishery. Two-year old fish weighing up to 5 lbs have been produced.
PARTICIPANTS: As PIs, R. Phelps, W. Daniels, J. Chappel, R. Wright. Tyler Heep as Masters degree student responsible for the field research.
TARGET AUDIENCES: This project was aimed at farm pond owners interested in trophy bass fishing opportunities on their own land and public land managers interested in providing a more diversified fishing experience. Also targeted were hatchery managers of private and public facilities and extension agents
PROJECT MODIFICATIONS: None
Impacts
A further refinement of techniques is needed to be able to say whether temperature can be a practical tool to radically skew the sex ratio of largemouth bass. Hand sexing to obtain females is a viable alternative as fish of 10 cm and above can be sexed with 100% accuracy. The cost of production of hand-sexed females is within what the market might be able to bear and production costs can be reduced with mass production. The increased demand for trophy bass fishing can be met by the production of all-female largemouth bass. Profitability of private hatcheries can be increased with the adoption of this methodology.
Publications
- Heep T. and R. P. Phelps, 2007. Production of all-female largemouth bass for trophy bass fishing. Alabama Fisheries Association Meeting, Orange Beach AL. Heep T. and R. P. Phelps, 2007. Costs of producing all-female largemouth bass for trophy bass fishing. Southern Division of the American Fisheries Society, Memphis TN.
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