| Pond Dynamics/Aquaculture CRSP | Aquanews ~ Summer 2000 |
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Valderrama, Warrington Successfully Defend M.S. ThesesCongratulations to Lee Warrington, who successfully defended his M.S. thesis on 11 December 1999 at Auburn University under the direction of CRSP Reproduction Control researcher Ron Phelps.
The variability in the factors affecting sex ratio of Oreochromis niloticus was studied using pair spawns from the Egypt, Ghana, and Ivory Coast strains during June-October, 1997 and 1998. Sex ratios from 129 progeny groups were determined by microscopic inspections of the gonads. Of the 12, 450 progeny sexed, 54.14% were males, which differed significantly from a 1:1 sex ratio (P < 0.001). Each strain had at least 42% of their spawns differ from a 1:1 sex ratio (P < 0.05). Logistic regression demonstrated the percentage of males produced by the Ghana strain to differ significantly from that of the Egypt or Ivory Coast strain (P = 0.02). Sex ratios from the 129 progeny groups produced a normal distribution (P > 0.45), but did not reflect a binomial distribution (P < 0.01), as would be predicted by a simple monofactorial sex determination process. Therefore, other factors must account for the variation observed in sex ratios. Single spawn sex ratios ranged widely from 16% to 100% males. Chi-square tests revealed weak correlations between strain and progeny gender, individual parent and progeny gender, as well as, male-female parent combinations and progeny gender. Sixty-five percent (11/17) of the repeat spawns by the same pairings produced sex ratios that extended beyond a range of 10%. The continuous range of sex ratios within the normal distribution suggested the presence of several minor sex-modifying factors in Oreochromis niloticus. Diego Valderrama successfully defended his M.S. thesis on 1 May 2000 at University of Arkansas at Pine Bluff. He is continuing to work as a Research Assistant with Carole Engle, CRSP Marketing and Economic Analysis researcher, who also served as his thesis advisor.
An economic analysis of shrimp aquaculture in Honduras was conducted through the development of two separate models. The first model measured the effect of variability of production factors on the profitability of shrimp operations under different farm scenarios for a given production year (1997). Results of this model pointed out a major potential for profit developed by farms employing an alternative scheme of semi-intensive technologies (AST) characterized by higher feeding rates and water exchange rates. However, data limitations did not allow extrapolation of these results to other production years. To overcome this limitation, a new database was compiled to develop a one-year linear programming (LP) optimization model for each farm-size scenario previously identified. Results indicated that maximization of farm income is achieved by selecting intermediate stocking densities, long grow-out periods, and conservative water exchange rates. In addition, farmers should take full advantage of the superior growth rates characteristic of stocking months such as May and June by concentrating use of resources during this period of the year. The LP models also indicated that, under optimal management conditions, shrimp farms in Honduras have the capacity of producing more than 1,000 kg shrimp tails/ha/year, which implies that superior yields reported by the AST farms are within the reach of the farming capabilities of most shrimp farms in the country. Target MOTAD risk programming models were then developed for each farm scenario to assess the risk inherent to the LP solutions and to identify alternative production plans. However, the LP models indicated that shrimp farms have such a tremendous potential to generate income over critical target income levels that little risk is associated with the formulated optimal plans of activities. Additional simulations were conducted to examine the effects of changing conditions on the profit levels and management strategies selected by the LP models. In general, results of these simulations showed that shrimp farms in Honduras possess the potential to maintain acceptable profit levels under a variety of management situations.
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