SECTION C: CANCELLED WORK PLANS

REPRODUCTION CONTROL

8RCR1D has been cancelled. The completion of 8RCR1D was dependent on two factors: identifying the best tilapia strain to use for androgenesis and the development of androgenesis techniques that would produce sufficient numbers of viable animals to allow the establishment of YY brood populations. No strain evaluated in 8RCR1A had a high enough percentage of spawns conforming to a 50:50 sex ratio to justify its use in 8RCR1D. Lines of fish conforming to a 50:50 sex ratio inheritance will need to be established from single pair spawns, assuming that sex ratio is an inheritable trait. The heritability of sex ratios needs to be confirmed and is addressed as part of the Ninth Work Plan.

Techniques to produce YY males through androgenesis as part of 8RCR1B are in the development stage and are not ready to be scaled up to produce the large quantities of fish required for 8RCR1D. Results of 8RCR1B demonstrate the difficulty of producing androgenotes. Mortality is increased at three levels: 1) artificial propagation; 2) gamete treatment; and 3) increased homozygosity and androgenotes, increasing the lethal/detrimental genomic combinations. The spawning process to obtain viable tilapia eggs is problematic; only 2.4% of the androgenetically treated eggs hatched, with 0.9% of the treated eggs yielding viable fry to swimup. Refinements of both spawning and androgenesis techniques are needed before adequate numbers of YY fry will be available for estrogen feminization. Finally, the proposed estrogenic treatment would add yet another layer of mortality. This proposed feminization of a genetically inferior progeny group of YY males is not achievable at the present time.

KENYA RESEARCH

8KR2 has been cancelled. This study was undertaken in support of another Eighth Work Plan study, 8RCR1. The intent was to conduct a minimum of 50 pair spawns using pure Oreochromis niloticus vulcani from Sagana Fish Farm, obtain a minimum of 100 fry from each, and determine the sex ratios of those progeny. Over 50 pair spawns were conducted at Sagana during 1997 and 1998, but there was such poor survival of the 5-cm size fry that no set of progeny contained the required minimum of 100 fry. In mid-1998 it was determined that the strain of tilapia being cultured at Sagana was not a pure population of O. niloticus vulcani, but rather a mix of O. niloticus vulcani and O. spirulis. It was determined that continuing to conduct pair spawns with contaminated strains of tilapia was of little value.