SEX AND COLOR SEGREGATION IN NILE TILAPIA CROSSES OBTAINED FROM DIFFERENT STRAINS OF YY MALES AND NORMAL XX FEMALES

Noel D. Novelo*, Boris Gomelsky, Shawn D. Coyle, Jeffrey L. Warner,  
 and Alexander G. Kramer
 
 Aquaculture Research Center
103 Athletics Road
Kentucky State University
Frankfort, KY 40601

All-male tilapia production for market size overcomes the disadvantages of mixed sex rearing by increasing meat yield and size uniformity at harvest, and eliminating possibility of uncontrolled reproduction. As global production of Nile Tilapia Oreochromis niloticus continues to rise, ongoing efforts to produce all-male seedstock should be evaluated to improve efficiency, increase profitability, and responsible use of our genetic resources. The YY male technology, a form of genetic sex regulation for production of all-male seedstock, may be considered more acceptable by consumers than hormonally treated fish for human consumption. The goal of this study was to investigate sex and color segregation of commercially available YY males from two sources crossed with three strains of normal XX females.

Broodstock (with ratio of 1 male : 3-4 females) were placed in four independent recirculating tank systems (water temperature 28-29 ºC), fed 0.5 - 1% body weight/day, and females were checked for eggs/fry every two weeks. Putative XY progeny (5 - 7 months old) were placed in 500 mg/L MS-222™; the color phenotype was recorded, and fish were dissected to identify testis or ovary. The percentage of males varied from 88 to 100% (Table 1). The YY males of the same origin could produce different percentages of males in crosses with different female strains. The red color phenotypes in crosses 1 to 3 segregated into two phenotypes: 100% red color appearance (no black pigmentation), and highly variable blotched phenotype (red background color with varying area coverage of dark pigmentation). Cross 4 of two dark lines resulted in dark fish only (Table 1). Additional crosses will be analyzed and comparatively raised as part of an integrated approach for identifying a fast growing red tilapia. The data collected so far show that expression of black pigmentation in fish with red background color is very variable and special studies on investigation of inheritance of this trait are needed.