Influence of size, variety and male female ratio in the production of tilapia (Oreochromis spp.) eggs in concrete tanks at the venezuelan andean foothills

The aim of this study was examine the effect of the variety, size and male female ratio in the egg production of tilapia Chitralada (CH: Oreochromis niloticus) and Taiwanese Red (TR: O. mossambicus x O. niloticus) reared in tanks of concrete. The study was conducted in a fish farm located at the Venezuelan Andean foothill of Trujillo state, Venezuela. A 2x2x3 factorial arrangement was applied: two varieties (CH and TR), two sizes (small and large) and three sexual relations (1♀: 1♂; 2♀: 1♂; 3♀: 1♂). The data were processed by analysis of variance using the general linear model of the SAS. The CH females produced 1.5 times more eggs, which weighed 1.6 times more and had a fecundity 1.6 greater than the TR (P <0.01). Likewise, tilapia of larger size produced a more volume (7.24 ± 0.70 versus 5.39 ± 0.60 ml; P<0.01) and more egg mass (6.57 ± 0.62 versus 4.74 ± 0. 51 g; P<0.01), and showed a greater relative fecundity (113.8 versus 86.6, P<0.10), than those of smaller size. The male female ratio did not affect any of the reproductive variables studied. The interaction between variety and size indicated that TR tilapia of both sizes exhibited a similar reproductive performance (P>0.05), while large CH females produced a greater egg volume (8.91 ± 0.79 versus 6, 20 ± 0.79; P<0.01) and egg mass (7.99 ± 0.67 versus 5.65 ± 0.67; P<0.01), and were more fertile (1210.5 ± 113,4 versus 911.4 ± 113.5; P<0.10) than the smaller ones. In addition, large CH tilapia were reproductively more efficient than the same category of TR. In CH females the sex ratios did not affect most of the variables studied, with the exception of relative fecundity that was greater in the 2:1 ratio than in the 1:1 and 2:1 (154.4 ± 21, 4 versus 129.9 ± 18.1 and 133.1 ± 14.6 respectively; P<0.01). In contrast, in the TR females that were in a 3:1 sex proportion, the reproductive performance was considerably lower than those that were in a 1:1 or 2:1 sex ratio, and even, their performance was significantly lo