Genetic parameters for reproductive traits in female Nile tilapia (Oreochromis niloticus): I. Spawning success and time to spawn

Breeding programmes for Nile tilapia typically use nested mating designs with 2 females mated to 1 male to produce paternal half-sib families. This mating design can take up to 3 months or longer to produce the desired number of half-sib family groups. Prolonged family production increases common environmental effects, and negatively affects estimation of genetic parameters. In this paper we investigated the hypothesis that prolonged family production is a consequence of selection for growth in Nile tilapia. We compare two mating systems: group mating with 7 males and 15 females (MM) and group mating with a single male and 10 females (SM), using females from generation 12 of the GIFT sub-strain kept at RIA-2, Vietnam. Spawning success was modelled as a threshold trait (SPAWN) using a linear repeatability animal model and a generalised logit linear repeatability model. All animals that spawned before 32 days were labelled 'spawn' (1) and animals that did not spawn after 32 days were considered as 'no-spawn' (0). We then changed the threshold and estimated heritability at each threshold point; e. g. with a threshold at 20 days, all animals with 'spawn' records after 20 days are considered 'no-spawn'. Overall, the MM experiment yielded a higher proportion of successful spawn records than the SM experiment. However, in both experiments 85% of the successful spawns were produced within 20 days. In the SM system, males frequently mated with more than one female during a mating period of 4 days. Heritability estimates for SPAWN were 0.20 to 0.22 for linear model and 0.14-0.18 for logit model with thresholds from 20 to 32 days. Estimates were consistent between linear and logit models. Estimates for 'time to spawn' were not different from zero (0.01 +/- 0.02). Genetic correlations of SPAWN with harvest weight ranged from 0.48 to 0.52 for thresholds of 20-32 days. We conclude that Nile tilapia favour mating in groups and that spawning success as defined here is a heritable trait. Selection for harvest weight in GIFT should improve spawning success of Nile tilapia, provided the mating period is limited to 20-32 days. To facilitate the rapid production of paternal half-sibs, we recommend using a group mating design with single males and multiple females in a single tank. (C) 2013 Elsevier B. V. All rights reserved.