Effect of administering sustained-release thyroxine microparticles on reproductive performance and egg quality in tilapia (Oreochromis mossambicus) broodstock

Abstract

Biodegradable sustained-release microparticles containing thyroxine (T4) were developed to study the influence of hormone manipulation on broodstock reproductive performance and the quality of their eggs. Female tilapia (Oreochromis mossambicus) were injected with either microparticles containing T4 (2.5 μg g-1 body weight) or an equivalent amount of blank microparticles. The administration of sustained-release T4 microparticles generated a large increase in serum T4 levels soon after injection (day 2); this was followed by a gradual decline in serum T4, but the level remained significantly higher than in the controls during the 20-day study period. Significantly higher T4 levels in eggs and newly hatched larvae were also observed in the groups from females injected with sustained-release T4 microparticles compared with those injected with blank microparticles. However, no significant differences were observed in the spawning intervals, egg number per spawn, egg diameter, or percentage fertilizability and hatchability. Morphometric examination of the newly-hatched larvae revealed that in the group of females injected with T4 microparticles, the mean total length and the standard length were significantly increased, whereas no clear effect was observed in other parameters such as yolk area and eye diameter. These data indicate that manipulation of the T4 hormone level in broodstock through sustained release did not affect the reproductive performance significantly, but resulted in an improvement in the quality of their eggs as shown by the significantly larger larvae at hatch.