Efeito do fotoperíodo no crescimento e sobrevivência da tilápia do Nilo Oreochomis niloticus, linhagem chitralada, durante e após a reversão sexual

Abstract

The work studied the effects of photoperiod in the growth and survival of the tilápia, Oreochromis niloticus, Chitralada strain, during and after the sex reversion. The experiment was carried through in the Station of Continental Aquaculture Prof. Johei Koike, of DEPAq - UFRPE, in the period of dezembro/2006 junho/2007. The study it occurred in two stages. Stage I was becomes fullfilled during the sex reversion: 611 after-larvae (W = 0.031±0.0058g e L = 1.2±0.096cm) had been distributed in aquariums contend 1.5 after-larvae /L. The fish had been submitted the six photoperiods treatments: (0L, 8L, 12L, 16L, 24L) and has controlled (natural light: 12.5L), L = light, each group I contend two repetitions. The fish had been fed with commercial ration of 45% CP, contend 60mg of the hormone 17-á-metiltestosterone/ kg. The daily meal was based on 20% of the total biomass, distributed in four meals. A biometric was carried through in the end of the experiment, or either, in 28° day. One surveyed the oxygen dissolved (mg/L), pH and temperature (ºC) two times to the day, beyond analyses of the levels of amonia and nitrit. For analysis of the results ANOVA complemented for the test of Tukey with P£0.05 was used. The after-larvae submitted to fotoperíodos 0L (0.37±0.258g), 12L(0.33±0.295g) 16L (0.38±0.216g) and control(0.34±0.225g) had not differed statistic in the end weight (P>0.05). In relation to the end length, group 0L (2.80±0.550cm) was equal statistic to all the treatments with exception of the 24L. The best survival was of the control (77.44%). Stage II happened after the sexual reversion. fingerlins (W = 0.38±0.16g e L = 2.81±0.40cm) reverted for male had been used. The experimental drawing was equal to the one of Experiment I, except for the stockage density (0.33fish/L). Commercial ration was offered 45% CP, calculated from 10% of the total biomass, distributed in four food/day, until 46° day (end of the experiment). The biometric happened to each 15 days. The results had demonstrated not to have difference statistics (P>0.05) between treatments 8L, 12L, 16L, 24L and control, in relation to the average length weight. However, it was identified that the fish of group 16L ( L = 9.00cm e W = 15.70g) presented bigger values that the too much treatments. The individuals of group 0L:24E, had presented the lesser growth. The survival was superior 80% in all the treatments. Ahead of the results it can be concluded that: Photoperiod intervenes negative with the survival of the after-larvae, but not in the growth. firgerlins I of chitralada tilápia grows faster in long photoperiods, of that in short photoperiods.