Abstract:

The photogradient method was used to study the phototactic behaviors of Nile tilapia (Oreochromis niloticus ) during five different growth stages:Ⅰ30.0~45.2mm; Ⅱ51.0~63.3mm; Ⅲ70.0~83.0mm; Ⅳ88.0 ~102.0mm; Ⅴ108.0~120.0mm,which was exposed to the white light at six different lights luminance 250lux、500lux、1000lux、2000lux、4000lux、8000lux. The results showed that the phototactic index(Ip) of five different group Nile tilapia increased with the boosted light intensity which the range was 250lux～1000lux,and the Ip reached the maximum when the light intensity was 1000lux.There was no significant difference in Ip between 250lux and 500lux(P>0.05), but the Ip showed significant difference between 250lux and 1000lux(P<0.01).When the intensity was above 1000lux, the Ip decreased with the increase of light intensity. No significant difference was found in Ip between 2000lux and 4000lux(P>0.05).However, there was significant difference in Ip between 2000lux and 8000lux(P<0.01). In the experimental conditions(water temperature was 23～25℃), the Nile tilapia of I group showed the most obviously phototactic response. The Ip decreased with the growth of Nile tilapia, and the Ip were Ⅰ> Ⅱ> Ⅲ> Ⅳ> Ⅴ. The most preferred light intensity region of tilapia is 1000~2000lux, and it can be used to lure Nile tilapia to the concentrated area, for improving the feeding rate of Nile tilapia and playing an active role in light-purse fishing.