The Nile tilapia (Oreochromis niloticus) is one of the most important aquaculture species groups especially in South East Asia, Africa, South America and China. The gross production of Nile tilapia increases year by year because of the strong worldwide demands for this potential freshwater fish as a food resource for humans. Therefore, further research is necessary for the establishment of the culture technology for this species such as appropriate rearing conditions and feeding technology. The development of self-feeding system has led to a new perspective for future Nile tilapia culture and alternative dietary selection. The purpose of this study is to clarify the feeding characteristics, such as daily feeding pattern and growth performance of Nile tilapia using a self-feeding technique.The self-feeding activity experiment was conducted under two rearing conditions for individual test, insulated room treatments under a controlled light regime (LD 12:12) and constant water temperature (25ºC), and indoor treatments under uncontrolled light regime and monitored water temperature (25ºC) by cooler and heater. For group experiment, the trials were conducted by outdoor treatments under natural conditions which consisted of Experiment one period one (Expt1-P1), Experiment one period two (Expt1-P2), Experiment two period one (Expt2-P1), and Experiment two period two (Expt2-P2). The outdoor treatment was carried out from early summer through late autumn in Mie, Central Japan. Another experiment was conducted to determine whether feeding activities of Nile tilapia are regulated by internal circadian oscillator, the feeding activity of individual Nile tilapia was recorded under controlled light regime and water temperature conditions and within a light-dark (LD) cycle, as well as under constant lightness (LL) or constant darkness (DD) conditions.The results of self-feeding activity experiment showed that the daily self-feeding activity of Nile tilapia in indoor treatments was nearly daytime synchronizing with the given photoperiod (24hr). In outdoor treatments, when the water temperature was between 25-30ºC, the feeding profile showed daytime feeding activity. However, in Expt2-P2, the growth performance diminished when the water temperature dropped below 20ºC and Nile tilapia shifted to a nighttime feeding profile. The results revealed that Nile tilapia has a dualistic capacity for demand-feeding both in light and dark phases. In addition, under the circadian rhythm experiments with a constant environmental condition, one individual showed a free running phenomenon in its feeding activity. The result indicates that the feeding behavior of Nile tilapia is under control of biological clock. Interestingly, the individual showed a circadian rhythm longer than 24 hours (τ=24.4) when it exposed to constant darkness on one hand, it showed a rhythm shorter than 24 hours (τ=23.6) when it exposed to constant lightness on the other. Thus, Nile tilapia seemed to have a dual biological clock system and this circadian system may affect the seasonal change of diel feeding activity synchronizing with the change of natural photoperiod.In growth performance aspects, in indoor treatments, the value of mean specific growth rate (SGR), feed efficiency (FE), and the rate of daily self-service food supply/body weight (BW) were 2.49%/day, 103.23%, and 2.26%BW/day. The results of the SGR, FE, and BW in insulated room experiment were 2.81%/day, 109.67%, and 2.38%BW/day. In group treatments, the highest result of SGR, FE, and BW was in Expt2-P1 with 3.45%/day, 118.90% and 2.62%/BW/day, respectively. The weight gain was significantly greater (P<0.05) in males than that in females in both group experiments.In conclusion, it became clear that Nile tilapia has a dualistic feeding pattern and assumed has a dual system of biological clock relating to the dualistic phase of feeding. In addition, my finding suggested that the self-feeding could be an effective method for the tilapia culture. Moreover, information obtained from self-feeding experiments will enable us to identify the physiological condition of farmed fishes through their expression of appetite. Therefore, we will be able to give to Nile tilapia suitable amounts of feed which best fit the environmental conditions based on this knowledge.
内容記述
本文 / Graduate School of Bioresources Mie University
72p
Studies on the Feeding Behavior and Growth Performance of Nile Tilapia (Oreochromis niloticus) using Self-feeding System
2017DB010
(9.73MB)
