| A series of experiments had been conducted on Red Tilapia, then analyzed and discussed the effect of environmental factors on a series of indicators of the growth of red tilapia, survival, feed utilization ratio and sex ratio. In the latter part of the experiment, red tilapia were farmed in an ecologically controllable intensive breeding system. The results are as follows:1. Within temperatures of 20.5～39℃, six different sources groups of red tilapia had been bred in different temperature gradient range with other optimal conditions for 30d. Then all the fishes were continuously fed at 27±1℃ for 40d. There came the findings:the male rate rose with increasing temperature when it was above 32.5 "C. Effect of masculinization got to the highest 97.3% and male rate was 95% when it was 37±0.4℃. The offspring survival rate was 97%(P<0.05) when it was 27.5℃ while the rate fell below at 37℃. The survival rate almost equaled to zero at the temperature of 39℃. According to the growth curve of red tilapia,27～35℃ were the best growth temperature for young red tilapia. At 30.5℃ the young grew fastest but when it was 30.7℃, the young got the maximum biomass.2. In 0,15,30%o three salinity gradient experiments had been made about red tilapia and Nile tilapia species reciprocal cross test at 29±0.5℃. The results showed that: when (?) Nile Tilapia×(?) Red Tilapia was in 0‰, the offspring got the best rates in weight and specific growth, respectively 37.06±0.40g and 4.87±0.39%/d (P>0.05); Not only have the highest heterosis (H%),40.34% (WG) and 23.17%(SGR) under such condition but feed conversion ratio was as low as 1.75, significantly lower than other hybrid progeny of different salinity, having the best breeding results(P<0.05).3. Setting 24,28,32℃ three temperature gradient, then 0,8,12%o three salinity gradient and 7,7.5,8 three pH gradient, orthogonal experiment, after feeding 60d, the results indicated that:temperature is a major factor that impact the growth rate of red tilapia offspring, temperature, salinity and pH effect it’s growth significantly (P <0.01). When there are temperature 32℃, salinity 0%o, pH 7.0, red tilapia offspring SGR could attain to 3.14%/d, while the feed conversion ratio (PER) is up to 67.70% at pH 7,5. Under the condition of temperature 32℃, salinity 8%o, pH 8, verified by experiment, red tilapia offspring survival rate was 98.3%(P<0.05). Similarly, proved by experiment, the male rate of red tilapia offspring was 63% under the contions of temperature 32 ℃, pH 8, salinity 12‰ (P>0.05).4. It is feasible that red tilapia can be farmed in an ecologically controllable intensive breeding system. When the experiment came to an end, it was easily seen that:the overall weight of red tilapia was on the rise in an upward tendency. At the beginning of the experiment, the initial weight was 15.5±0.43, total weight 19.2kg red tilapia seedlings, after 90d breeding the final body weight was 110.0±2.21g, total weight 134. 2kg, increased 7.0-fold; the survival rate was 98.55%. The pH maintained 7.1 to 8.2 in a downward trend but the ammonia and nitrite were 1.72-6.58mg/l and 0.55～6.0mg/l. They were in an upward trend. Water quality is good and stable, red tilapia grows normally. |
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