| This study used two equipments which were the outer cage and sediment colletor to design3kinds of cages. Cage A is an usual cage with the escape-proof net. Cage B is a cage with outer cage. Cage C is in accord with cage B with the addition of sediment collector. The growth performance, economic benefit, discharge of nitrogen and phosphorus and water quality index were determined. The results are summarized as follows:1. Comparison of the growth performance and economic benefit of different cages(1) The average weight gain and special growth ratio of channel catfish from cage B and cage C was significantly higher than that of cage A(P<0.05). There was no difference between cage B and cage C(P>0.05). There were significant differences of the daily growth ratio among different cages. The growth of channel catfish was different seasonally (P<0.05). The feed conversion ration of cage A, cage B and cage C was2.31,1.44and1.17, respectively. Cage C had the highest SI and cage B was a little lower. Cage A had a much lower SI than cage B and cage C.(2) In the culture-cycle, the bighead carp and tilapia of cage B and cage C had significantly higher weight gain, daily growth ratio and special growth ratio than cage K(P<0.05). The bighead carp and tilapia in cage K had minus weight gain.(3) Cage B and cage C had higher economic benefit than cage A. The feed and fry cost of three cages represented89.74%>95.33%and94.78%of total cost. The cost of sediment collector represented only0.58%of the total cost.2. The nitrogen and phosphorus discharge of different cages in the culture-cycle(1) The apparent digestibility coefficients of phosphorus for channel catfish from cage A, cage B and cage C were85.14%、79.50%and81.78%and there were no significant differences among them(P>0.05). The apparent digestibility coefficients of nitrogen for channel catfish from cage A, cage B and cage C were92.70%、92.53%and91.22%, and there were no significant differences among them(P>0.05).(2) There were significant differences among total nitrogen growth efficiencies(P<0.05). Cage C had highest total nitrogen growth efficiency and cage B had a lower one. Cage A had the lowest one among them,. There were significant differences of total phosphorus growth efficiencies(P<0.05). Cage B had a significantly higher total phosphorus growth efficiency than cage A and cage C and cage C were higher than cage A, but did not reach significant level(P>0.05).(3) The nitrogen growth of cage C were signifantly higher than cage A and cage B(P<0.01). The fecal nitrogen of cage A was higher than cage B and cage C, but did not reach significant level(P>0.05). The excretory nitrogen of cage A was higher than cage B(P<0.05) and the excretory nitrogen of cage B was higher than cage C(P<0.05). There were no significant differences among absorptive nitrogen of different cages(P>0.05). The nitrogen budget equation of three cages were:Cage A:100CN=20.22GN+7.32FN+72.46EN=7.32FN+92.68ANCage B:100CN=31.59GN+7.50FN+60.91EN=7.50FN+92.50ANCage C:100CN=37.19GN+8.77CN+54.04EN=8.77FN+91.23AN(4)During the culture-cycle, bighead carp from cage B assimilated1.65kg nitrogen and0.67kg phosphorus from the water column and the tilapia assimilated2.09kg nitrogen and0.61kg phosphorus. Bighead carp from cage C assimilated3.45kg nitrogen and1.69kg phosphorus from the water column and the tilapia assimilated1.87kg nitrogen and0.41kg phosphorus. The sediment represented20.25%dry matter,11.12%nitrogen and31.93%phosphorus of the feed.(5) The discharge of dry matter from cage C for1kg feed was66.23%of cage A and73.91%of cage B. The discharge of nitrogen from cage C for1kg feed was66.75%of cage A and81.80%. The discharge of nitrogen from cage C for1kg feed was24.46%of cage A and38.58%.3. Influence of water quality index by cage culture(1) There were no significant differences of the transparency and Chlorophyll a among different cages(P>0.05). The control site had lower transparency and Chlorophyll a than the cages, but did not reach significant level(P>0.05). The transparency and Chlorophyll a had a significant correlation(P<0.01, r=-0.72). (2) The concentration of ammonium nitrogen in the control site was significantly lower than that in the cages(P<0.01). There were no differences of the concentration of ammonium nitrogen among different cages(P>0.05). The concentration of nitrite nitrogen in the control site was significantly lower than that of the cages, but did not reach significant level(P>0.05).(3) The concentration of total nitrogen in the control site was a little higher than that of cage A and lower than that of cage B and cage C, but did not reach significant level(P>0.05). The concentration of total phosphorus in the control site was lower than that of cage A, cage B and cage C, but did not reach significant level(P>0.05). The N/P ratio in the control site was lower than that of cage A, cage B and cage C, but did not reach significant level(P<0.05).The nitrogen/phosphorus ratio is41.09-578.46which is volatile.The concentration of phosphorus and Chlorophyll a had a significant correlation(P<0.01, r=0.50) and the N/P ratio had a significant correlation(P<0.01, r=-0.47). |
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