| In this study, the effects of temperature, salinity, dissolved oxygen, ammonia-N, nitrite-N on the molting of Scylla paramamosain were investigated, and all the results are as following.Under the conditions of salinity of 20‰, pH 7.5-8.5, Scylla paramamosain which were about to molting were put into seawater with seven temperatures (10℃, 15℃, 20℃, 25℃, 30℃, 35℃and 40℃) to identify the effects of temperature on the molting of Scylla paramamosain. The results showed as follow: The temperature had no obvious effect on the increase of carapace width, carapace length and weight (P>0.05). 25℃-30℃was the best temperature range for the molting of Scylla paramamosain(p<0.05), and the molting rate could reach 77.77%. 20℃-35℃was the feasible temperature range for molting(p<0.05). If the temperature below 15℃or above 40℃, Scylla paramamosain could not molt. For the Scylla paramamosain which have not molted, at the temperature range of 15℃-35℃, there were a high survival rate. For the Scylla paramamosain which have molted successfully, 30℃-35℃was the suitable temperature range for Scylla paramamosain surviving, but 20℃-25℃was not good enough and with a low survival rate. When the temperature was 30℃, Scylla paramamosain needed the least time to finish the molting process, and Scylla paramamosain needed less time to molt at the temperature range of 25℃-35℃. Scylla paramamosain which have molted successfully could survive for the longest time at the temperature range of 30℃-35℃. As a whole, Scylla paramamosain could survive at the temperature range of 15℃-35℃, and could molt at the temperature range of 15℃-35℃, 25℃-35℃was the suitable temperature range for Scylla paramamosain molting and 30℃was the optimum temperature.Under the conditions of DO>5mg/l, PH7.5-8.5 and temperature of 27～30℃, Scylla paramamosain which were about to molting were put into seawater with eleven salinities(0, 5, 10, 15, 20, 25, 30, 35, 40, 45 and 50‰) to identify the effects of salinity on the molting of Scylla paramamosain, and the results showed as follow: The salinity had no obvious effect on the increase of carapace width, carapace length and weight (P>0.05). Within the salinity range of 15～20‰, which was the most optimum salinity range for molting of Scylla paramamosain, and the molting rate was 88.89%, when the salinity was 5～35‰, Scylla paramamosain could molt normally. For the Scylla paramamosain which had not molted, at the salinity range of 15～20‰, there was a high survival rate. For the Scylla paramamosain which have molted successfully, 5～35‰was the suitable salinity range for Scylla paramamosain surviving. The salinity had no obvious effect on the molting time, but could affected the living time of Scylla paramamosain after molting, when the salinity was above 40‰, the living time of Scylla paramamosain which had molted successfully would be shorted obviously, if the salinity was 0 or 50‰Scylla paramamosain would be killed directly. The results suggested that the salinity range of 15～20 was the best for Scylla paramamosain to survive and molt, at the salinity range of 5～35‰, Scylla paramamosain which had not molted would survive normally, but for Scylla paramamosain which had molted successfully, the salinity range is 10～35‰.Under the conditions of salinity of 20‰, PH 7.5-8.5 and temperature of 27-30℃, Scylla paramamosain which were about to molt were put into seawater with different dissolved oxygen(DO) concentration(1mg/L, 2mg/L, 3mg/L, 4mg/L, 5mg/L, 6mg/L and 7mg/L) to identify the effects of dissolved oxygen on the molting of Scylla paramamosain, and the results showed as follow: The DO concentration had no obvious effect on the increase of carapace width, carapace length and weight (P>0.05); With the DO concentration was above 5mg/L, the crabs had higher molting rate, the rate of molting had significant difference between the low DO concentration groups 2-3mg/L(38.89%-50%) and high DO concentration groups 6-7mg/L(77.67%)(p<0.05). If the DO concentration was above 5mg/L, no matter before or after molting, Scylla paramamosain had higher survival rate, when the DO concentration was 7mg/L, the survival rate was higher than any other groups. The DO oxygen had no obvious effect on the molting time of the Scylla paramamosain, but when the DO concentration was 7mg/L, the crabs used the least time to finish the molting proceed. The DO concentration had significant effect on the living time of Scylla paramamosain which had molted successfully, If the DO concentration was above 4mg/L, the crabs could survive for a long time, however, when the DO concentration was lower than 3mg/L, the life activity of Scylla paramamosain would be inhibited, if the DO concentration was lower than 2mg/L, the crabs would die in a short time. The results suggested that within the DO concentration range of 2-7mg/L, Scylla paramamosain could molt successfully, but only when the DO concentration was above 4mg/L, Scylla paramamosain could live and molt in the course of nature, if the DO concentration was lower than 4mg/L, the life activities of Scylla paramamosain were be affected. Under the conditions of salinity of 20‰, PH7.5-8.5, temperature of 27～30℃, Scylla paramamosain which were about to molting were put into seawater with different ammonia-N(0mg/L, 4mg/L, 8mg/L, 16mg/L, 32mg/L, 64mg/L and 128mg/L) to identify the effects of salinity on the molting of Scylla paramamosain, and the results showed as follow: The ammonia-N had no obvious effect on the increase of carapace width, carapace length and weight (P>0.05). When the ammonia-N was below 8mg/L, the crabs could molt normally, however, if the ammonia-N was above 16mg/L, the molting would be restrained, the rate of molting had significant difference between the low ammonia-N groups 0-8mg/L(67%-77.67%) and high ammonia-N groups 64-128mg/L(0-27.67%), if the ammonia-N over 128mg/L, all of the crabs would die in a short time. When the ammonia-N was below 32mg/L, Scylla paramamosain which hadn't molted could survive normally and had a high survival rate, on the contrary, if the ammonia-N was above 64mg/L, the poisonousness of ammonia-N to Scylla paramamosain was very obvious, and only few crabs could survive, when the ammonia-N was below 8mg/L, the crabs which had molted had a high survive rate. The ammonia-N had no obvious effect on the molting time and the living time to Scylla paramamosain which had molted successfully. The results suggested that Scylla paramamosain could survive normally when the ammonia-N was below 32mg/L, if the ammonia-N was below 8mg/L, Scylla paramamosain could molt in the course of nature, however, when ammonia-N was above 128mg/L, the ammonia had a great poisonousness to Scylla paramamosain, and all of the crabs would die in a short time.Under the conditions of salinity of 20‰, PH7.5-8.5, temperature of 27～30℃and DO>5mg/l, Scylla paramamosain which were about to molting were put into seawater with different nitrite-N(0mg/L, 10mg/L, 50mg/L, 90mg/L, 130mg/L, 170mg/L and 210mg/L) to identify the effects of salinity on the molting of Scylla paramamosain, and the results showed as follow: The nitrite-N had no obvious effect on the increase of carapace width, carapace length and weight (P>0.05); The rate of molting had significant difference between the low nitrite-N groups 0-50mg/L(66.67%-83.33%) and that of high groups 90-210mg/L(0-33.33%), when the nitrite-N was below 50mg/l, the crabs could molt normally, however, if the nitrite-N was above 90mg/l, the molting would be restrained, if the nitrite-N over 130mg/L, no crab could molt successfully. When the nitrite-N was below 50mg/L, Scylla paramamosain which hadn't molted could survive normally and had a high survival rate, on the contrary, if the nitrite-N was between 130mg/L and 170mg/L, the poisonousness of nitrite-N to Scylla paramamosain was very obvious, and only few crabs could survive, however, if the nitrite-N was above 210mg/l, the crabs would die in a short time. When the nitrite-N below 50mg/L, the crabs which had molted had a high survive rate. When the nitrite-N was 10mg/L, Scylla paramamosain had the highest molting rate and survival rate. The nitrite-N had no obvious effect on the molting time and the living time to Scylla paramamosain which had molted successfully. The results suggested that Scylla paramamosain could survive and molt normally if the nitrite-N was below 50mg/l, when the nitrite-N was 10mg/L, Scylla paramamosain had the highest molting rate and survival rate, however, when the nitrite-N was between 130mg/L and 170mg/L, only few crabs could survive and no crab could molt, if the nitrite-N was above 210mg/L, all of the crabs would die in a short time. |
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