Effect Of Dissolved Oxygen, Temperature, Salinity, Ammonia-n And Nitrite-n On The Survivoal And Food Intake Of CHARYBDIS FERIATUS

In this study, the effects of dissolved oxygen, temperature, salinity, ammonia-N and nitrite on the survival and food intake of Charybdis feriatus are investigated, all the results are as following.Effects of dissolved oxygen on the survival and food intake of Charybdis feriatus: Under the conditions of temperature of 23℃~27℃, salinity of 30 and pH 7.5~8.5, we put the Charybdis feriatus into seawater with different dissolved oxygen(DO) concentrations(1mg/L~6mg/L), to identify the effect of the DO concentration in seawater on the survival and food intake. The results are as following: The DO cocentration of 1mg/L and 2 mg/L is not suitable for Charybdis feriatus as it shows a low chance of survival, weak vatality and low food intake rate. Under the DO concentration of 4mg/L~6mg/L, the survivorship has no significant difference (p>0.05), but the significant difference appears when the DO concentration is 1mg/L~2 mg/L (p<0.05). The food intake rate of the DO cocentration of 3mg/L is lower than that of the DO concentration of 4mg/L~6mg/L.However, there is not significant difference with between them (p>0.05). The results suggest that the DO cocentration of 3mg/L is a milestones. Above this concentration , the crab shows a higher survival rate and food intake rate, while below this concentration both rates begin to go down. Thus the optimal concentration of DO for the crab to survive and food intake should be higher than 3mg/L.Effects of temperature on the survival and food intake of Charybdis feriatus: Under the conditions of salinity of 30, pH 7.5~8.5 and DO of 6mg/L~6.3mg/L, we put the Charybdis feriatus into seawater with different temperature (5℃,10℃,15℃,20℃,25℃,30℃,35℃and 40℃), to identify the effect of quick and gradual temperature change on survival and food intake. The results are as following: Crabs show the highest mortality, shortest survival time and lowest food intake rate at the temperature of 5℃and below or at 35℃and above. Within the temperature of 10℃~30℃, crabs show higher survival rate and longer survival time. Especially within the temperature of 20℃~30℃, crabs show the highest food intake rate which has a significant difference with other group (p<0.05). The results suggest that crabs can survive within the temperature of 10℃~30℃. The temperature of 20℃~30℃is viable for the crabs, and the optimal temperature is 25℃.Effects of salinity on the survival and food intake of Charybdis feriatus: Under the conditions of temperature of 22℃~28℃, pH7.5-8.5 and DO of 6mg/L~6.3mg/L, we put the Charybdis feriatus into seawater with different sanility (5,10,15,20,25,30,35,40,45,50 and 55) , to identify the effect of quick and gradual salinity change on survival and food intake of the crabs. The results are as following:With a quick salinity change, the survival time of Charybdis feriatus is the longest at salinity levels 20~40 which has a significant difference with other group (p<0.05). With a quick salinity change, the survival rate of Charybdis feriatus is the highest at salinity levels 20~35 which has a significant difference with salinity levels 15 and below or 45 and above (p<0.05), while has no significant difference with salinity levels 40 (p>0.05). There is a significant difference between salinity levels 40 and above or 15 and below with salinity levels 20~35, that thelatter group has a higher food intake rate (p<0.05). There is a significant difference between salinity levels 45 above and 15 below with salinity levels 40 (p<0.05). The results suggest that salinity levels 20~40 is suitable for the crabs food intake. The crabs are fed best at salinity 25~35. The result about the change of weight suggests that: There is a significant difference between salinity levels 40 and above or 20 and below with salinity levels 25~35 which has a lower change of weight (p<0.05).With a gradual salinity change, the survival rate of Charybdis feriatus is the highest at salinity levels 25~40 which has a significant difference with salinity levels 10 and below or 50 and above (p<0.05), but has no significant difference with salinity levels 45 (p>0.05). The survival time of Charybdis feriatus is the highest at salinity levels 20~40 which has a significant difference with salinity levels 10 and below or 50 and above (p<0.05), but has no significant difference with salinity levels 15 and 45 (p>0.05). The crabs are fed best at salinity 25~35 which has a significant difference with other salinity levels. The results suggest that salinity levels 20~45 is suitable for the crabs food intake. The crab are fed best at salinity 25~35.Effects of ammonia-N on the survival and food intake of Charybdis feriatus: Under the conditions of temperature of 23℃~28℃, salinity of 30, pH 7.5~8.5 and dissolved oxygen of 6mg/L~6.3mg/L, we put the Charybdis feriatus into seawater with different concentration of ammonia-N (0mg/L,5mg/L,10mg/L,20mg/L,40mg/L,80mg/L and 160mg/L), to identify the effects of the ammonia-N concentration in seawater on the survival and food intake. The results are as following: Under low concentration group of ammonia-N (0mg/L~40mg/L), crabs show high food intake rate , survivorship and long survival time which has a significant difference with high concentration group of ammonia-N (80mg/L~160mg/L) (p<0.05). The result suggests that the optimal concentration of ammonia-N for the crab to survive and to have a positive food intake rate should be lower than 40mg/L. Crabs show lower food intake rate and higher mortality when the concentration group of ammonia-N exceed 80mg/L.Effects of nitrite-N on the survival and food intake of Charybdis feriatus: Under the conditions of temperature of 22℃~27℃, salinity of 30, pH7.5~8.5 and DO of 6mg/L~6.3mg/L, we put the Charybdis feriatus into seawater with different concentration of nitrite-N (0mg/L,10mg/L,20mg/L,40mg/L,80mg/L,160mg/L and 320mg/L), to identify the effect of the nitrite concentration in seawater on the survival and food intake rate. The results are as following: Different concentrations of nitrite have significant difference on the food intake rate and survivoship.The best condition for food intake and survival is at the concentration of nitrite 0mg/L~40mg/L. When exceeding the concentration of nitrite 80mg/L, crabs show lower food intake rate and higher mortality.