The effect of gradually decline of salinity on haemolymph parameters of adult shrimp Litopenaeus vannamei (Boone, 1931)

The present study was conducted to evaluate the effects of salinity levels (40, 35, 30, 25, 20,15, 10 and 5‰) on haemolymph parameters and survival of adult shrimp Litopenaeus vannamei. Shrimps were distributed in fiberglass tanks containing water with 40‰ salinity then salinity was gradually declined during 7 days at rate of 5‰ a day by adding clean fresh water. Haemolymph of three shrimps was daily sampled from each treatment in triplicates. The haemolymph parameters including total haemocyte count (THC), total plasma protein (TPP), differential haemocyte count (DHC) were measured. Significant differences were found between treatments in terms of THC values (p<0.05). The highest THC were observed in shrimps exposed to salinities of 25 and 5‰ (p>0.05) versus the lowest THC was measured in 35‰ one. No significant difference was found in TPP levels between examined salinities (p>0.05). Hyaline cell composed 67.8 to 68% of THC (31.4 × 106 ± 0.79 × 106 cell ml-1), but those of semi-granular and granular cells were 1.8 to 2% and 29.4 to 30%, respectively. Both semigranular and granular cell counts were significantly lower in group 10‰ throughout the experiment period. However, hyaline cells count was found to be lower in shrimps exposed to 30‰, 25‰ and 20‰ salinities (p<0.05). The semi-granular cells showed higher values in shrimps exposed to salinities of 30‰ compared to other treatments (p<0.05). In salinities of 5‰ and 10‰, the values of granular cells were the lowest. It is suggested that a declining rate of 5‰ in salinity of water per day conducting for adaptation of L. vannamei could be appropriate to the shrimp, since THC and TPP levels can be recovered every 7 days through the salinity change.