Growth, survival, haemolymph osmolality and organosomatic indicies of the Western King prawn (Penaeus latisulcatus Kishinouye, 1896) reared at different salinities

Abstract

The western king prawn (Penueus Zarisulcutus) is one of the most economically valuable species of crustacean in Australia. The experiment was carried out for 60 days to determine the growth, survival, haemolymph osmolality and organosomatic indices of the western lung prawn (2.95 f 0.26 g mean initial weight) reared at 10, 22, 34 and 46 g L of salinities. In addition, haemolymph osmolality and osmoregulatory capacity (OC) of the western king prawn (5.37 f 0.1 g mean initial weight) reared at salinities (10, 22, 34 and 46 g/L) were determined following 7, 14 and 21 minutes of air exposure and compared with the brown tiger prawn (P, esculentus). Mean final weight, total length, carapace length and specific growth rate (SGR) of the western king prawn were highest at a salinity of 34 g/L. Moult increments (in weight and total length) of the western king prawn were not significantly different (P > 0.05) when reared at four different salinities. Food conversion ratios were lowest in prawns reared at salinities of 22 and 34 g/L. Survival of the western king prawn was highest at a salinity of 22 g/L and lowest at a salinity of 10 g/L. Haemolymph osmolality of the western king prawn increased with an increase in salinity and weight. Isosmotic points of the western king prawn calculated from regression lines between haemolymph and medium osmolality were 28.87, 29.46 and 31.73 g / L at 0, 20 and 60 days of rearing (accordingly to 2.95 f 0.26; 4.02 f 0.47; 5.79 f 0.64 g body weight), respectively. Tail moisture content of the western king prawn decreased with the increase of salinity. After 60 days of rearing, the lowest hepatopancreas moisture content of the prawns was at a salinity of 22 gL. Wet weight and dry weight hepatosomatic indices of the prawns were highest when reared at a salinity of 22 gL.Wet weight and dry weight tail muscle indices of the prawns were highest at a salinity of 34 gL. Isosmotic points of the western king prawn were 33.79; 33.29; 32.75 and 33.10 g/L at 0, 7, 14, and 21 minutes of air exposure, respectively. Isosmotic points of the brown tiger prawn were 30.89; 31.89; 32.09 and 31.07 g/L at 0, 7, 14, and 21 minutes of air exposure, respectively. Air exposure reduced OC of both the western king prawn and brown tiger prawn. OC of both species at a salinity of 10 giL was reduced significantly after 14 minutes of air exposure. Twenty-one minutes of air exposure did not change OC of the western king prawn reared at salinities of 22, 34 and 46 g/L. OC of brown tiger prawn reared at 22 g/L decreased after 21 minutes of air exposure while OC of the brown tiger prawn reared at 46 g/L decreased after 7 minutes of air exposure. The results indicate that both species spent less energy on osmoregulation at 34 gL salinity than at other salinities. The results suggest that the optimum salinity for rearing of western king prawns ranges from 22 g/L to 34 g/L. Salinities of 10 and 46 gL are unsuitable for rearing brown tiger prawns and salinity 10 g/L is unsuitable for rearing western king prawns. Furthermore, a salinity range from 30 g/L to 32 gL is suitable for the culture of brown tiger prawns.