Changes to the histological gill structure and haemolymph composition of early blue swimmer crab Portunus pelagicus juveniles during elevated ammonia-N exposure and the post-exposure recovery

Abstract

It is yet unclear whether sub-lethal ammonia-N levels cause irreparable damage to aquatic crustaceans, or if recovery is possible, the potential factors involved. The aim was to investigate the effect of 0.706 and 2.798mmol L1 ammonia-N exposure on the haemolymph osmolality, Na1, K1, Ca21, pH, ammonia-N, total haemocyte counts (THC) and gill histopathology of Portunus pelagicus juveniles at 0, 3, 6, 12, 24 and 48 h respectively. Following 48 h, crabs were transferred to pristine seawater allowing a recovery period up to 96 h and similarly measured. In addition moribund crabs, induced from lethal ammonia-N levels of 7.036 and10.518mmol L1, were measured for haemolymph osmolality/ions and pH levels. The results demonstrate that despite severe gill damage within 6- and1h of 0.706 and 2.798mmol L1 ammonia-N exposure, respectively, no significant change (P40.05) in the haemolymph osmolality, Na1, K1, Ca21 or pH levels occurred or by ammonia- N-induced morbidity. Although the gills can completely recover within 24 and 48 h post exposure to 0.706 and 2.798mmol L1 ammonia-N, respectively, likely facilitated by significant haemocyte increases (Po0.05) within the haemolymph and gill lamellae, dependent factors were the previous ammonia-N concentration and recovery duration while individual variability was also noticed.