Effects of Ammonia and Ammonium on Tolerance and Byssogenesis in Perna viridis

Individuals of the commercially important green mussel Perna viridis (Kuriakose and Nair, 1976) were exposed to different concentrations of ammonia (NH,) and ammonium (NH',), to determine their reactions with reference to tolerance and byssogenesis.Eight concentrations of ammonia, ranging from 2.75 to 33.00 mg 1-l, and 7 concentrations of ammonium, ranging from 5.00 to 75.00 mg I-', were tested.Young individuals in the size range 20 to 24 mm shell length, collected from an unpolluted rocky shore, were used as test organisms.The 96-h lethal concentration causing 50 O/O mortality (LC 50) was 7.60 mg 1-I for NH, and 13.00 mg 1-' for NH+,.For ammonia, the difference between LC 50 values at 48 and at 96 h is drastic.In sublethal concentrations P. vlndis retarded or suspended pedal-gland activity.A sharp reduction in the number of threads produced occurs at 5.50 and 8.25 mg I-' of ammonia.At higher concentrations the byssus threads secreted displayed reduced rates of tanning and hardening.The difference in the number of byssus threads produced at various ammonia concentration was highly significant.Compared to controls the discs developed at the tips of the byssus threads did not possess normal adhesive properties.