Effects of Salinity on Eggs, Larvae, and Juveniles of Blacknose Silversides from Lake Chapala, Mexico

Abstract

AbstractThe salinity tolerance of eggs, larvae, and juveniles of blacknose silverside Chirostoma promelas was investigated with the objective of optimizing hatchery practice. A high proportion (>90%) of eggs became eyed in all salinities. Eggs exposed to an instantaneous change of salinity hatched best at 0–15 practical salinity units (psu; 1 psu ≈ 1‰); reduced hatching occurred at 20 psu and no hatching occurred at 25–35 psu. By contrast, eggs exposed after 5 d to a slow change of salinity to freshwater over 48 h also hatched well at 0–15 psu, but they hatched at higher salinities as well. Fungal infections of eggs were greatest at 0 and 5 psu. Larvae exposed to an instantaneous change of salinity (0–25 psu) had the best survival rates at salinities of 0 psu (83%) and 5 psu (87%), but lower survival was obtained at 10 psu (49%) and 15 psu (22%) after 144 h. At 20 and 25 psu, larval mortality was 90% and 100%, respectively, after 48 h. In contrast, larvae exposed to a slow change of salinity over 48 h showed a higher salinity tolerance (43% survival at 20 psu), although higher salinities killed the fish. Juveniles had a high tolerance (100% survival) to a slow salinity change over 48 h at 0–25 psu. After 90 d, survival was best at 5–20 psu, optimal growth occurring at 5, 10, and 15 psu. Mortality was 100% in fish reared in freshwater after 75 d of culture, possibly a result of the high stress at this salinity. The osmolarity of muscle tissue of juveniles was not significantly different (P > 0.05) between trials, indicating efficient internal ionic regulation at all salinities. The wide salinity tolerance of blacknose silverside is clearly beneficial for its management and culture.