Temperature tolerance and metabolic depression of a convict cichlid under the influence of enhanced ultraviolet-A (320-400 nm) irradiation.
The effects of increased (5%) sub-lethal UVA irradiation on the total metabolism of a sub-tropical convict cichlid (Cichlasoma nigrofasciatum) were examined. The specific oxygen consumption (Vdot over˜o2) from 23 to 35°C was measured to determine the tolerance limits for environmental temperature. The experiment covered 2 generations (G1 and G2) of inbred-derived populations. The fish were measured at different stages of development covering the period before and after maturation. The fish were grown at and adapted to a temperature of 27-29°. The group that was grown under increased UVA irradiation since hatching (G2UVA) developed general metabolic depression at all temperatures. The metabolic depression was especially expressed after the fish reached maturation. No metabolic depression was observed in the non-irradiated control groups(G2-control and G1-control) nor in the mature fish of the G1-UVA group, which had been grown under increased UVA irradiation from 4 months of age. Vdot over˜o2 increased with increasing temperature, reaching a maximum at 31-33° for the G1- and G2-control groups. For the G1-UVA group, a small peak of Vdot over˜o2 was obtained at 29° reaching its maximum level at 33°. For the G2-UVA population, a maximum Vdot over˜o2 was reached at 33° for the young and mature fish and at 29° during maturation. It is concluded that the accumulation of UVA irradiation from early life was responsible for the metabolic depression. It is suggested that the wider temperature tolerance observed in the G2-UVA population is due to a reduction in total metabolic activity.