The acute effect of cortisol implant on self-feeding activity of rainbowtrout Oncorhynchus mykiss (Walbaum)

摘要

Forty-two rainbow trout Oncorhynchus mykiss (Walbaum) (253-629 g) were held individually at 15 deg C in tanks equipped with computer-controlled self-feeders and their feeding activity recorded. After 14 days, a cortisol implant (7.9 percent w/w; dose 91.3 mg kg~(-1)) was injected intraperitoneally into half the fish, and the other half was sham injected. After implantation, the self-feeding activity of the fish was observed for a further 6 days. Feeding activity was reduced in both groups, but the activity of the cortisol-treated rainbow trout was 42 percent higher than that of the sham-injected group. Thus, in the short term, the self-feeding activity of rainbow trout may be influenced by plasma cortisol. Under acute stress, the plasma cortisol concentrations of fish increase rapidly. Recovery of feeding has been reported to occur within hours or days after acute stress (Schreck, Olla & Davis 1997). If the duration of stress is extended, the stress response may become maladaptive, and elevated cortisol levels have been reported to be accompanied by reduced growth (Barton, Schreck & Barton 1987). This may be a product of depressed feeding (Pickering, Pottinger & Christie 1982) and/or increased metabolic rate (Morgan & Iwama 1996). Chronic plasma elevation of cortisol has been shown to suppress feed intake of juvenile rainbow trout Oncorhynchus mykiss (Walbaum) (Gregory & Wood 1999). We studied the impact of cortisol implants on acute self-feeding activity in rainbow trout.