Condition cycles in juvenile Pagrus auratus

Nutritional condition was measured in juvenile snapper Pagrus auratus (<200 mm fork length) using three indices: relative condition index ( I c ), hepatosomatic index ( I H ) and digesto‐somatic index ( I D ). In a laboratory starvation experiment, all three indices declined substantially over a 24‐day period, but I H was most sensitive. In wild snapper I c and I H showed no diel cycles. I D for 0+ snapper showed a strong diel cycle consistent with continuous feeding during daylight hours and lack of feeding during the night. I D for 1+ snapper showed no diel cycle. Subsequent analyses were restricted to daytime samples for I H and morning samples for I D to minimize the confounding effect of time of day. I c , I H and I D were monitored at one site at approximately bi‐monthly intervals over a period of 3.25 years. All three indices varied significantly, but only I D and I H displayed seasonal cycles. I D peaked in late summer‐autumn and dropped to a minimum in winter, due to seasonal fluctuations in the feeding rate that probably reflected variations in metabolic and growth rates. I H peaked in autumn‐winter and declined to a minimum in summer, thus lagging 4–6 months behind I D . I H varied significantly among four sampling sites for all five combinations of sampling periods and year classes, whereas I c varied significantly among sites for only one of the five combinations. The Kawau Bay site, which supported the highest density of snapper, had the highest I H for all except one of the combinations. This suggests that juvenile snapper aggregate selectively at sites that provide optimal feeding conditions. However, no relationship was found between I H and growth rate, indicating that better nutritional condition may not translate into faster growth.