Feed Intake and Growth of Juvenile Silver Trevally at the Southern Limit of Their Distribution

Abstract

Silver trevally (Pseudocaranx dentex), also known as striped jack or shimaaji, is farmed intensively in Japan (Watanabe et al., 1990) where it can reach 1 kg after 2 years (T. Takeuchi, pers. comm.). Growth rates in Australasian waters are unknown, although data from New Zealand fisheries suggest that juveniles are moderate to fast growing in the wild (Stewart and Grieve, 1993). This study was conducted to obtain information about the influences of temperature on feed intake and to assess growth performance in order to evaluate the aquaculture potential of silver trevally at the southern limit of their distribution in Australia. Juvenile silver trevally caught using a beach seine between April and June 1995 at Stieglitz Beach, Tasmania (142°19'E; 41°20'S) were maintained at the Taroona Marine Research Laboratories. Prior to the experiment described here the fish had been used in a feed experiment for 12 weeks. Diet did not have a significant effect on growth (Gardner, 1998) and the fish were fed commercial feed for 3 weeks before the present experiment. Ration was 2% BW/day over the 15 weeks. Seventy-four fish of mean [SE] weight (37.0 [12.3] g) were randomly allocated to each of three 4 m tanks supplied continuously with unfiltered seawater. Fish were maintained indoors at ambient temperature (16.7 °C decreasing to 12.8 °C) and salinity (31–34‰) under a L8:D16 photoperiod for 112 days (23 January to 14 May 1996). A commercial salmon feed (Gibson’s Ltd, Tasmania: 52.0 (0.01) % crude protein; 13.0 (0.12) % crude fat; 11.8 (0.07) % ash; 21.0 kJ/g GE) was fed to satiation by hand four times per day and total feed intake (g) recorded daily. Wet weight (W, g) and fork length (L, cm) were measured at the start and after 56 and 112 days. Fulton’s condition factor (K) was calculated as 100 3 (W/L). Specific growth rate was calculated for wet weight (SGRW) and fork length (SGRL) as SGR (%/day) 5 100 3 [(ln X2/ln X1)/t]