DIET, PREY SELECTION AND THEIR ENERGETIC RELATIONSHIP TO REPRODUCTIONIN THE TROPICAL HERRING HERKLOTSICHTHYS QUADRIMACULATUS IN KIRIBATI, CENTRAL PACIFIC

Herklotsichthys quadrimaculatus (gold-spot herring) is a short-lived t ropical herring (maximum age 1 yr) that matures at 5 mo and spawns con tinuously thereafter. It forms an important component of the tuna bait fish catches in Kiribati, Central Pacific, but fluctuates widely in nu mbers. We examined diet and prey selection in the field to determine t he influence of diet on reproduction and to see whether fluctuations i n spawning activity were related to changes in the diet or prey availa ble. H. quadrimaculatus is a particulate-feeder that feeds mainly at n ight, actively selecting both larger high-calorie zooplankton taxa and larger individuals of other taxa. The composition of the diet varied over the 2 yr of the study in relation to variations in the abundance of the main zooplankton taxa and not in relation to spawning activity. Fish of both sexes approaching sexual maturity ate more high-calorie prey (Teleostei and Caridea) than younger fish. This shift in diet wou ld have a selective advantage for short-lived species, enabling them t o continue growing rapidly while developing gonads. The energy content of muscle, gonads, and Liver was examined in female H. quadrimaculatu s at all stages of gonad development. There was no difference in the t issues, which had a mean content of 22.7 +/- 0.3 kJ g(-1) dry wt. The energy content of the liver was positively related to the energy conte nt of the gonads but not to the mean dietary energy intake. The mean e nergy content of the gonads and the mean daily energy intake were inve rsely related, probably due to the body cavity having a smaller capaci ty. The mean daily energy intake was not related to the interval betwe en spawnings or to the proportion of recently spent fish. The mean ene rgy costs of producing an average-sized batch of eggs during peak spaw ning were too high to be obtained only from surplus intake. Both the l iver mass and energy content declined in spent fish, which suggests th at energy stored in the liver was mobilized during periods of frequent spawning. These results are consistent with recent findings that the spawning frequency of temperate clupeids is related to the animal's nu tritional status.