Trophodynamics of the Fish Valenciennellus tripunctulatus. I. Vertical Distribution, Diet and Feeding Chronology

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Abstract
The adult and juvenile life stages of the small (.apprx. 25 mm) zooplanktivorous mesopelagic fish V. tripunctulatus (Esmark) are found at depths of 200-600 m throughout the diel period. Average population density was estimated to be 5 fish (104 m3)-1 and the maximum density recorded was 11 fish (104 m3)-1. Copepods constituted 95% of all food items identified and Pleuromamma was the principal forage genus, contributing 31 and 56% to numbers and biomass of food items, respectively. Ontogenetic changes in diet were observed, the percentage of larger copepods increasing in the diet with increasing fish size. Food items were primarily 1-4 mm in size. The relationship between number of prey in stomachs and fish length was not statistically significant; prey biomass was highly correlated with fish size. A diurnal feeding pattern was apparent, the period of most active feeding being 1200-2200 h. Daily ration, as estimated with regression equations, varied with fish size and increased more slowly in relation to standard length than to fish biomass. Maximum estimated daily ration as a percentage of body weight was 5.6% for 15 mm fish and 3.7% for 30 mm individuals. The average number of prey items in fishes taken during the period of active feeding was 9, while maxima varied between 14 and 24.

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