Aspects of the reproductive biology of two archer fishes Toxotes chatareus, (Hamilton 1822) and Toxotes jaculatrix (Pallas 1767)

Various aspects of the reproductive biology of two archer fishes Toxotes chatareus and Toxotes jaculatrix were studied to describe gonad development, spawning season, sex ratio, and fecundity. Spawning season was assessed using monthly changes in gonadosomatic index (GSI) and histological inspection of the gonads. Both species exhibit two modes of oocytes; a mode of small primary growth oocytes and a single mode that increases with size as oocytes sequester vitellogenin and undergo maturation, showing the synchronous oocyte development typical of total spawners. Based on GSI values and advanced stages of oocyte maturity, T. chatareus and T. jaculatrix, females appear to spawn from November to December. The average fecundity of female T. chatareus was 55 000 ± 5538 eggs, and T. jaculatrix was 50 000 ± 3440 eggs; fecundity ranged from 20 000 to 150 000 eggs for both species, with relative fecundities of 600 to 1100 eggs/g body weight, and a mean value of 800 ± 32 for T. chatareus; relative fecundity ranged from 500 to 1100 with a mean value of 700 ± 23 for T. jaculatrix. Sex ratio, defined as the proportion of males to females, was 2. 2 and 2. 5 in T. chatareus and T. jaculatrix, respectively. The apparent abundance of males in samples could be due to females being positioned lower in the water column and therefore being sampled less frequently. Our results indicate that in both species, spawning occurs between the months of November and December during the monsoon season, which provides the mangrove coastal waters inhabited by these species with an abundance of food resources and additional floodplain nursery habitat for larvae and juveniles

Energy Allocation in Juveniles of a Warm-temperate Reef Fish

During the first year of life, organisms are faced with competing demands for energy between growth and storage. Most research on energy allocation in young fishes has focused on cold-temperate species which are subjected to strong seasonal fluctuations in productivity, while few studies have considered those at lower latitudes where seasonality is less pronounced. Gag (Mycteroperca microlepis) of the northeastern Gulf of Mexico settle in coastal seagrass beds in the spring as juveniles and emigrate to offshore reefs in the fall. Upon settlement, these young fish grow at remarkably fast rates, but their growth slows considerably before emigration. Slowed growth can be explained by one of three hypotheses: (1) size-specific emigration times; (2) reduced feeding efficiency associated with declines in primary and secondary productivity; or (3) energetic shifts in allocation from growth to storage. Gag emigrate essentially as a cohort, so slowed growth does not result from differential emigration patterns based on fish size. They also emigrate before seasonal declines in primary and secondary productivity; thus, food remains abundant and feeding efficiency constant. The more plausible hypothesis is that there is an energetic shift from growth to storage. The liver serves as the primary site of lipid storage and the hepatosomatic index of juvenile gag increases coincident with reduced growth. The overall effect of increased energy stores is presumably for use during offshore migration and/or for overwinter survival