No abstract

Population growth, trophic level, and some aspects of reproductive biology of two congeneric archer fish species, Toxotes chatareus and Toxotes jaculatrix, collected from Johor coastal waters, Malaysia, were studied. Growth pattern by length-weight relationship (W=aL(b)) for the sexes differed, and exhibited positive allometric growth (male, female and combined sexes of T. chatareus; female and combined sexes of T. jaculatrix) and isometric growth (male samples of T. jaculatrix only). Trophic levels of both species were analyzed based on 128 specimens. The results show that, in both species, crustaceans and insects were the most abundant prey items, and among crustaceans the red clawed crab Sesarma bidens and Formicidae family insects were the most represented taxa. The estimated mean trophic levels for T. chatareus and T. jaculatrix were 3.422+/-0.009 and 3.420+/-0.020, respectively, indicating that they are largely carnivores. Fecundity of T. chatareus ranged from 38 354 to 147 185 eggs for females with total length ranging from 14.5 to 22.5 cm and total body weight from 48.7 to 270.2 g, and T. jaculatrix 25 251 to 150 456 eggs for females with total length ranging from 12.2 to 23.0 cm and total body weight from 25.7 to 275.0 g. Differences in values of gonadosomatic and hepatosomatic indexes calculated for both species in this study may have resulted from uneven sample size ranges.

The size, growth and reproductive biology of the giant mudskipper, Periophthalmodon schlosseri, was studied in the inter-tidal mudflat of a mangrove swamp along a 0.4-0.6 · 5 km stretch of the Sepang coastal waters, Selangor Malaysia. The size ranges of the giant mudskipper specimens caught in the study area were between 10-27.5 cm TL (20.6 ± 3.1 cm) for males and 14.5-28.5 cm TL (21.9 ± 2.3 cm) for females. Male to female sex ratio during the study was 1 : 1.1. The estimated von Bertalanffy growth parameters were L ¥ = 29 cm and K = 1.4 year )1 , with a growth performance index of Ø¢ = 3.1. Otolith microstructure analysis revealed a strong correlation (Female: r = 0.920, n = 35; Male: r = 0.943, n = 41, P < 0.05) between the number of daily rings (number of days old) over the respective size ranges of male (8.5-19.5 cm SL) and female fish (11.8-22.3 cm SL). Four maturity stages were described to follow gonadal development based on external features; these stages were further validated through histological examination of the ovary and oocyte diameter measurements. The gonadal development cycle of P. schlosseri was asynchronous, as marked by the random mixture of early stages oocytes (diameter: 70.7 ± 14.9 lm) to matured stages (356.9 ± 20.2 lm), and had a prolonged spawning season extending from June to October. Monthly fluctuation of the gonadosomatic and hepatosomatic indices for this species was highly correlated (r = 0.126, P < 0.05).

Abstract:In this study we aimed to analyze the effects of water temperature and diet on the length-weight relationship and condition of juvenile Malabar blood snapper Lutjanus malabaricus over a 30-d experimental period. The experiment was conducted in the laboratory using a flow-through-sea-water system. The fish were subjected to four different temperatures (22, 26, 30, and 34 °C) and two diets (commercial pellet and natural shrimp). Fish were fed twice daily. L. malabaricus exhibited negative allometric growth (b<3) at the beginning of the experiment (Day 0) at all temperatures and both diets except for 22 °C fed with shrimp, which showed isometric growth (b=3). Conversely, at the end of the experiment (Day 30) fish showed isometric growth (b=3) at 30 °C fed with the pellet diet, indicating that the shape of the fish did not change with increasing weight and length, and a positive allometric growth (b>3) at 30 °C fed with shrimp diet, which indicated that fish weight increases faster than their length. The rest of the temperatures represented negative allometric growth (b<3) on both diet, meaning that fish became lighter with increasing size. The condition factors in the initial and final measurements were greater than 1, indicating the state of health of the fish, except for those fed on a pellet diet at 34 °C. However, the best condition was obtained at 30 °C on both diets. Nevertheless, diets did not have a significant effect on growth and condition of juvenile L. malabaricus. The data obtained from this study suggested culturing L. malabaricus at 30 °C and feeding on the pellet or shrimp diet, which will optimize the overall production and condition of this commercially important fish species.