Population growth, trophic level, and reproductive biology of two congeneric archer fishes (Toxotes chatareus, Hamilton 1822 and Toxotes jaculatrix, Pallas 1767) inhabiting Malaysian coastal waters

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=aLb) 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.

Morphometric and meristic variation in two congeneric archer fishes Toxotes chatareus (Hamilton 1822) and Toxotes jaculatrix (Pallas 1767) inhabiting Malaysian coastal waters

A simple yet useful criterion based on external markings and/or number of dorsal spines is currently used to differentiate two congeneric archer fish species Toxotes chatareus and Toxotes jaculatrix.Here we investigate other morphometric and meristic characters that can also be used to differentiate these two species.Principal component and/or discriminant functions revealed that meristic characters were highly correlated with pectoral fin ray count,number of lateral line scales,as well as number of anal fin rays.The results indicate that T.chatareus can be distinguished from T.jaculatrix by having a greater number of lateral line scales,a lower number of pectoral fin rays,and a higher number of anal fin rays.In contrast,morphometric discriminant analyses gave relatively low distinction:76.1% of fish were ascribed to the correct species cluster.The observed morphometric differences came from the dorsal and anal spines lengths,with T.chatareus having shorter dorsal and longer anal spines than T.jaculatrix.Overall,meristic traits were more useful than morphometrics in differentiating the two species;nevertheless,meristics and morphometrics together provide information about the morphological differentiation between these two closely related archer fishes.