A PRELIMINARY STUDY OF THE BIOLOGY OF CTENOGOBIUS ORINIGER (C.V.) AND BRACHYGOBIUS KABILIENSIS INGER IN SINGAPORE WATERS

Abstract

1. The study of the biology of Ctenogobius criniger C.V. was begun in May 1969 and discontinued in May 1970 after it was found that it was not possible to find mature specimens even with careful and intensive sampling. The biology of Brachygobius kabiliensis Inger was carried out over two years from May 1970. The study of the taxonomy of the Singapore Gobiinae was carried out at the same time as the above biological studies. 2. 32 species of Gobiinae from Singapore island were collected and examined during the taxonomic study. Of these 22 have been identified to species and 8 to the genus. There are 2 unidentified gobies, including 3 probable new species. Description of the probable new species has been withheld pending further detailed measurements on a larger range of specimens. 3. The ecology of the two habitats at which sampling was carried out – a sandy littoral shore in the case of Ctenogobius criniger and a brackish water river area in the case of Brachygobius kabiliensis – was studied and are discussed. 4. Morphometric studies on the two species gave the following data: Ctenogobius criniger SL:TL – 0.73 to 0.84 for males, 0.75 to 0.80 for females DIL:TL – 0.25 to 0.33 for males, 0.29 to 0.31 for females D2L:TL – 0.39 to 0.47 for males, 0.45 to 0.48 for females AL:TL – 0.43 to 0.49 for males, 0.47 to 0.51 for females HL:TL – 0.22 to 0.26 for males, 0.23 to 0.27 for females. Brachygobius kabiliensis SL:TL – 0.78 to 0.84 for males, 0.76 to 0.80 for females DIL:TL – 0.32 to 0.38 for males, 0.31 to 0.37 for females D2L:TL – 0.43 to 0.47 for males, 0.40 to 0.46 for females AL:TL – 0.45 to 0.51 for males, 0.45 to 0.53 for females HL:TL – 0.28 to 0.33 for males, 0.28 to 0.32 for females 5. The length weight relationship in the two species were found to be: Ctenogobius criniger Juveniles - W =0.00242L2.902 Males - W =0.01258L2.539 Females - W =0.02133L3.127 Combined - W =0.0127L3.063 Brachygobius kabiliensis Juveniles - W =0.008533L3.027 Males - W =0.03916L2.918 Females - W =0.01995L3.134 Combined - W =0.01387L3.261 6. Studies on the relative condition factor (or Ponderal Index) of both species were carried out and are discussed. 7. The population distribution of both species were studied by means of length frequency data and the data were fitted to the von Bertalanffy growth equation to give an estimate of the growth of the fishes under the conditions studied. It was found that Brachygobius kabiliensis showed a polymodal pattern of many broods a year. The pattern for Ctenogobius criniger was less clear but was also polymodal. The catabolic growth constant K, was found to be 0.0016 per day for Ctenogobius criniger and 0.0032 for Brachygobius kabiliensis. The asymptotic standard lengths calculated were 132.5mm and 17.15mm respectively for Ctenogobius criniger and Brachygobius kabiliensis. 8. The sexual behaviour, missing pattern and embryology of Brachygobius kabiliensis were studied. Embryology of Brachygobius kabiliensis was followed in the laboratory after successful artificial fertilization of 22 eggs. The rearing of the hatched larvae was unsuccessful. 9. Studies on the food and feeding habits of the two species gave the following results: Ctenogobius criniger Juveniles - mainly copepods together with smaller zooplankton. Males - adult fish feed on a wide variety of food organisms. Females - and do not show particular preferences between males and females. Brachygobius kabiliensis Juveniles - feed mainly on smaller copepods. Males - the adults do not show particular feed. Females - preferences between sexes but feed on a variety of zooplankton (especially amphipods, copepods) polychaetes, brachyuran larvae.