Ecology and biology of the white-tailed Humbug Dascyllus aruanus (Pomacentriade, Pisces) from Minicoy Atoll

Abstract

The poniacentrid Dascyllus aruanus (Linnaeus) lives among tlie branches of ramose corals throughout the Indo-Padfic along with Chromis caeruleus. Though, both the species prefer to be associated with live coials, D. aruanus can easily adapt to dead coral colonies when live corals become scarce in nature due to large scale death of corals as is observed at Minicoy. D. aruanus is observed to attain a total length of 61 mm at the end of the iirst year and a total of 97.0 mm by the end of the second year of life. This may be the maximum length the species attains at Minicoy. The length-weight relationship shows significant difference between the male and female, hence separate formulae has to be used to determine these relationships as follows. Males .. Log W = —3.676976 + 2.480743,Log L. Females .. Log W = -4.243749 + 2.807415 Log L. The sex ratio for the two year periods of observation is Male : Female = 1:1.61 and 1 :1.35 respectively. The size at first maturity at 50 % level is estimated to be 38 mm. Fecundity ranged from 2,125 to 7,157eggs in an ovary at a time. The individual fish spawns more than once in a year. The breeding season almost extent throughout the year with an active period from April to January. The pelagic phase of the larvae seems to last about 2 weeks. The behaviour and biology of the two co-existing species viz. D. aruamts and Chromis caeruleus display very little difference indicating both species have evolved almost similar adaptations