Abstract:
Abudefduf vaigiensis is a highly exploited reef fish species for the marine ornamental fish industry.
The morphological and histological transitions during the metamorphosis of A. vaigiensis are
important to study their life cycle. Samples are collected from Dodanduwa area in May 2022. The fish
were classified into three size categories, with 10 fish collected for each category. Specifically, the
size categories were Small-SC (less than 9cm), Medium-MC (ranging from 12cm to 15cm), and Large LC (greater than 16cm). Fish were examined to find out the differences in external morphology, gut
composition, and histology in the stomach and intestine. Morphometric parameters (Total Length,
Standard Length, etc.) increased with the body size but the meristic counts were independent of body
size except for the number of transverse bands. Length-weight relationship for MC (ts=2.754,
b=3.934, p<0.05) and LC (ts=4.112, b=5.238, p<0.05) groups depicts allometric growth, while fish in
small size class showed an isometric growth (ts=-1.0214, b=2.893, p>0.05). Fulton’s condition factor
(K) in SC (1.11 ± 0.19) showed significantly better condition of fish compared to that of fish in MC
and LC groups. Individuals from different size stages undergone a difference in pigmentation and
showed more black strips in MC and LC (6 stripes) than in SC (5 stripes). The terminal mouth and
the incisor-type teeth forming a cutting plate indicated scraping feeding habits. Gut component
analysis suggested that larger fish scrape on harder substrates. Relative gut length (RGL) denoted
that gastrointestinal tract undergoes rapid remodeling and the RGL of larger fish (2.83 ± 0.13) was
higher than smaller fish (1.83 ± 0.13). Histological studies revealed that the thickness of tissues in
the stomach and intestine increases with the growth of the fish. This study showed that histological
and morphological changes occur in accordance with the development of A. vaigiensis from juveniles
to adults.
