Abstract:
Giant Freshwater Prawn (Macrobrachium rosenbergii) is an essential crustacean
species in culture-based fisheries of Sri Lanka. Studying the morphometric characteristics
and empirical models in fishing and aquaculture is highly beneficial; thus, it is the
most accurate way of analyzing growth patterns. The present study aimed to establish
the length-weight relationship and compute the relative condition factor for the
M. rosenbergii cultured in trophically different perennial reservoirs in Sri Lanka,
considering the trophic status of the reservoirs. The allometric coefficient and condition
factor of M. rosenbergii concerning the trophic state of the reservoir were empirically
ascertained from the samples collected from twenty-five dry-zone perennial reservoirs
of Sri Lanka. Carlson’s Trophic State Index (TSI) was calculated based on the
chlorophyll-a content. The allometric coefficient and relative condition factor were
computed using the total length and weight of the M. rosenbergii. The TSI ranging
between 44.09±0.47 and 65.15±0.24 differed significantly (p<0.05). Sexual dimorphism
in the growth of males over the female M. rosenbergii was ascertained with the aid
of allometric coefficient (b value) 3.2306 (positive allometric growth) and 2.9534 (negative
allometric growth), respectively. In eutrophic perennial reservoirs, Giant Freshwater
Prawns showed the highest allometric coefficient in both sexes. There was a positive
correlation between the allometric coefficient and TSI among males, r(23)=0.7210, p<0.001,
and combined sexes, r(23)=0.7900, p<0.001, respectively. The results of the present study
revealed that the trophic state of the reservoir influences the allometric coefficient
and condition factor of M. rosenbergii cultured in perennial reservoirs of Sri Lanka.
