Age and Growth of mottled grouper, Mycteroperca rubra (Bloch, 1793), off Southeast Brazil

Abstract

The mottled grouper, Mycteroperca rubra (Bloch, 1793), is a commercially-important demersal fish in Southeast Brazil, inhabiting rocky and sandy substrates of the outer shelf and upper continental slope. Age, growth and natural mortality of that species were studied by means of the scale-reading in152 specimens of both sexes, with total length ranging from 25.0 to 73.4 cm, in the period from June, 1999 through May, 2000. Scales were found to grow on na isometric proportion with fish length [L = 4.2 + 79.9 S (r= 0,976; P<0,01)], there being an annual periodicity in age ring formation, which takes place on November-December. Back-calculated mean total lengths ranged from 20.0 cm (age group I) to 72.3 cm (age group X). The growth equation in length (cm) is L_t=105.1 [1-e ^{-0.106 (t+1,99)}], wich was represented as weight (kg) by W_t=14.0

[1-e^{-0.106(t+1,99)}]^2,958 obtained through the weight/length regression equation In W = -11.132+2.958 In L (r = 0.993;  P<0.01). The annual natural mortality coefficient was 0.248. The mottled grouper has a low growth coefficient (K=0.106), high growth performance, ᶲ=3.068, a high M/K ratio = 2.34 and a great longevity (t_max=30.3 years), biological features which are typical of carnivorous fishes of the fourth trophic level.