" Age and Growth Though Scale & Otolith, Maturation and Fecundity of Some Common Snappers, Lutjanus Lutjanus and Lutjanus Johnii (Family Lutjanidae) In Pakistani Waters with Special Reference of Distribution on Sindh Coast"

Abstract

The coastal belt of Pakistan is about 1,050 km long, divided in to two regions Northwestern region (Balochistan and Makran coast, have 800 km long coastline which extending from Hub River to north west of Karachi with a narrow continental shelf), Southern region (Sindh coast having 250 km long). In the present study two members of family Lutjanidae .i.e. Lutjanus lutjanus and Lutjnaus johnii were collected on monthly basis in respect of their biology, age and growth, population dynamics parameters and distribution along Sindh coast during three years (2005-2007) from main fish markets and boat collections by trawl and gill net from creek system. Collections brought to laboratory at University of Karachi on monthly basis, samples were identified, length (TL in cm), weight (in gm), scales, otolith and gonads of each specimen were examined and data was recorded. About 30 samples of gonads were selected after visual observation, maturity of gonads and values of Gonad somatic index (GSI) were studied which shows spawning season of both species, the relationship between fecundity and somatic weight (gm) and length (TL cm) were studied that’s seems to be the large fish produced maximum eggs in compression of small one. Length –weight relationship of both species shows strong correlations, for the determination of age the growth ring were observed from otolith section which is more reliable in compression to whole otolith and fish scale. The opaque zones from sectioned were studied through marginal increment analysis, shows on opaque zone delineated per year in both species and the rings found on scales were also studied, the results shows the maximum age 11 years of Lutjanus lutjanus at 27.5 cm (TL) and Lutjanus johnii 22 years with 75.5 cm (TL). Length at age data best fitted to Von Bertallanfy Growth Function (VBGF) to obtained the curve, shows the both species are slow growing in large size. Relationship between fish length (TL in cm), fish weight (in gm), fish length (TL in cm) vs otolith radius (mm), fish length (cm) vs otolith weigh (mg) were determined through regression analysis. The length frequency data was used as put in FiSAT II (version 1.2.2), FAO stock assessment tool software for determination of population dynamics parameters .i.e. Asymptotic length (L∞), growth constant (K), mortality (total mortality, fishing mortality and natural mortality), recruitment pattern, virtual population analysis (VPA), probabilities of capture, yield per recruit Y/R and B/R and growth performance indices. The results showed that the exploitation rate of small size fishes were fished by gill net fishing and mortality estimation showed that the both species have not been over harvested in coastal area of Pakistan, high recruitment pattern found in primary growth season, both species are not exploited above the maximum sustainable yield. The results shows that both species are lived in similar habitat and widely distributed along the coastal belt of Sindh, Lutjanus lutjanus are offshore coral reefs and trawling grounds frequently encountered in large schools with other Lutjanus species and trawled to depth of almost 100 m, feed on fishes and crustaceans Lutjanus johnii are frequently found in coral reef while adult and juveniles found in mangrove estuaries, feed upon fishes and benthic invertebrates including shrimps, crabs and cephalopod.