Cage Culture of Lutjanus Johni (Snapper) and Pomadasys Kaakan (grunt) MariCommercial Fishes

Abstract

The objective of present study were to design suitable, cheaper and durable cages, survey suitable sites to place floating cages, and to study growth of juvenile fishes (Lutjanus johni & Pomadasys Kaakan) in cages. The entire coast of Karachi can be separated as, (i) extending from keamari towards Hub River (Balochistan) and (ii) extending from Clifton to the Korangi Creek and to Keti Bunder. Under the available funds and facilities, the primary task of this study was to explore coastal areas nearer to the main city, easily approachable and prove useful to conduct mariculture experiment. The mangrove forests along the Sindh coast were surveyed and expenditure estimates liable to incur to conduct cage culture experiments were made. The mangrove areas along Karachi harbor is found nearer and the estimated cost to conduct cage culture in these areas was relatively lesser than mangrove region along Korangi Creek. Initially mangrove area along Karachi harbour was selected as first site to conduct our experiment. The Jetty along the Marine Academy Mauripur was considered more suitable and easily approachable site. The Director, Marine Academy provided facilities and permission to work at the jetty. The routine weekly hydrographic data from the region (Marine Academy) was taken before starting the experiment. The data however showed pollution, since lot of fishes such as, mullets, grunts, snappers and larvae of other commercial fishes were found in the region, it was decided to place cages at this selected site. The experiment hardly lasted for one month because of, (I) high molarity, pollution being the main cause. (II) High cost incurred in the collection and transport of seed (Juvenile fishes). It was then decided to place the cages towards the open sea. Various sea shores, e.g. paradise point, Hawks Bay etc were surveyed, all these shores were found to be easily approachable by general public creating surveillance problems. Finally the area along Cape Monze under the naval control, restricted for general public was selected. Following types of cages were designed. • One unit of four squared shaped cages, each measuring 1x1x1 meter in length, width and height. Two types of wood, pen wood and Oak woods (Local names) was used; embedded in aluminum frame on all sides. Two types of synthetic nets were used, the outer sides of cages were covered with bigger mesh size net, 3.14 and 2.23cm and inner side with smaller mesh size net 1.44 and 0.8cm. In some cages a bag, made of small mesh size synthetic net was placed inside cage with opening above. This technique proved useful to avoid escape of fish and to protect fish from predators. • Square shaped cage made up of same dimension (1x1x1 m) and the material mentioned above. The cage was covered by metallic net (made of Aluminum fiber) instead of synthetic net. This material was used to avoid crabs and other animal, which tear synthetic fiber net. • Rectangular cage made by hollow PVC pipes 6cm in diameter. This sides of cage measured 2x1x1 m, the net is mounted on the PVC frame, hanging freely with lead weights tied at the bottom of the net. • Rectangular shaped cages 1.2x1x1 m, made of wood (locally called as ‘Dhial’). These cages were made of narrow elongated pieces of wood leaving no room for predators to enter the cage. Synthetic net of mesh size 1.0 cm was used to avoid escape of fishes. All types of cages were lowered in seawater with anchors and tied to floating buoys. Data on durability of cages and the survival rate of fishes was collected during the study. The most useful and durable cage with better fish survival rate was that described as rectangular shaped cage made up of Dhial Wood. Other cages were very often damaged by water currents and needed frequent repairs. The common predators Tetradon sp. (puffer/globe fishes), Murenosox sp. (rock eels) and portunid crabs etc were usually responsible for major damage of cages. In the present set up a unit of cage is a small structure, having 2-4 cages and showed significant impact of seasonal changes (high wind/high currents). Experiments were designed as monoculture setup (Lutjanus johni; pomadasys kaakan and sillago sihama in separate cages); biculture setup (L.johni andP.kaakan in same cage) and polyculture setup (P.kaakan; L.johni; serranus sp. And pomadasys operculare in same cage). Among all of three setups better results were observed in monoculture setup and pomadasys kaakan showed highest production. Biculture of L.johni and P.kaakan also showed significant results. Different stocking densities were used to estimate the total production/total yield in biomass. Finally the results were encouraging; it is suggested that culture of these fishes is practical and will fetch economical gains. Efforts, however, are required to establish hatcheries/nurseries from where young/juvenile fishes could supplied to farmers. Fisherman and fisher-women can stock these two species along protected shores in locally Hand Made cages for few months in order to increase their livelihood and simultaneously increase fish production.