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Nursery Rearing of Macrobrachium Rosenbergii (de Man) Using Hapa-nets : Effects of Stocking Density

M.J. Alam
Freshwater Station, Bangladesh Fisheries Research Institute, Mymensingh-2201, Bangladesh

M.A. Mazid
Freshwater Station, Bangladesh Fisheries Research Institute, Mymensingh-2201, Bangladesh

D.A. jahan
Freshwater Station, Bangladesh Fisheries Research Institute, Mymensingh-2201, Bangladesh

M.E. Hoq
Freshwater Station, Bangladesh Fisheries Research Institute, Mymensingh-2201, Bangladesh

Abstract/ Executive Summary:

An experiment was conducted in two phases for 45 days each to study the effects of six stocking densities (phase-1: 100, 200 and 300 PL/m² and phase-11: 250, 500 and 750 PL/m²) on growth and survival of Macrobrachium rosenbergii postlarvae (PL) in nylon hapa-nets (1.8 m x 1.8 m x 1.4 m) installed in a pond. Stocking densities of 100, 200 and 300 PL 10/m² resulted in similar (P < 0.05) body length (47- 48 mm) and survival rate (84 - 88%), while body weight (0.62 g) in PL with 300/m² was significantly lower than that (0.70 g) in PL with 100 and 200/m². The growth (body length 47 mm and weight 0.64 g) and survival (84%) of PL stocked at 250 PL/m² density were significantly higher (P < 0.05) than that of PL at 500 and 750/m². Besides the variation in growth and survival in PL at six test stocking densities, a sharp increase in body weight of PL was observed beginning at the 4th week of rearing.

Keywords: M. rosenbergii, Stocking density, Hapa-net

Location: Freshwater Station, Fisheries Research Institute

Start Date: 00-00-1997

End Date: 00-00-1997

Program Area: Animal Health and Management

Commodity: Prawn

Objectives:

To optimize the stocking density of prawn PL, aiming at resulting in higher survival and growth, in hapa-net nursery system.

Methodology:

Preparation and installation of hapa-net- Nine nylon hapa-nets of 0.3 mm mesh size measuring 1.8 x 1.8 x 1 .4 m³ each ·were installed in a 0.4 ha pond at the Freshwater Station of Fisheries Research Institute, Mymensingh. During hapa installation, the pond was under carp culture and as it was not possible to make the pond complete drained-out and sun-dried due to periodical raining, most of the fishes were harvested by repeated netting. Monoammonium sulphate (21-0-0) and lime were applied in a 1 :10 ratio at the rate of 1 .5 kg/decimal. Underground water was supplied through central drainage system and the water depth ranged from 85 - 90 em during the study period. Only bamboo poles were driven into the pond bottom and used to make the supporting frame for hapa-nets. The upper and lower corners of each hapa-net were fastened with bamboo poles in such a way that the nets remained suspended in the water column without touching the pond bottom about 10 em above the pond bottom. At each hapa-nets, a few dry coconut leaves were positioned horizontally in the water column to serve as shelters as well as substrates for the prawn PL. A feeding tray (1.2 m x 1 .2 m) made of plastic mosquito screen sewn to a wire frame was provided with each hapanets. Stocking of PL - Phase-/ : Three stocking densities such as 100, 200 and 300 PL/m² were assigned in a randomized block design with three replications for each. Ten-day old M. rosenbergii PL were collected from a nearby prawn hatchery and transported to the pond site using· oxygenated plastic bags. The PL were acclimated to pond conditions and stocked at 17.00 h in the hapa-nets according to the assigned densities. The initial body length (BL) of 9.6 mm and body weight (BW) of 8 mg were recorded by random measuring of PL (n = 1 00). Phase-II : Three stocking densities of 250, 500 and 750/m² of M. rosenbergii PL 12 (BL = 10.5 mm and BW = 9 mg) with three replications for each were tested. Transportation and stocking procedures were similar to that followed in the Experiment I. Feeding to PL - The prawn were fed with a commercial shrimp feed (Saudi-Bangla nursery feed-1 and 2) at the rate of 25% of body weight during 1st week, 15% during 2nd week and 10% during rest of the culture period. The amount of feed was adjusted based on the estimated progressive gain in total biomass and observations of leftover feed on feeding trays. The daily ration was equally apportioned into two feedings: one at 8.00 h and another at 17.00 h. The feed was spreader on the feeding trays, which were hung close to the bottom of hapa-nets. The feeding trays were washed thoroughly prior to each feeding. Data recording and analysis - For the estimation of increment in growth, total BL (from tip of the rostrum to end of the telson) and BW of randomly sampled prawn (n = 50) were measured from each hapa-nets once in a week. The survival rate was estimated finally at the end of study by direct counting. Water quality parameters i.e. temperature, dissolved oxygen (DO), pH, ammonia and alkalinity were recorded weekly using a HACH Kit (Model FF-2). The water quality parameters were within the acceptable limits for prawn culture in ponds. The growth and survival data were subjected to a one-way analysis of variance (ANOVA) and Duncan's Multiple Range Test (DMRT) at 5% level of significance using a PC equipped with statistical package (Statgraphics, Version 4.0).

Source of Information: Bangladesh J. Fish. Res., 1 (1) : 09-16, 1997

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

The results of the present study show that nursery rearing of M. rosenbergii postlarvae in hapa-nets at densities as high as 300/m² may offer benefits of rearing of sufficient numbers of post larvae to allow them to grow to a desirable stocking size and to survival, and to faster turnover for both the hatchery and nursery operators. The present study also indicates the possibility of holding and rearing prawn post larvae, either produced in hatchery or caught from nature in late season (September - October), at high stocking density over the winter period for stocking at the beginning of the next grow-out season.

Knowledge Management: Journal