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Rematuration of Hatchery Used Wild Spawners of Macrobrachium Rosenbergii (de Man 1879) in Captive Condition

Nani G. Das
Institute of Marine Sciences and Fisheries, University of Chittagong, Bangladesh.

Mohammad M. Monwar
Institute of Marine Sciences and Fisheries, University of Chittagong, Bangladesh.

Mohammad L. Siddique
Institute of Marine Sciences and Fisheries, University of Chittagong, Bangladesh.

Abstract/ Executive Summary:

Successful rematuration and spawning of hatchery used wild spawners (Broodstock) were conducted in the green house of Niribili Hatchery at Cox’s Bazar, Bangladesh. After first spawning, ten healthy female spawners having length and body weight ranges of 18.0-22.0 cm and 90.9-105.1 gm respectively were directly stocked (one per each tank) in ten circular fiberglass tanks of 500 L capacity. In addition to first spawning in the maturation tanks, a total of three repeat spawnings were observed from the rematured spawners. Gonadal condition of the experimental spawners (n=10) was fully spent for eight individuals and partially spent for two individuals during stocking in the rematuration tanks. Of all the spawners, 100% spawned for second time, 80% spawned for third time and 50% spawned in the fourth time. Total number of eggs laid by the ten spawners was 60.4x10⁴, out of which fertilized eggs and larvae obtained were 57.5x10⁴ and 49.5x10⁴ respectively in the first spawning, the corresponding rates of fertilization and hatching being 95.05% and 85.08%. In first repeat (rematured) spawning, the total number of eggs and larvae produced by ten spawners were 52x10⁴and 37x10⁴ and fertilization and hatching rates were 92.76% and 76.89% respectively. Observations limited to the 10 prawns studied indicate that while the fertilization rate of eggs was almost uniform, hatching rate gradually decreased with each consecutive spawning. The recovering spawners were maintained under controlled environmental conditions of water temperature (28.05 ± 0.15 ^oC), salinity (12.0 ± 0.10 gL^-1) and DO (6.5±0.05 ppm), and fed on fresh frozen meat of squid, clam, cockle, and crab as well as a combination of those items, at 15% (wet weight) of their body weight, crab meat (97.79%) being the most preferred feed consumed during their rematuration.

Keywords: Macrobrachium rosenbergii, Rematuration, Repeat spawning, Gonadal maturation, Eggs,

Location: Cox’s Bazar, Bangladesh

Start Date: 00-00-2011

End Date: 00-00-2011

Program Area: Variety and Species

Commodity: Prawn

Objectives:

To find out if rematuration of used wild spawners of M. rosenbergii in captivity to facilitate more seeds for stocking, as availability of wild broodstock is likely to be a problem in future.

Methodology:

The experiment was carried out in a commercial hatchery, at the Niribily Hatchery Ltd., situated at Kalatali Hatchery Zone, about 5 km south of Cox’s Bazar City in Bangladesh. Maturation and larval rearing units were set up in the “green house” of the hatchery. 10 circular fiberglass tanks of 500 L capacity each for rematuration and 5 tanks of the same size for spawning and hatching purposes were used. Two rectangular tanks of 10 metric tones (MT) each were used for water storage and treatment. Fresh seawater of 30-35‰ was pumped through a submersible sand filter placed at the sub-littoral zone in the sea near the hatchery. The pumped seawater was stored initially in the sedimentation tank of 120 MT capacities. After 24 hours of sedimentation water was again pumped to the treatment tanks through sand gravel filter. The filtrate water was treated with 25-30 ppm formalin for six days before use and heated to desired temperature by titanium water heaters. The treated seawater with 28^oC was pumped to the rematuration and spawning cum hatching tanks. The seawater was mixed with freshwater made available from ground water source, to get the desired salinity of around 12‰. Spawners are usually abandoned in commercial hatcheries after first spawning. Ten females having size variation of 90.9 - 105.1 g (mean 98.32 ± 4.08 g) and 10 males of 110.0 - 130.5 g (mean 119.28 ± 5.08 g) of M. rosenbergii were collected immediately after first spawning and the average number of eggs and larvae per spawner was recorded. The spawners were immediately stocked in the rematuration tanks at a stocking density of two individuals (a male and a female) per tank at a ratio of 1:1. The physico-chemical parameters of the water in the rematuration tanks were recorded daily. In the maturation tank, water temperature, salinity, D.O., pH and NO₂-N were 28.05 ± 0.15 ⁰C, 12.0 ± 0.10 gL^-1, 6.5 ± 0.05 ppm, 8.0 ± 0.15 and 0.05 ± 0.03 ppm respectively. No water exchange was done during the first three days of stocking. After that 50% water in each tank was exchanged daily before siphoning of fecal matter. The temperature was kept around 28⁰C with the help of immersion heaters. The spawners were fed with fresh frozen flesh of cockle (Anadara sp.), blood clam (Dosinia sp.), mud crab (Scylla serrata) and squids (Sepia sp.) either singly or as a mixture in accordance with their consumption capacity. Each feed of five items was given daily to the ten tanks (each tank with one male and one female) in randomising way of each successive day during whole rearing period of 30 days. The total body weight of 20 prawns (10 males and 10 females) was calculated as 2,176 g and the daily feed consumed by the individuals was calculated as 326.5 g (average) showing the 15% (wet weight) at four times a day. The uneaten feed was removed daily from the tanks. The rematuration tanks were covered with black polyethylene paper together with ‘orchid sheet’ by at least 90% to minimize the disturbance of the animals. The ovarian maturity was checked daily at the evening by holding them against an underwater flash light beneath the ventral side of the abdomen. Development of eggs was examined with a scoop net. When the color of the eggs became dark grey from yellowish, they were transferred to hatching tank after disinfection with 25 ppm formalin for 90 minutes. Sodium salt of EDTA was added to the hatching tanks at the rate of 2-3 ppm concentration. The water in the hatching tanks was agitated with a stirrer at 10-15 minutes interval until hatching was completed. Egg samples from the spawners and newly hatched larvae were preserved in 5% neutral formalin. At the end of the study, surviving spawners and males were preserved in 10% formalin and the length and weight were taken from the preserved samples.

Source of Information: ABAH Bioflux, 2013, Volume 5, Issue 1. 25-31

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

Both temperature and feed have strong effect on the early gonadal maturation and spawning of M. rosenbergii.

Knowledge Management: Journal