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Study of the Survival Rate of the Larvae and Post Larvae of Penaeus Monodon (fabricius, 1798) in a Shrimp Hatchery.

Amitosh Sen
ADB Shrimp Hatchery & Training Center, Charpara, Cox’s Bazar, Bangladesh.

Abstract/ Executive Summary:

The survival rate of the larvae and post larvae of Peneaeus monodon was studied in a shrimp hatchery. Observations started from the stocking of nautilus larva (N/4) and continued up to five days old post-larva (P/5) stage in the larvae-rearing tank (LRT). All sorts of management practices were as normal as practiced in a commercial hatchery operation. Average survival rates were found 92.25-74% in proto-zoea, 66.45-53.67% in mysis, 48.37% in P/1 and 41.76% in P/5 stage/ages. The highest mortality was found during the metamorphosis of zoea into mysis, especially during Z/1 to Z/2 (10.31%), than M/1 to M/2 (8.8%), respectively and the lowest was during M/3 to P/1 (5.35%).

Keywords: Larvae, PL stage, Sub-stage, Conversion, Metamorphosis, Survival rate.

Location: ADB Shrimp Hatchery & Training Center, Cox’s Bazar district, Bangladesh

Start Date: 01-03-2004

End Date: 30-04-2004

Program Area: Animal Health and Management

Commodity: Shrimp

Objectives:

To observe the survival rate of P. monodon larvae and PL in a hatchery.

Methodology:

Main considerations of the study were as follows: (1) Size, shape and depth of larvae rearing tanks (LRT) - Two sizes of LRT (RCC structure with marine apoxy paint coating) were used to conduct the study. The size one was elongated with a total capacity of 9 m³ and maximum utilization capacity of 8.5 m³. and the size two was circular with a total capacity of 6 m³ and maximum utilization capacity of 5.5 m³. Both types were one meter in height. (2) Seawater and fresh water - Seawater was collected directly from the Bay-of-Bengal by an underground pipeline from the sea to the hatchery. The salinity of the seawater was 29%. Fresh water was collected regularly from the underground source of tube well (salinity was 0%) within the hatchery premises. Both seawater and fresh water were separately treated by 12-ppm caporite power (60% active chlorine) in the reservoir tank, then de-chlorinated by aeration and sunlight, filtered by slow-sand-filter and one micron filter bag before use. (3) Stocking of nauplii – Wild gravid mother shrimps were collected by shrimp trawlers from the Bay of Bengal. Egg washing and nauplii washing protocols (as per above mentioned ref.) were practiced properly to avoid viral and other pathogenic infection. (4) Temperature: The temperature of LRT water was around 29-30°C. There was no need to use water heater or boiler. Often temperature was found to drop at dawn, when the LRT need to be covered with black polyethylene to avoid any loss. (5). Illumination – In zoeal stage, LRT were always covered with black polyethylene to avoid illumination. This cover was removed for diffused illumination at late M/2 sub-stage after the first water change (when phytoplankton feeding was stopped). This diffused illumination was continued throughout the study period. (6). Water exchange and change of salinity – There was no water exchange or change of salinity in the zoeal stage. First water exchange (about 37.5-40%) at the same salinity was done when conversion into mysis was completed (i.e., in M/1 sub-stage). In late M/3 sub-stage (just before PL starts) a little addition of fresh water was done to lower the salinity to promote metamorphosis. (7). pH and alkalinity of water in the LRT during study period – During the study period, the pH and alkalinity of the water in the LRT were measured at every sub-stage of larva, P/1 and P/5 stages, especially eight hours after each exchange/addition of water. HACH field-kit was used to measure the variables. (8). Feeding – All stage and sub-stages were supplied with both live food and supplementary food. The zoeal stage was supplied with the most common marine phytoplankton Skeletonema costatum as natural live food. (9). Disease and use of chemicals – No infectious disease remarkably affected the tanks under observation during the study period. There was no any U.V.Sterilizer or Ozonator to sterilize the exchanging water. Therefore, the preventive dose of selective antibiotics and protozoacides were used periodically in the LRT (before stocking of nauplii and after each time water exchange) to sterilize the water. EDTA (2Na) was used time to time to improve the water quality. The preventive dose of Traflan was used to prevent fungal infection in the LRT at 24 hours interval from spawning throughout the study period. (10). Sampling considerations – The counting of larvae/PL was always done at night when the larvae were supposed to be well distributed almost equally throughout the LRT. The sampling of all sub-stage/stage was done when at least 75% were metamorphosed into that sub-stage/stage. After P/5, they have got the tendency to settle in the wall of LRT and counting was supposed to give a faulty result. This was the reason to continue the study only up to P/5 age. All sample sizes were 200ml. At least 5-7 samples were taken in each time to reach an average count.

Source of Information: Bangladesh J. Zool. 34(1): 141-146, 2006

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

The above findings indicated that, zoeal stage was the most critical among the larval stages of P. monodon. and most of the natural mortalities occurred in this stage. The zoeal stage continued for 96 hours in average, with 3 sub-stages which individually continued in average for 15 hours (Z/1), 33 hours (Z/2) and 48 hours (Z/3), respectively. The conversion of 1st zoeal sub-stage (Z/1) was comparatively more critical than that of Z/2 to Z/3. Due to this problem, the conversion rate of zoea into mysis was found to be lower than that of mysis into PL. Therefore, it may be suggested that, the practice of commercial shrimp hatchery operation needs to give more emphasis to the water quality management, quality of both natural and supplementary food and also the feeding technique and all other limiting factors (specially during zoeal stage) to overcome the natural problem as found above.

Knowledge Management: Journal