S. A. Uddin*
Institute of Marine Sciences and Fisheries, University of Chittagong, Chittagong-4331, Bangladesh
M. M. Rahman
Institute of Marine Sciences and Fisheries, University of Chittagong, Chittagong-4331, Bangladesh
Penaeus monodon shrimp, Moulting, Re-maturation, Spawning, Eyestalk-ablation
A reputed shrimp hatchery, Cox’s Bazar, Bangladesh
Animal Health and Management
This study was carried out from April 2014 to July 2014 in a reputed shrimp hatchery, Cox’s Bazar, Bangladesh, where adequate research facilities for the study of hatchery operation and management were readily available. Adult broodstocks (60 female and 20 male) were collected from the south and western part of the Bay of Bengal, e.g. elephant point, bottom of the St. Martin’s Island and Kohinur point using a fishing trawler namely, Fisher 2. Animals, that are in good condition (i.e. no sign of stress), and minimum of 165mm length, and weight about 50 g (for male), and of 200 mm total length, weight about 65 g (for female), were chosen. Usually, five individuals of broodstocks were transported in a broodstock carrying polythene bag filled with water (1/3) and oxygen (2/3), were used to transport the animals from ships to the hatchery. Acclimation and water management The broodstocks were quarantined with 500 ppm formalin for 2 minutes (dip bath) and acclimated to ambient water conditions at the hatchery in a 15 ton cemented broodstock holding tank. After acclimatization (1/2 days later), the animals were then transferred to the maturation tanks (12 ton cemented) at the density of 6-7 animals /square meter, at 1:3 ratio of male to female. Two hours before, 10 pm EDTA (Ethylene diamine tetra acetic acid, a chelating reagent) and 0.1 ppm treflan (fungicide) were applied prior to transferring the animals. Oceanic quality seawater was provided at all times as defined as salinity 26 to 32 ppt, temperature 28 to 320 C and pH 7.8 to 8.5. Filtered (cartridge filter, 0.5µ) and disinfected (UV treated) seawater was always used. The tank was covered with a black corrugated plastic, and sufficient aeration was provided. The water level in the maturation tanks was kept at the level at 60 cm with a constant flow of about 10 liters/minute which provides 200% exchange/day. The water in the maturation spawning and hatching tank was kept with the minimum disturbance. Feeding management About 12% of the estimated shrimp biomass was fed to the shrimp and the feeding distributed proportionately with various feeds like squid, clams. The shrimps were fed fresh diet in twice daily at early morning at 6.00 am and late evening at 7.00 pm. The remaining feed and fecal materials were siphoned out in the morning, and the lost water was replaced with fresh seawater. Fresh squids and clams were brought once a week. Skin and all internal organs were removed and rinsed well to eliminate all traces of ink and cutting into small pieces about 1-2 cm and stored in a deep freezer for the whole week. According to the requirements of individual tanks, feeds were weighed out. All tanks were equipped with aeration. For controlling of photoperiod, a balanced light/dark phase was maintained by artificial lighting in the maturation room. The fluorescent lights covered with dark blue acrylic sheets to provide very subdued light similar to the natural habitat of the adult shrimp. For prophylactic treatment at first the water volume of the tanks was lowered up to 3 tons in the reservoir. Formalin was applied at a rate of 50 ppm (two-hour static treatment with no water flow) and the tank flushed out after the treatment. Induced maturation by unilateral eyestalk ablation Before ablation, the males and females were segregated in two separate tanks containing 100 liters of seawater. A single female from the tank was removed and hold it in one hand with the head facing away from the body and observed the both eyes for any damage. At first the damaged eye was ablated, otherwise left or right one was ablated. Ablation was carried out unilaterally with a heated surgical forceps. Povidone iodine (1%) was swabbed on the cutting side (Fig. 3) to prevent any fungal infection. After ablation, females were placed in indoor tanks containing 10 ppmoxytetracycline solution (FDA approved drug) for half an hour and then released to the maturation tank. Selection of potential spawners The gradation of maturation was examined externally by shining the light on the side of the abdomen with a waterproof hand light, particularly in the area behind the cephalothorax. Potential spawners were those, which showed thickening of the ovarian wall all along the length of the abdomen. The selected spawners with ripe ovaries was removed and dipped for about 2 minutes in 500-ppm formalin. After formalin bath, the female was rinsed with filtered, disinfected seawater and then placed into the 400-liter spawning tank. The moulting, maturation and spawning of each female were checked daily. For this purpose, the females were marked by pasting various colored plastic labels onto the carapace and making coded cuts in one or more uropods. Spawning and Hatching After spawning, the spent females were removed from the tanks by a scoop net and returned to the maturation tank. The tank water (spawning) was drained, and the eggs were passed through a 350 µ hand net that retains feces and they were collected on a 150 µ hand net in a bucket. Before transferring the eggs to the hatching tanks, they were washed thoroughly with running seawater at least for 10 minutes. Preparation of hatching tanks and stocking After counting, the eggs in the harvesting bucket were transferred to hatching tanks containing one ton of water. The eggs were spread on the tank water gently and evenly. The aeration in the tank was adjusted to a minimum level. Before transferring the eggs to the hatching tanks, they were again treated with 10ppm EDTA and 0.05 ppm treflan and 2.0 ppm Oxytetracycline. Hatching: After spawning the nauplii were hatched out in about 12-15 hours under normal circumstances (temperature 28 -32 and salinity 29 -34 ppt).The nauplius reached the 6th sub stage N1-N6 within 30-36 hours. Microsoft Excel and one–way ANOVA in BioStat v5, Analyst Soft Inc.-statistical analysis program for Windows, carried out statistical analysis i.e mean, standard deviation, standard error and p-value.
J. Bangladesh Agril. Univ. 13(2): 315–322, 2015 ISSN 1810-3030
Journal