Iranian Journal of Fisheries Sciences
Volume:6 Issue: 1, Jun 2006

The virucidal effect of pH and salinity on Penaeus monodon baculovirus (MBV) was investigated by water borne inoculated methods exposing PL12 Penaeus semisulcatus for 10 hours and observing for 10 days at temperature 28- 30°C. For this purpose, one thousand virus free PL12 of P. semisulcatus were divided into five groups and each group placed in a 10 L plastic basin containing chlorine-treated sea water at 35ppt. The salinity of basins water after 12 hours changed to 5, 10, 20, 30 and 40ppt using synthetic sea salt. To study the effect of pH, solution with various pH of 3, 5, 7, 8, 9 and 12 were prepared using IN NaOH and IN HCL to Na2HPO4 solution. For transmission of MBV, an aliquot of approximately 10 frozen infected larvae were used for each experiment by water born inoculated method. Ten hours after inoculation, the shrimp were removed from jar and introduced into another jar with the same salinity or pH. During 10 days experiment, the rate of infection (ROI), severity of infection (SOI) and accumulative mortality were varied among the MBV-infected. Penaeus mondon baculovirus was able to infect Penaeus semisulcatus at salinity ranging from 5-40ppt whereas at pH 3 and 12, MBV was completely inactivated MBV was not able to infect larvae at pH 5, 7, 8 and 9.

The optimum dose of UV irradiation to produce gynogenesis rainbow trout, Oncorhynchus mykiss with emphasis of Hertwing effect and photoreactivation (PR) was investigated. For this purpose, the sperm of rainbow trout were inadiated with UV at 2010±200 µw.cm-2 intensity in different alternatives of 0, 1, 3, 5, 8, 10, 15, 20, 25, 35 and 45 minutes and allowed to fertilize normal ova; the fertilization, eyed and hatching rate were calculated to assess the performance. Using the irradiated sperm decreased the fertilization, eyed as well as hatching rates and the so-called "Hertwig effect" was observed, with the time-dependent decrease in hatching rate at 0+to 10 min of irradiation, but a better hatching rate at greater time of irradiation was observed. The highest hatching rate was observed in 20 min of UV irradiation; after that the survival rate decreased rapidly. Interestingly, irradiation even up to 45 min could not eradicate sperm fertility and a hatching rate above zero was observed at this treatment. For PR studies the semen was irradiated with UV for 5, 30 and 120 seconds and untreated semen (Os) was used as control. Irradiated semen and/or fertilized eggs by treated semen were exposed to visible light (60 W) at a distance of 30 cm for 10 min; the eyed and hatching rates were measured. The results showed that UV irradiation in as low as 5s could cause deleterious effect on semen chromatin and decrease the eyed and hatching rates (p<0.05). Illumination of semen andor eggs with visible light resulted in PR in rainbow trout when sperm was irradiated by UV at 120s. We could conclude that the best UV irradiation time for production of gynogenesis rainbow trout was 20 min and UV irradiation, fertilization and egg hardening must be done far from visible light to eliminate the PR mechanism.

A red-tailed catfish (Phractocephalus hemioliopterus) referred to Aquatic Animal Health Department, Faculty of Veterinary Medicine, University of Tehran for showing lethargy, bottom sitting, extension of abdomen and severe abdominal injuries. Its abdomen was swollen and the bulk of the foreign bodies were easily palpated. The heaviness of foreign bodies had made swimming and buoyancy difficult for fish. Several radiographic images were taken after anaesthetizing the catfish with 10% carvacrol, 2 drops in 1 liter of water. Radiographs revealed some stones with their size, number and location. Stones were removed non-surgically through the large oral cavity using suitable forceps. Totally 16 stones and 2 shells were removed from the stomach of the fish. The catfish was then returned to the water where normal swimming and buoyancy was restored.

The osmoregulatory system was studied in wild adult and reared juvenile Persian sturgeon, Acipenser persicus. The mean osmolarity in blood serum of specimens from the Caspian Sea, estuary, the Kouraneski pools and the rearing tanks were 305.3±14.3, 308.7±25.8, 265.0±19.1 and 259.3±8.8 mosmol/L, respectively; the mean concentrations of Na+ were 151.2±6.3, 152.2±8.4, 142.5±5.9 and 131.4±4.1 meq/L whereas mean concentrations of K+ were 2.7±0.9, 3.6±0.9, 3.1±0.5 and 2.6±0.5meq/L, respectively. The concentrations for Mg++ ion in fish of the same four origins were 1.5±0.2; 1.5±0.3, 0.8±0.2 and 0.7±0.2 meq/L, and those of Ca++ were 2.31±0.51, 2.61±0.51, 1.85±0.58 and 1.46±0.43, respectively. The Pearson's correlation coefficient and regression equation indicated that Mg++(r =0.38) and Na+ (r=0.41) were effective ions for determination of blood serum osmotic pressure in A. persicus in brackish water and freshwater. This study also showed that blood serum osmotic pressure was independent of sex.

Chemiluminescent response of grass carp (Ctenopharyngodon idella) was assessed to determine the effect of various concentrations of diazinon on the phagocytosis of grass carp in order to evaluate the fish immunity after exposure to this toxic chemical. One hundred and twenty specimens with individual weight of 850±155g were exposed to various concentrations of diazinon at 1, 2 and 4mg/L provided as a bath for 12 hours at 20±2°C in Institute of the Caspian Sea Ecology, Sari in 2003. Maximal values of spontaneous chemiluminescent responses (SCL) were found in all experimental fish only on days 1 and 7 post-exposing to the toxicant compared to control one (p0.05). Generally, the level of chemiluminescent response activated by zymosan (CRAZ) at all concentrations of toxicant were significantly higher than control group after 1, 7, 15, 30 and 45 days post-exposure to the toxicant (p<0.05).

A completely randomized experimental design was conducted to estimate ammonia excretion rate by red tilapia (Oreochromis sp.) during different stages of its growth in recirculating water system units typically designed to meet the experiment purposes. Eight weight groups each containing 75individuals of 20, 30, 40, 60, 80, 120, 180 and 200g average weight were considered as treatments in duplicates. The rate of ammonia excretion by each fish group was measured during a 24-hr period. The data was extended to estimate total ammonia excreted by a group of red tilapia during a 115-day culture period (20-200g). The mean daily ammonia excretion rate was significantly different between treatments (p<0.05). These rates were 34.06±1.23, 32.56±3.28, 27.06±0.87, 17.46±2.19, 12.54±1.30, 12.48±1.41, 7.87±1.82 and 5.83±0.19 mg kg fish-1 h-1 for 20, 30, 40, 60, 80, 120, 180 and 200 g fed fish, respectively. It was estimated that on average 39.4% of input feed nitrogen excreted as ammonia-N during the culture period. Results of this study well addressed the regime of ammonia production in different stage of red tilapia growth in a recirculating water system.

Impact of Atlantic salmon (Salmo salar) cage culture in Mjoifjordur, Eastern Iceland on the chemistry of the sediment was investigated. Sediment samples were collected using a Shipek grab in December 2003. A core sub-sample was taken from each grab for analyzing total organic matter, total organic carbon, total nitrogen and phosphorus in different depths from three stations at various distances from the cage. These parameters were analyzed in the top layer of additional four stations. The results showed significant increase in all analyzed parameters in station 1, at 5m from the cage (p0.05), indicating localized impact of cage farming to the vicinity of cage. The analyzed parameters in various depth did not show significant differences (p>0.05). The value of analyzed parameters in the perimeter of the cage and their differences with reference stations showed small magnitude and localized impact on the chemistry of sediment. It might be due to deep water and moderate velocity of water current in this fjord. The magnitude of impact may differ during the summer season when biomass and feeding rate would be at the maximum level.