Journal of Fisheries
Year:2010 | Volume:63 | Issue:3|Papers Count:7

In this study, the osmolality of haemolymph and haemolymph ionic level changes (Na+, Mg+2, K+, Ca+2, Cl-) in white shrimp (Litopenaeus vannamei) were investigated under different salinities, i.e. 15, 25, 35 and 45 g L-1 at  30 ˚C using a completely random design with three replicates. Specimens experienced natural light condition and pH 8-8.5 for 35 days. Then, the osmolality of haemolymph and ionic concentration in haemolymph of shrimp were measured. Although the level of sodium, magnesium, potassium and chloride increased significantly with the increase of salinity, no significant differences happened in calcium leves of haemolymph. In all treatments, levels of calcium in haemolymph were higher than that of the ambient culture water, however, level of magnesium in haemolymph, in all treatments, were very lower than that of in the ambient water. Results showed that vannamei shrimp have strong ability to regulate haemolymph ionic concentrations.

An experiment was conducted to determine the efficiency of two kinds of substrata (Polypropylene and Populus shaving), as biofilter media on removal of ammonia-N and fish growth in a recirculating aquaculture system for a 6-week period. Rates of survival in treatment with Populus shaving was significantly (P<0.05) more than Polypropylene treatment, these rates were 96.67 ± 3.33 and 92.31 ± 3.50% (mean ± SD), respectively. The mean (± SD) initial individual weight of fish was 3.4 ± 0.20 g and the fish attained 7.32 ± 0.17, and 5.11 ± 0.11 g in treatments with populus shaving and polypropylene, respectively at the end of experimental period. Concentration of total nitrogen, total ammonia-n and nitrate were significantly different (P<0.05) between treatments at the end of the experiment. Concentration of total ammonia-n reached to 0.20 ± 0.04 and 0.44 ± 0.01 mg L-1 in populus shaving and propylene treatments, respectively. Concentration of total nitrogen were 1.70 ± 0.14 and 0.84 ± 0.20 mg L-1 in treatments with populus shaving and propylene, respectively, at the end of experiment It was concluded that populus shaving, can be used as a biofilter medium  in a recirculating fish culture system.

Water treatment in recirculation aquaculture system is one of the main methods in water quality management. Invention of various treatment methods with maximum capability and low primitive coast is significant concern for aquaculturists. The negative surface of zeolites capable them for adsorbing cations, hence by modifying zeolite's surface structure, they will be able absorb anions. Basic anion exchange resins are the main ion exchanger that have high anion adsorption capacity. At the present study natural Iranian zeolite was modified by cationic surfactant at various conditions (temperature and pH), then anionic adsorption capacity was investigated. Experiment was done at three times, under various temperature (10, 15 and 20° C) and pH (6, 6.5, 7, 7.5 and 8). Results showed that environmental conditions influenced the anionic sorption. Increase temperature resulted in similar trend in the anion adsorption by adsobant materials, however Amberlite had a higher adsorption rate. Nitrite absorption by amberlite initially decreased and then increased but zeolite showed an inverse of that Ambelite. Nitrate adsorption by the two adsorbents was regular and increasing. An irregular trend was observed in nitrite adsorption with change of pH. Results showed that modificationof zeolite by cationic surfactantcan be used as a new adsorbant in recirculation aquaculture systems because of thelow cast of its primary materials.

Determination of spawning period and peak time of it has a crucial role in stock management and restocking of fish species. In the present study, the ovarian development and spawning of common carp in south-east of Caspian Sea were examined through histological studies. At the beginning of the study, samples were obtained through seining that was performed through commercial fishery organizations (the Golestan province) from October to March. Later, samples obtained through fishing by research organizations. Samples were taken randomly from the beach seine nets. The samples were considered from different aspects: fecundity, oocyte diameter, biometry, identification of different maturation stages, and gonado-samatic indices (GSI). Hematoxilin-Eosin method was used for staining of oocytes. Identification of maturation stages was done based on six-stage key. In the mean, absolute fecundity was 143302.8. GSI elevated until early January and then decreased. GSI increased sharply again until May. In June, a sudden decrease in changes was seen. The results from gonadosamatic index and histological studies showed common carp gonad has a continuous spawning period in the Caspian Sea and the spawning occurred initially over at least 8 months.

Grass carp is grown along other cyprinids in earthen ponds. A part of common carp pellet may be consumed by grass carp in a polyculture system. The present study aimed to assess the effect of pellet on growth parameters, i.e. mortality and morphology of gastro-intestinal tract of grass carp. The experiment was conducted by the use of grass carp with an initial body weight of 1.17 ± 0.036 g (mean±SD). Two experimental diets were used: the pellet and grass diets. Fish were randomly allocated to six tanks and each tank received 40 fish. Each diet treatment had three replicates. Fish were fed two times per day (mooring and afternoon) at satiation level. Feeding by pellet improved some of the growth parameters such as final weight، growth and specific growth rate (P < 0.05) compared with the grass diet. There was a reduction in mortality rate of the specimens fed the pellet diet. The fish fed on the grass diet had a ratio of the intestine weight to the fish weight higher than that of the fish fed on the pellet diet (P < 0.05). Pellet diet increased in body fat content of grass carp (P < 0.05). In conclusion, the grass carp was able to use pellet diet although the diet caused a change in gastro- intestinal tract and body composition compared with the grass diet.

Water inlet rupture, flood water, blocked net monk in autumn or mortality and carry away crops in midnight when the farm keeper asleep are the main probable reasons for variations of water level in ponds and water inlet channel. Water level controller was constructed for accurate monitoring and calling in critical situations. This unit composed of sensors, mother board, thermometer circuit, power source, audible and flash alarm. CMOS IC with six Schmiths trigger gate was installed in mother board. A pipe with one meter in length and 2 inch in diameter was used for sensing water levels. A new IC which could measure water temperature from -15 up to +50°C was employed. Parallel nickel-cadmium batteries were used for reliability reasons with the possibility of electrical power charging. Two solar cell boards charging prepared for areas which don’t access to electrical power. Constructed system tested in a tank. After water level reached to the critical lower or higher points which were operated before, alarm and red flashing warning light were working properly. Possible up and down vertical movement was prepared for operating the height pipe sensor according to the pond and channel wall elevations.

Modifications in fat and fatty acid composition during prolonged storage of canned common kilka (Clupeonella cultriventris) were studied. In this study common kilka was processed under traditional Mediterranean method and then stored for up to 3 years. Qualitative characteristics including total fat, fatty acids profile, free fatty acids, thiobarbituric acid, fluorescence compound of filling media and aquatic phase of lipid extract in fish (row canned and stored canned) were determined and compared with each other. Results showed that canning led to a decrease in total fat, although during 3 years storage, total fat did not change significantly. During the long term storage, amounts of free fatty acids, fluorescence and secondary lipid oxidation compounds were increased significantly. After canning, linoleic acid of tissues increased significantly as result of the interaction between tissue lipid and filling media. EPA and DHA of canned fish tissue decreased. Some of these fatty acids with other specific fatty acids were found in the sunflower oil that was used for coating. During prolonged storage, the n-3/n-6 ratio of tissue’s fatty acids decreased. At the same time, this ratio, in filling media, increased. Results of this investigation showed that, with increase of storage time, interaction between tissue fatty acids and filling media increases.