JOURNAL OF MARINE SCIENCES AND TECHNOLOGY
Year:2010 | Volume:8 | Issue:3-4|Papers Count:14

The aim of this study was to determine the changes of cortisol and T3 (triiodothyronine) levels in Acanthopagrus latus, a marine euryhaline teleost, in response to a wide range of salinities. The first experiment was carried out following exposure of juvenile yellowfin seabream to 5, 20, 42 and 60% environments. In the second experiment, the fish were assigned to a gradual adaptation to freshwater. Yellowfin seabream was capable of tolerating direct exposure of salinities from 5% to 60% without showing mortalities. This species was also able to tolerate gradual decrease in salinity in the surrounding medium from seawater (42%) to freshwater through a period of 10 days and successfully adapt to freshwater without showing mortality. This is the shortest period reported in a true marine fish for adaptation to freshwater through an acceptable experimental duration. The plasma cortisol level was increased in groups exposed to 5 and 60%. The highest cortisol level was observed in 60% treatment 12 hours after changing in salinity. The cortisol level of the groups adapted to 60% and 5% conditions were resumed to initial levels after 7 days and 24 hours, respectively. Following 24 hours of treatment, the T3 level resumed to the levels similar to the control, after a little increase. There was no difference in cortisol and T3 levels among control and experimental groups during gradual adaptation to freshwater.

The purpose of this study was effect of different brine concentrations (10%, 15% and 20% NaCl) with two ratios brine to fish (1:1 and 1:1.6), dry salting and storage on salting products yield and biochemical changes of silver carp fillets. Followed factors were studied in dry salting samples and weight was determined in total of salting samples. The results indicated that the different brine concentration significantly affected the weight changes of the fillets. The weight gain of the fillets increased with decreasing brine concentration, which highest and lowest weight was found in 10% and 20% (1:1) respectively. There was an effect of salting different methods on yield (P<0.05) that Maximum and minimum weight was found in brine salting and storage respectively. Moisture and salt content decreased and increased respectively during processing and increasing brine salting (P<0.05). During the increasing of salt content silver carp fillet have significant effect in decreased protein content and increased fat and pH during brine salting, dry salting and storage.

Digestive enzymes have the pivotal role in the nutrient uptake and growth of fishes. However, information about the behavior of digestive enzymes and their restoring potential during different deprivation and refeeding periods is scarce. In this study we evaluated whether rainbow trout with an average body weight of 44.01 g±0.19 S.E. could regulate and rehabilitate its digestive capacity after different feed deprivation periods. The study lasted for eight weeks. Four treatments with three replicates including a control group without food deprivation and treatment 1, 2 and 3 with 1, 2 and 3 week(s) of food deprivation, respectively, were set up. Then, fish were fed ad lib for five weeks from the onset of week four up to the end of week eight, twice daily under photoperiod of 15L: 9D and temperature of 17.4±0.1oC. Specific enzyme activities of trypsin, chymotrypsin and lipase were measured on days 21 (before commencement of feeding), 33, 43 and 55 (the end of the experiment). At the end of deprivation period the control group had significantly higher (p<0.05) trypsin activity (95.4±12.2) compared to treatments 1 (78.1±5.1), 2 (75.2±10.1) and 3 (85.4±9.3). Starved treatments showed no chymotrypsin activity at the end of starvation period as compared to the control group which showed the enzyme activity of 44.77±9.4. Lipase activity of the control group (37.7±2.3) was significantly higher (p<0.05) than those of treatments 1 (23.0±2.4), 2 (22.1±2.2) and 3 (27.3±5.0) on day 21. However, upon elongation of the feeding period up to day 55, the enzyme activity levels were restored to the level of control group (p>0.05). The results clearly indicated that food intake is one of the main mediatory factors to regulate digestive enzyme activities and fish can restore its digestive capacity following different deprivation periods.

17-methyl testosterone is an androgenic hormone and is involved in the sexual cycle and is used in increasing growth and masculinization. In this study, effects of different doses of hormones (300, 400 and 1000 mg/kg. diet) with a control treatment (0 mg/kg. diet) on secondary sex characteristics of male fish (Gonopodium index and color) and female (color measurement), the evolution of fish Ovaries and larvae production of guppy (Poecilia reticulate) were studied. Gonopodium index values in males did not show significant differences. The results also indicate increased red pigment in the male and female fish. While increasing the hormone dose, sperm sac was formed in the ovaries and follicles reduced and as a result of it, larvae production was reduced. When the dose was highest, after about 5 weeks larval production was failed. Our results indicate a strong relationship between physiological characteristics of fish and color and secondary sex characteristics.

The effect of dietary mannanoligosaccharide (MOS, activeMOS®) on growth, survival, body composition and salinity stress resistance in Kutum (Rutilus frisii kutum) fry stage was investigated for 8 week. Fish with initial average weight of 741.8±37.4 mg were randomly distributed into fiberglass tanks (300 fish per tank). Experimental diet were supplemented with 0 (control), 1.5, 3 and 4.5 g MOS per kg commercial kutum feed in a totally randomized design trial in triplicate groups. At the end of experiment the kutum fry were exposed to salinity stress. There were no significantly differences in growth and feeding parameters between fish fed control and MOS supplementation diets. The highest and the lowest growth performace were observed in 1.5 and 4.5 g/kg MOS treatment, respectively. The group tested with 1.5 g/kg MOS had significantly higher survival rate and intestinal lactic acid bacterial countnt (P<0.05). There were no significant differences in survival index after 48 hours salinity stress. And body composition was observed (P>0.05). The results indicated that 1.5 g/kg MOS could improve growth, survival and stress tolerance in kutum fry.

This trial was carried out for a period of 60 days to investigate the effect of temperature levels (24, 28 and 32oC) on growth, survival, feed intake, blood parameters and body composition in Kutum (Rutilus frisii kutum) fingerlings (initial mean weight 0.2±0.03 g). The mean final weight of kutum fingerlings was 1.68±0.06 g. The highest daily growth rate (DGR), weight gain (WG), specific growth rate (SGR) and percentage of body weight gain (%BWG) were highest at 24oC, and the lowest of these parameters were observed at 32oC. In case of these parameters, no significant difference (P>0.05) was observed between 24oC and 28oC while this temperature had significant difference (P<0.05) as compared to 32oC. The fingerlings reared at 32oC, showed the slower growth rate, lower feed intake, and higher FCR than other treatments. Mortality did not indicate significant difference (P>0.05) among different temperatures. The optimum food conversion ratio (FCR) of kutum fingerlings was obtained at 24oC. Condition factor (CF) and mortality rate, blood parameters, and body composition did not show significant difference among treatments (P>0.05). Glucose, cholesterol, total protein, Calcium, Magnesium, Sodium and Potassium had no significant variation among different treatments at the end of the experimental period (P>0.05). Hematocrit affected significantly by temperature (P<0.01). Results suggested that fingerlings of Kutum, reared excellently at temperature water among 24oC to 32oC.

The present research attempts to study the variations of the inflow over a bed slope break that simulates the delta formed in dam reservoirs and rivers mouths. The inflow and density current variations were studied by a physical model, which was developed for the purpose of this study, and a bed break with different slopes. The results showed variations up to 1.65 of the flow velocity along with variations up to 3.5 of the inflow thickness. Water entrainment showed a great sensitivity to the variations of reservoir elevations along to those of Richardson Number for which a power equation is presented.

The aim of this study is to predict attenuation coefficient of sound waves in the Persian Gulf whose experimental values are not available. In this study COHERENS which is a three-dimensional hydrodynamic model is employed in order to predict temperature, salinity and pressure in different layers. Also by adding the theoretical equation of attenuation coefficient into this model, relationship between salinity, temperature with attenuation coefficient of sound is calculated. Results of the model shown that the minimum monthly average values of attenuation coefficient in the bottom layer is occurs in July and August in the northern coasts of the strait of Hormuz as well as west northern part of the Persian Gulf near the Arvand river mouth. Also maximum monthly average values occur in February on the surface in southern parts of the Persian Gulf. Outputs of the model showed that monthly average of attenuation coefficient in bottom layer is greater than surface, whereas the attenuation coefficient on the bottom is smaller than the surface only in November, December, January and February.

Biological characteristics of Madagascar meager, in Choebde and Bahrekan areas, in the east coast of Khuzestan were investigated. During one year study from November 2008 to October 2009 total of 143 fish specimens were analyzed (74 males and 69 females). The Gonadosomatic Index (GSI) for the male and female were calculated as 0.66±1.29 and 2.83±2.42 respectively, with the highest value in August. The length-weight relationship were calculated as Y=0.042L^2.70 (n=74, R2=0.86) for males, Y=0.061L^2.61 (n=69, R2 =0.85) for females and Y=0.059 L^2.62 (n=143, R2=0.86) for total fish. The growth indices for total studied fishes were found to be L=161.61 (cm), K=0.57 (year-1) and to=-0.17. According to biological characteristics and compared to American fisheries society (AFS) indices, Argyrosomus hololepidotus is classified as highly vulnerable fish.