فصلنامه شیلات
سال شصت و چهارم شماره 4 (زمستان 1390)

The present study aimed to investigate the effect of lowering dietary protein level at different feeding times on nitrogenous wastes production of rainbow trout in a semi-recirculating system. Accordingly, two diets one with higher protein level (41.5%), diet A and the other one with lower protein level (36.5%), diet B were used at two different feeding times, to comprise 4 distinct treatments. Treatment one received diet A at both morning and evening feeding times. Treatment two was fed with diet A in the morning and diet B in the evening, while third treatment was fed exactly opposite as compared with treatment two. Treatment four received diet B at both morning and evening feeding times. The average total nitrogen and total ammonia, nitrite and nitrate were used as indices of nitrogenous wastes production throughout the experiment. Decreased dietary protein levels from treatment one to treatment four did not pose desirable effects on growth, FCR and survival rate, however, a positive correlation was observed between nitrogen intake (protein) and nitrogenous wastes production (P<0.05; r=0.81). Decreased dietary protein level in one meal (treatments two and three) caused no significant difference to growth and FCR compared to treatment one, however third treatment resulted in lower nitrogenous wastes production (P<0.05).

Some biological aspects of Greater lizardfish (Saurida tumbil) caught on the Iranian shore of the Persian Gulf (Bushehr Province) were studied from February 2007 to February 2008, by regular monthly collections to gain a deeper knowledge about this commercial species. A total of 691 specimens, including 39 immature, 114 males and 538 females were collected. The mean of the sex ratio was 1:5 (M:F) which was inverse in juvenile where males were the dominant group. For age determination, scales in all specimens and for comparison, otoliths in some, were used. The total length of fish ranged from 25.5 to 53.5 cm in males and the total weight of fishes ranged from 116 to 1125 g. The curvilinear relationship between the total length and total weight was w=0.0093 L2.9369 for males. Histological studies and monthly distribution of GSI, showed that the GSI values have two peaks; the first and highest in May and the second and smallest in October. The minimum GSI was determined in December. It was found that male Saurida tumbil reach the first sexual maturity at 25.5 cm. Sections with 5-7 µm thick were stained with Hematoxyline-eosin for microscopic examinations. In the histological study, spermatogonial proliferation stage, spermatogenesis, prespermiation and degeneration stages were observed.

This study was conducted to determine the feeding habits of Mudskipper Scartelaos tenuis. One hundred and eighty one specimens were collected in the northern part of Persian Gulf in Bushehr province during spring 2007 to winter 2008. Specimens caught by hand and dip net. Specimens fixed in 10% formalin and transferred to laboratory. Stomach contents were analyzed; possibility and frequency of prey were calculated with standard methods. Results showed that in S.tenuis copepods with IP index of 69.18% was the dominant and specific food item. There was no seasonal variation in food items. Stomach emptiness was the highest (32%) in winter and lowest (10%) in autumn. The RLG index was 1.4 that indicated the fish was omnivorous. Totally Stomach emptiness index was 20% that suggested the fish being a voracious feeder.

This study was carried out within 7 months in Dikjeh area, Golestan province, Iran. During that time the relationship between water salinity and EC with hematocrite, blood serum ionic parameters, growth, survival and stress indices in common carp (Cyprinus carpio) were investigated. Hematocrite as stress index was measured by hemocitometry standard method using microhematocrite reader. Fish biology assay characteristics such as length, weight, condition factor and growth rate in every month were determined. Common carp with average weight of 45 g was abandoned and after 7 months average gaining weight reached to 705 g. The range of salinity (0.3-2.7 ppt), EC (843-5230 µm/cm2), Na+ (43.59-408.7 mMol/l), K+ (0.90-9.21 mMol/l), Ca2+ (2.69-18.29 mg/dl) and Mg2+ (0.80-10.88 mg/dl) were measured. According to the Pierson, water EC with length, weight and Mg2+ of blood serum and biomass of fish had positive correlation but with condition factor and Ca2+ of blood serum had negative correlation. Water salinity with length, weight, biomass of fish and Mg2+ of blood serum and with K+ of blood serum showed positive correlation. But survival and blood hematocrite had not significant correlation with this range of water salinity and EC. As a result, common carp in this range of water salinity (0.3-2.7 g/l) and EC (843-5230 µm/cm2) without stress has a suitable growth and because of isoosmotical status with environment and less energy expenditure, has a higher growth.

The concentration of cadmium in the muscle of Periophthalmus waltoni in Persian Gulf (Bandar Khamir, Dargahan and Golshahr) and the effects of two seasons (winter and summer), gender (male and female) on the accumulation rate of cadmium in these fishes was determined. A total of 180 samples of Periophthalmus waltoni (in each station and each season separately 30) in three above regions during both seasons of winter and summer were collected. Then the samples were transferred to the lab and after biometry (total length and total weight measurements) of samples, 2gr of muscle tissue excluding dermis was separated. after drying in the freeze-dryer for 8 hours. powdering the sample, 0.5 gr of the dried sample tissue for chemical digestion along with increasing acid nitric 65% and hydrogen peroxide 30% was put in microwave. concentration rate of cadmium was measured by atomic absorption apparatus. The results indicated that the concentration of cadmium in the muscle tissue of P. waltoni, there is significant difference in the studied regions and seasons (winter and summer) (P< 0.05). In both seasons Bandar Khamir (summer: 0.214±0.008 and winter: 0.115 ±0.010) has the highest concentrations of cadmium comparing to Dargahan (summer: 0.201±0.02 and winter: 0.102 ±0.08) and Golshahr (summer: 0.150 ±0.09 and winter: 0.011 ±0.04). The concentration of cadmium between male and females of P. waltoni in the studied regions indicate no significant difference. Considering the results of this paper, it may be concluded that the pollutions due to oil, industrial and civil activities in different regions in Persian Gulf (Bandar Khamir, Dargahan and Golshahr) during different seasons influenced the accumulation trend of cadmium in P. waltoni.

This study was carried out to evaluate the effect of commercial live bakery’s’ yeast(Saccharomyces cerevisiae), (marketed as Amax), on growth and survival of Persian sturgeon(Acipenser persicus) larvae (74.9 ± 9.7mg) during 30 days. Sturgeon larvae were fed on Daphnia magna enriched at three suspensions of yeast, Amax, (0, 50, 100, and 150 mg yeast per litter). The feeding level was 30 percent of total biomass per day. The daily ration was divided into five feeding portions and fed by hand. Growth parameters were influenced by yeast-enriched daphnia (P<0.05). Feeding on enriched daphnia caused a higher specific growth rate and a better feed conversion ratio than those received control daphnia (no enrichment; P<0.05). Feed efficiency was increased significantly (P<0.05) at experimental treatments in comparison to the control diet. The highest growth was observed in the treatment with 150 mg yeast. There was also a positive relationship between enrichment levels and growth related parameters. However, no significant difference observed in the condition factor among the treatments (P>0.05). Survival rate of the larvae improved by using Amax compared to control diet (p0.05). Fish fed on yeast-enriched daphnia showed a higher resistance to unwanted environmental factors (P>0.05). In conclusion, the current experiment indicated that the supplementation of daphnia with Saccharomyces cerevisiae can increase the growth performance and feed efficiency and also up-grade the stress tolerance in Acipenser persicus larvae when facing with unfavorable environmental conditions.

This study was conducted to assess water quality level of Zarin Gol stream on macrobenthic invertebrates. Macrobenthic fauna were sampled from 9 selected sampling stations along the stream with an average distance of 22 km by using a Surber sampler every 45 days during the year. Sampling was replicated 9 times in each sampling station. Collected samples were fixed with 4% formalin, isolated, and then identified. The number of total abundance of macrobenthic fauna were counted to 2749.021 ± 1301.8 (ind/m2) belonging to 15 orders and 81 groups (families and genus). The minimum and maximum of total abundance (ind/m2) was at station 1 (370.63 ± 231.1) and at station 5 (215. 73 ± 101.75), respectively. The main orders of macro benthic invertebrate communities in Zaringol stream included Diptera, Ephemeroptera, Trichoptera, Plecoptera, Oligocheta, Odonata and Amphipoda. Population structure of macro benthic invertebrates were analyzed by biotic Indices and the results showed significant differences in EPT and EPT/CHIR indices at different sampling stations (p<0.05). Hilsenhoff and Shannon diversity indices indicated no significant differences (p>0.05) along the stream. Evaluation of indicators revealed less water quality at stations 2 and 5 where located at the lowermost of fish farms. This reduction might be implicated to the effluents of water damps from fish farms running into the stream as diversity and total abundance (%) of succible macro-invertebrates decreased and that of resistant macrofauna increased due to water pollution. Hence, from the obtained results, this can be concluded that the use of benthic macro-invertebrates as bioindicator for the assessment of water quality of the stream is desirable.