مجله علوم و فنون دریایی
سال دهم شماره 4 (زمستان 1390)

Caspian roach is regarded as a valuable bony fish that has economic importance in southern parts of Caspian Sea. Investigations show that natural reproduction of this species has been declining during recent years. Restocking of this fish is achieved by the way of artificial reproduction. Loss of genetic stock of this species is of great concern. In the current study, in order to study the population structure of roach, 54 individuals were captured from Gomishan and Anzali wetlands (27 individuals from each region) in April 2007. Genomic DNA was extracted using phenol-chloroform method and investigated by 10 microsatellite loci. The genetic diversity of two regions [(Gomishan: average number of alleles, Na= 11.4, average effective number of alleles, Ne= 7.92, observed heterozygosity, Ho= 0.69 and expected heterozygosity, He= 0.85) (Anzali: Na= 10.2, Ne= 7.38, Ho= 0.71 and He= 0.84)] were not statistically different (P>0.05). Analysis of molecular variance showed high genetic diversity (%95) within populations. The Fst value was 0.046, indicating low genetic differentiation among Anzali and Gomishan regions. In this study, 10 of 20 (10 loci × 2 populations) tests showed significant deviation (P≤ 0.005) from Hardy-Weinberg equilibrium due to the heterozygosity deficiency. Results from UPGMA cluster analysis, based on Nei´s genetic distance, showed that the regions are probably separated from each other.

Water and electrolyte balance is vital for aquatic organisms in both hyper and hypo osmotic environments. Kidneys as excretory organs play an important role in osmoregulation and body fluid homeostasis. In this study a total number of 180 Sobayti (Teleost: Sparidentex hasta) were exposed to different salinities to assess changes in the kidney structure and alterations in plasma levels of electrolytes, glucose and cortisol. Salinity challenges were examined for a period of 14 days in four experimental groups: 40ppt as control and 5, 20 and 60 ppt as other experimental treatments. 24 hours after salinity challenge, significant changes were observed in the lumen diameter of the primary proximal tubule at the sections from trunk kidney in both 5 and 20 ppt conditions (P<0.05). Lumen diameter of the second part of the proximal tubule did not differ in any of the experimental salinities (P>0.05).However, lumen diameter of the distal tubule of nephron in the trunk kidney, increased significantly in 60 ppt treatment 48 hours from starting the experiment (P<0.05). The thickness of the epithelium tubule in both trunk and tail parts showed no significant differences during the adaptations (P>0.05). According to the results, histomorphological changes in the different parts of the kidney returned to the basic structure with in 24 to 48hours after exposure to different salinities.

A feeding trial was carried out where, three protein concentrations [45%, 55% and 65%) crude protein (CP)] and three dietary energy concentrations [20, 22and 24 kj g-1 crude energy (CE)] were fed to 540 yellowfin seabreams (Acanthopagrus latus) fingerlings to establish the protein and energy requirement for this species. 9 treatments with triplicate groups of 20 fish each (initial weight 12g) were stocked in 300-L fiberglass tanks and fed twice a day to apparent satiation. After 8 weeks, the survival rate was not dependent on the dietary treatments, but average fish weight gain (AWG), specific growth rate (SGR) and feed efficiency ratio (FER) were significantly affected by dietary protein (P<0.05). Protein retention (PR) were increased by dietary energy level (P<0.05). Feed efficiency ratio, PER and Hepatosomatic Index (HIS) was not affected by dietary protein and energy concentrations (P>0.05). At same protein level, PER, PR increased with the increase in energy levels from 20 to24 Kj g-1. Carcass moisture and ash contents were significantly affected by dietary protein and energy levels (P<0.05) but carcass protein was not significantly affected by dietary protein and dietary energy levels (P>0.05). With increase dietary energy, carcass fat content was increased from 20 to 24 Kj g-1. The results indicate that the optimum dietary protein and energy levels for growth of juvenile yellowfin seabream are 56. 20 – 57. 47g in Kg-1diet and 21.9-24.56Kj in gr diet and 23.15-25.95mgr kg-1, respectively.

The morphological variations and sexual dimorphism of brown trout Salmo trutta morpha fario residual were studied in two rivers, Chesli and Khorma, in western and eastern of Guilan province using 39 morphometric and 13 meristic characteristics. Univariate analysis of variance (One-way ANOVA) revealed significant differences of varying degrees between the means of the two samples for 25 standardized morphometric measurements and six meristic counts, showing relatively high phenotypic variations between the two populations. No significant differences were observed between males and females, indicating that no sexual dimorphism exists in the studied fish. Plotting of discriminant functions, 1 and 2, for morphometric and meristic characteristics revealed completely obvious separation with 100% divergence between the species of the two areas. Only in Chesli River some differences were observed between males and females according to the meristic’ second function, while there were no morphological differences between males and females in Khorma River. On the average, the correctness of assignment of individuals into their original populations based on their morphometric and meristic characteristics was 87.4% and 70.1 %, respectively.

The effect of dietary mannan oligosaccharide (MOS; activeMOS®) on growth, survival, body composition and intestinal microflora in giant sturgeon juvenile (Huso huso) were investigated for 46 days. Basal diet were supplemented with 0 (control), 2 and 4 g/kg MOS in a totally randomized design trial in triplicate groups. The experiment was carried out in 900 L fiberglass tanks. Fifteen juveniles beluga with initially average weight of 46.89 ± 0.57 g were stocked and fed to satiation daily.Data was analysed by regression analysis and pearson correlation test. There were no significant differences in growth and feeding parameters between fish fed control and MOS supplementation diets (P>0.05), but group treated with 4 g/kg MOS showed significant differences in food intake (P<0.05).The highest and the lowest growth performance were observed in 2 and 4 g/kg MOS treatments, respectively. There were no significant differences in survival rate among experimental groups (P>0.05). Fish treated with 2 g/kg MOS showed significant differences in fat content of muscle tissue (P<0.05), but no significance difference in protein, ash and moisture (P>0.05) were recorded. No significant difference was observed in intestinal lactic acid bacteria among the groups (P>0.05). The experiment indicated that the prebiotic mannan oligosaccharide didn’t influence the growth performance in beluga juvenile and it is not appropriate for supplementation in the diet of this cultured species.