---

Viviparity is an advanced reproducing process observed in certain bony fishes. Fish oocyte is protected by different coverings, the immediate one over oolemma being a non-cellular membrane known as Zona Radiata (ZR). ZR has shown variations in thickness, configuration and probably function at different fish oocyte and oocyte growth stages. In the present research work the ultrastructure of zona radiata around oocytes of guppy (Poecilia reticulata) has been studied by light and scanning electron microscopy methods concerning different oocyte growth stages. ZR was not observed at stages I and II. At stage III ZR was observed as a thin layer around the oocyte. It increased in thickness and complexity at stage IV (vitellogenesis) but showed different appearance and declined in thickness during the following stage. External surface characteristics, features of pore canals and probable function of ZR during oocyte development were also investigated.

---

In the research project performed, the effects of different levels of hydro-alcoholic extract Vitex agnus-castus were investigated as nutritional supplement on growth parameters of Danio rerio for 4 months. Since the beginning of the feeding phase up to the age of 4 months (average weight: 2.1±0.1g, length: 5.2±0.3 cm), larvae were fed with expe-rimental diets. Fish treated with diets containing plant extracts had higher growth and survival rate than the control gr-oup (p<0.05). Differences in the level of the extract had no significant effect on the survival rate (p<0.05). The results revealed that the diet containing 15 gr of the extract resulted in the best FCR significantly (p<0.05). By increasing the extract in the diet during the experiment, SGR increased. The highest and the lowest %BWG were observed in treatm-ents T3 and T0 respectively (p<0.05). The highest CF was observed in T3 and the lowest was obtained in T0. All in all, this study proposed that the addition of 15 gr of hydro-alcoholic extract of Vitex agnus-castus in the diet of zebrafish could improve the performance of the growth indices and increase the final biomass. In addition, this extract could be considered as a suitable supplement for Cyprinidae diet.

---

This study was conducted in order to measure glucose, cholesterol and hematocrit as indicators to evaluate the effect of caraway seeds meal (CSM) on the health and resistance of common carp to salinity stress. To attain this goal, fish (2.457±0.057 g) were divided into four groups fed on diets containing different levels of CSM; 0 (control), 0.5, 1 and 1.5%. After 56 days of feeding, blood samples of the fish were obtained in five stages (once before and four times after stress) to evaluate glucose, cholesterol and hematocrit levels. The experiments indicated that salinity sign-ificantly affected glucose, cholesterol and hematocrit. On the first day after stress, the hematocrit and glucose levels were considerably increased in all groups compared with their levels before stress. After stress, cholesterol level signif-icantly decreased in all groups compared to before stress. The level of hematocrit indicated no significant difference among the groups before and after stress. On the first day after stress, the glucose levels significantly increased in trea-ted groups with CSM compared with the control group. The glucose and hematocrit levels were decreased gradually in all groups from the third day on. After stress, no differences were observed for survival rates among the experimental diets. However, the highest survival rate belonged to treated groups with CSM. The overall result indicated that the suplement of CSM has a positive influence on the glucose, hematocrit and resistance of common carp to salinity stress.

---

Fish oil in the diet of fish is constantly at the risk of oxidation. In this study, the effects of feeding sturgeon hybrid (Huso huso ♂ ×Acipenser ruthenus ♀) with different levels of oxidized fish oil (OFO) on thyroid hormones were investigated. Three experimental diets were made by replacing 0 (control), 50 and 100% OFO were made. Ninety hybrid sturgeon, with the initial weights of 212.6 ± 07g were distributed in 9 fiberglass tanks (2 m³) randomly after 2 weeks of adaptation with experimental conditions. Feeding was performed three times daily (08:00, 14:00 and 20:00) for 6 weeks for satisfaction. At the end of the period, blood samples were taken and their serum was separated. Serum thyroxine and triiodotyronine were measured by radioimmunoassay in blood samples. Serum thyroxine, triiodotyronine and thyroxine/triiodotyronine level showed no significant change related to dietary OFO. Our findings showed that dietary-oxidized oil had no effect on blood thyroid hormones levels.

---

Feeding frequency and stocking density are important factors affecting growth and maturation of cultured fishes. The aims of this investigation were to determine the effects of stocking density (10, 20, 30 and 40 fish per aquarium) and feeding frequency (2, 3 and 4 times per day) on growth parameters and hematocrit of the Rutilus rutilus caspicus. The experiment was continued for 45 days in two replicates. The results of this study showed that growth parameters, including weigh gain (WG), feed conversion ratio (FCR) and specific growth rate (SGR) were affected significantly by stocking density (P<0.05), but not significantly affected by feeding frequency (P>0.05). The highest WG and SGR were recorded with the lowest stocking density (10 fish / aquarium). The least FCR was obtained in density of 10 fish/aquarium, FCR value was significantly higher with high stocking density (P<0.05). Also, interactions between stocking density and feeding frequency were no significant on growth parameters (P>0.05). Density and feeding frequency hand no significant effect of hematocrit concentration (P>0.05). On the other hand, interactions between stocking density and feeding frequency significantly affected hematocrit levels (P<0.05). The lowest level of hematocrit was observed in density of 10 fish/aquarium at two times / day feeding frequency. The results of this study indicated that density is significantly affected the growth, but increasing of feeding frequency there is not effect on growth in the Rutilus rutilus caspicus.
 

---

In this study, the morphology and organization of the retina of Caspian kutum and fish response to ambient light as retinomotor reaction was investigated. The Rutilus frisii subsp. kutum is an anadromous fish and important native fish specimen of Caspian Sea. The specimens were obtained from Shahid Ansari Teleost Reproduction and Culture center (Guilan province, Iran). For light and dark adaptation fish were left in dark and light at least 30 minute prior to death. The eye retina were dissected out and processed for histological and SEM studies. The eye retina of Caspian kutum like most vertebrates, was composed of ten layers. Two types of photoreceptor cells including rod and short single cone were identified. Sagittal and transverse retinal sections did not show any particular patterns of cone arrangement. The retinomotor response observed in adapted retina to light and dark conditions revealed that Caspian kutum strongly reacts to changing light conditions. A remarkable pigment index indicated kutum relied mostly on rod rather than cone vision. The movement of pigment granules and slight change of cone myoid showed that the fish could recognize colors.

---

In order to investigate the differences in the shape of the big-head and two morphotypes of Phytophagous fish by geometric morphometric technique, 30 samples of each group, with a mean standard length of 25 ± 3 cm, were prepared. After fish were anesthetized by 1% Clove powder extract and stabilized in formalin buffer 4%, 6-megapixel digital images of the left profile of the specimens were prepared. A total of 17 morphological landmarks were digitized by tpsDig2 software and the tps files were prepared. All non-shaped data were removed from landmark coordinates by generalized procrustes analysis. After the approval of regression between shape space and tangent space, data were analyzed using Principal Component (PCA), Canonical Variation (CVA) and Cluster Analyzes (CA) methods in PAST and TPS series. According to the results, the head length and height, the size of dorsal fin, the length of pre ventral distance, the height of caudal peduncle and the degree of posterior position of the pectoral fin in bighead carp, are some of the distinctive morphological features among species, mainly related to their ecological niche (specially feeding strategies). In the case of silver carp variants, the posterior position of pectoral fin base in silver carp-R that is close to bighead carp, may be due to hybridization between bighead carp and silver carps.