The diet of the Scaly Whipray, Himantura Walga, in Persian Gulf coasts, Hormozgan Province was investigated through stomach content analysis. Two major and two minor prey groups were identified. The diet of H. Walga was dominated by crustaceans. The Index of food preference indicated that shrimps and crabs were the most important prey groups consumed, representing 79.35% and 51.09% of the diet respectively. Sea urchin (17.39%) and small zoobenthos (7.84%) were minor dietary components. Analysis of stomach contents for H. Walga revealed that diet did not vary with season. This stingray is a carnivorous fish based on intestine relative length index and stomach contents. Analysis of seasonal variation in the stomach fullness indicated that feeding intensity fluctuated throughout the year, with the highest value in spring. Vacuity index indicated this species was of voracious appetite fishes. Meanwhile, the feeding intensity increased with increasing in size.

In this research, histological structures of different parts of kidney (trunk and head kidney) were described in 21 fish species from northwest regions of the Persian Gulf. Fishes were anesthetized and then their kidneys with some adjacent vertebral column were collected and fixed in Buin’ s solution for histological purposes. Samples were processed according to routine paraffin method sectioned (5 micrometers) and stained (Hematoxylin and Eosin). According to the results, kidneys have two distinct structures including hematopoietic and excretory tissues. Head kidney has more hematopoitic role with nephrons among them. Different types of blood cell such as red blood cells, lymphocytes, monocytes and granolocytes as well as plasmacells, reticular cells and macrophages were observed in head kidney. There were melanomacrophage bodies among hematopoietic tissues in some species. Excretory parts in studied species were included of glomerules and nephric tubules. Neck section, proximal tubule (I and II), distal tubule and collecting tubule were present in nephric tubules. In chondroichthyes such as Grey Bamboo Shark (Chiloscyllium griseum) and Stingray (Himantura walga) nephrons have bigger parts in comparison with osteichthyes due to evolutionary aspects.

Introduction Dasyatidae is primarily a marine subfamily, which is most common in shallow tropical waters. The species of this family are distributed worldwide; from tropical to warm temperate; Atlantic (Including the Mediterranean Sea), the Indian, and Pacific Ocean (Nelson, 2006). Six genera, Dasyatis (synonyms Trygon and Urolophoides), Himantura, Pastinachus (synonym Hypolophus), Pteroplatytrygon, Taeniura, and Urogymnus, with about 68 species are included in this family (Compagno, 2005).

The present study was conducted in order to obtain the necessary information on the diversity, abundance and distribution of macroinvertebrates, as well as to investigate the grazing status of batoid fishes (stingrays) from benthic macroinvertebrtes in coastal waters of Hormozgan province. For this purpose, sampling was done in the years 2017 and 2018 and once every year in the autumn season. At the end of the identification process, a number of 125 genus and 104 species belonging to 85 families, 31 classes, 9 orders, and 7 phyla were successfully identified. Results revealed that Malacostraca was the frequent order in the studied area. In order to investigate the possible relationship between composition and abundance of benthic macroinvertebrte and stingrays, CCA analysis was employed. Results of stomach content of stingrays revealed that in the diet of M. randall, crustacean (93.25 %IRI) has the highest amount. This pattern was the same for M. gerrardi and H. walga. However, in M. gerrardi, bivalvia were in the first place of importance (31.33 %IRI). Also, trophic level analysis was done for three species which shows all species are Mesopredators that place in the same level of food web. According to the mentioned cases, some benthic macroinvertebrates identified in this research have a significant  relationship with the benthic fishes, which requires more studies to investigate their relationship.

We assessed concentration of heavy metals (ell, Fe, Hg and Zn) in the muscular tissue of benthic species Himantura gerrard and pelagic species Selar crumenophthalmu s caught from the Persian Gulf during winter 2008. After biometrical measurements, the muscle tissues of 51 randomly selected samples were separated from 86 stations. Specimens were digested using the wet method and the concentrations of ell, Fe and Zn were determined using Atomic Absorption Spectrophotometer (flame method) and also concentration of mercury was determined using Mercury Analyzer device. The mean concentration of heavy metals in muscle tissues of Himantura gerrardi were as follows: Fe: 74.78; Hg: 0.77; Zn: 875.99 and Cu: 3.5. However, these values for muscle tissues of Selar crumenophthalmus were: Fe: 25.07; Hg: 0.20; Cu: Zn: 15.54 and Zn: 2.31mg/g dry weight. Results showed that concentration of the selected heavy metals in H gerrardi, were significantly higher than S. crumenophthalmus (p£0.05).

The biomass of batoidfishes biomasses (rays and skates) was estimated during November and December 2005 in Hormuzgan provincial waters (between Ras Meidani in the Oman Sea and Ras Naiband in the Persian Gulf). The total biomass was 12454 tons. Furthermore, the estimated biomass for depth layers 10-20, 20-30 and 30-50 meter were 7567, 1966231 and 292 tons, respectively.In addition, the biomass, CPUA and CPUE rates were also evaluated for each species in different depth layers. Himantura gerrardi with 6065 tons in depth layer 10-20 meter and Torpedo sp. with 0.6 ton in depth layer 20-30 meter had maximum and minimum biomass, respectively, among all the specimens. The number per area, mean weight and catch per unit area of batoidfishes in different depth layers were statistically analysed at 95 percent confidence.The number and catch per unit area of Himantura gerrardi significantly differed (P<0.05) between depth layers 30-50 meter and deeper than 50 meter, but not for other species (P>0.05).

Rays have high stocks in the Persian Gulf and Oman Sea, and are caught as by-catch in different fishing gears. Yield and Quality of gelatin extracted from the skin of dominant ray species of Persian Gulf, included: Butterfly ray (Gymnura  poecilura), Sting ray (Himantrura gerrardi), Honeycomb Sting ray (Himantura uarnak) and Eagle ray (Aetomylaeus maculatus), were studied. Biometric results and the mean of skinning yield for each species were reported. Skinning yield for Eagle ray was 3.2% that was significantly lower than other species (with > 60%). Gelatin, extraction was done in constant conditions by Chloridric acid pretreatment. The results of qualitative identification of samples were positive and according to standards, concluded that the extracted products were gelatin. Also, total nitrogen, humidity and pH of samples were in standard limits, but ash content was upper than maximum standard level. Minimum concentration of extracted gelatins for gel formation was 2% and no significant differences were observed between extracted gelatin samples. Melting temperature of rays gelatins ranged 20-25°C.Maximumand minimum yield of gelatin extraction yield were 20.4% and 19.0%, respectively. No significant difference were observed between gelatin extraction yield of four ray species (P>0.05). Results suggested that for industrial uses, the skin of different ray species can be mixed and use together.