No abstract

In order to determine the Oligochaeta fauna of the Anzali International Wetland (northwestern Iran), samples of bottom sediment and aquatic vegetation were collected from 13 stations eight times from August 2012 to June 2013. As a result of the study, 11 species and one genus were identified: Tubifex tubifex, Limnodrilus claparedeianus, L. hoffmeisteri, Potamothrix hammoniensis, P. bedoti, Branchiura sowerbyi, Nais pardalis, Ophidonais serpentina, Dero digitata, Stylaria lacustris, Slavina appendiculata, and Mesenchytraeus sp. Some physico-chemical parameters of the water (depth, temperature, dissolved oxygen, and pH) were measured at the sampling site. The average density of the total oligochaete community in the benthos of the wetland was 6077 ind. m -2 . The Shannon-Wiener diversity index was on average 0.92, with a maximum of 1.57 and a minimum of 0.44 at different stations. Results indicated that the maximum and the minimum density were observed in June (21 837 ind. m -2 ) and in December (1041.9 ind. m -2 ), respectively. Most frequent and abundant species were the tubificids L. hoffmeisteri, L. claparedeianus, and P. hammoniensis. All determined oligochaete taxa except T. tubifex were new to the Anzali Wetland, including seven new to the fauna of Iran. The structure of the Oligochaeta community correlated with the progression of the trophic state of the aquatic ecosystem.

The series of reproductive events in various species of Gammaridae can be described as precopula, copula, egg deposition and fertilization, hatching of the newborn, and the presence of young individuals. The stages of Pontogammarus maeoticus were explored in the laboratory. Amphipod samples were collected on the southwestern coast of the Caspian Sea (Jefrood Beach). The animals were transferred to the laboratory along with sediment from their habitat. The samples were maintained under controlled laboratory conditions at a temperature of 25 ± 1°C, a salinity of 9 ± 0.5‰ and in a 12 : 12 h light/dark regime for about six weeks. In this study, we examined the species’ reproductive sequence. The average time spent in the precopula stage was approx. 2.6 ± 0.91 days and embryonic development took about 8.5 ± 1.1 days. Fecundity was estimated as the number of fertilized eggs existing in the brood pouch of each female (average 14.12). The average length of females was recorded as 12.21 mm. The first precopula was observed about 40 days after hatching. The species has a relatively short reproductive cycle and the generations are able to reproduce after a short period (about 40 days). Hence, this species seems to be a good choice for potential use in aquaculture.

No abstract

Teleosts account for more than half of the vertebrate species. A key feature of the evolutionary success of teleosts is their reproductive systems, which are efficient and functional under all aquatic environmental conditions. The zona radiata (ZR) is a non- cellular envelope over oolemma of teleost fish oocytes. The morphology of the ZR varies in different ovarian developmental stages and also among various fish species, which reflects adaptation to ecological conditions. In this research the structure of the ZR in the oocytes of zebrafish in different stages of ovarian development and oocyte growth were studied. The fish ovary was fixed in Bouin's solution. Histological sections were studied by light and scanning electron microscope after subjecting them to tissue preparation stages. In immature and primary growth stages (I and II), the ZR was not observed. In stage III, the ZR was observed as a thin layer around the oocyte. It increased in thickness at stage IV (vitellogenesis) but reduced in stage V (maturation). In early stage III, the ZR striations started to appear and in stage IV (vitellogenesis) fence-like striations were completely formed. SEM micrographs showed stria to be deep with crenelated margin. In late stage IV fence-like striations disappeared gradually and in matured egg (V) the stria turned into pit-like remnants. In zebrafish no adhesive filaments were observed and the ZR surface was smooth.