The physiological condition of the female reproductive tract reflects the requirements of the early mammalian embryo. In the human oviduct and uterus, concentrations of carbohydrates differ between ovulation and the time of implantation. Amino acids are involved throughout preimplantation development. Hyaluronan is also present in the reproductive tract and is involved in different processes. It has been shown that culture of embryos in media containing hyaluronan improves cryosurvival, /.e. results in an increased viability after thawing. Overall, embryo requirements differ for the pre- and post-compaction embryo. As a consequence, to meet the needs of human embryos, culture conditions have to be adapted to the developmental stage. Optimized human embryo culture in vitro requires physiological conditions from the moment of oocyte collection until the replacement of the embryo. A new media system, the GILL Series™, has been developed taken into account the changes in embryo physiology and requirements which occur as the embryo develops from the oocyte to the blastocyst stage. Results form different clinics have shown that high pregnancy and implantation rates can be obtained using the GILL Series™. As compared to the previous media (G1.2/G2.2), Gardner et al. (Fertile. Steril., 78 (Suppl. 1), S8, 2001) reported an increased clinical pregnancy rate (from 69.8 % to 78 %) and an increased implantation rate (from 46 % to 53 %), for day 5 embryo transfers with the GILL Series™. Comparing the same culture systems, Balaban et al. (RRM online, 10, 485-491, 2005) reported an increase from 37.8 % to 50.3 % and from 14.5 % to 25.7 % for clinical pregnancy and implantation rate respectively for day 3 embryo transfers. For day 5 transfers the respective rates increased from 51.4 % to 69.4 % and from 29.0 % to 45.1 %. For embryos cultured in the presence of hyaluronan before ryopreservation Balaban et al. also reported increased development in vitro between thawing and replacement (from 26.2 % in G1.2-G2.2 to 58.3 % in GILL) as well as increased clinical implantation (from 7.8 % in G1.2-G2.2 to 15.1 % in GILL). The improvement of the in vitro environment allows performing single embryo transfer with good success rates. A clinical pregnancy rate of 36.9 % and an implantation rate of 32.1 % have been reported in a programme where an average of 1.2 embryos (75 % single embryo transfer) was replaced on day 2. Based on the latest research, the GILL series has been developed to minimize stress to oocytes and embryos and to culture them under physiological conditions. Clinical results obtained by different clinics confirm that large numbers of embryos can develop in vitro and further develop to term after replacement on different days of development.

The ontogeny of the GILL structure in starlet (Acipenser ruthenus) was studied histologically from hatching up to 50 days post hatching (dph). Based on the obtained results, the first developmental phase of the biological systems in this species was started from hatching with an intense organogenesis and the second phase from 9 dph with the beginning of exogenous feeding. The GILL anlage was visible in the pharyngeal region at 1 dph. The mouth and GILL slits opened at 2 dph along with the formation of four pairs of the primordial GILL arches. At 3 dph, the primordial GILL filaments formed. The development of the primordial lamellae and pseudobranch were observed at 8 dph. The primordial GILL filaments of the pseudobranch were appeared at 9 dph. The chloride cells appeared at 8 dph on the base of the GILL filaments. The GILL structure of the sterlet larvae at 31 dph was similar to that of the adults. The results of this study provided a proper indicator for aquaculture practice of starlet.

Background: Histological studies in organs like hepatopancreas and GILL of the freshwater fish, Cyprinus carpio, were made to assess tissue damage due to sub-lethal concentration of cadmium after a long exposure period.Methods: This study was conducted in University of Tehran, in 2013. The fish were divided into two groups in 1000 litre fiberglass tanks supplied with dechlorinated water [hardness 302.6 mg CaCo3/l, pH 7, O2 7.8 mg/L and temperature 15 ± 2oC] and continuous aeration. Group 1 was without any cadmium considered as control group. Group 2 was exposed to 30 ppb CdCl2 (Merck) containing 7.8 ppb cadmium. The tissue samples from: hepatopancreas, GILL were collected 30 days post exposure and processed by histological procedures.Results: The main lesions in cadmium exposed groups were: (a) pancreatitis necrosis in endocrine part of pancreas (b) cholangitis and necrosis in liver parenchyma (c) hypertrophy, fusion and telangiectasia in secondary lamellae Conclusion: Cadmium chloride at low concentration can induce pathological alterations in hepatopancreas and GILL of common carp.