Whole genome sequencing of Chinese clearhead icefish, Protosalanx hyalocranius

Background: Chinese clearhead icefish, Protosalanx hyalocranius, is a representative icefish species with economic importance and special appearance. Due to its great economic value in China, the fish was introduced into Lake Dianchi and several other lakes from the Lake Taihu half a century ago. Similar to the Sinocyclocheilus cavefish, the clearhead icefish has certain cavefish-like traits, such as transparent body and nearly scaleless skin. Here, we provide the whole genome sequence of this surface-dwelling fish and generated a draft genome assembly, aiming at exploring molecular mechanisms for the biological interests. Findings: A total of 252.1 Gb of raw reads were sequenced. Subsequently, a novel draft genome assembly was generated, with the scaffold N50 reaching 1.163 Mb. The genome completeness was estimated to be 98.39 % by using the CEGMA evaluation. Finally, we annotated 19 884 protein-coding genes and observed that repeat sequences account for 24.43 % of the genome assembly. Conclusion: We report the first draft genome of the Chinese clearhead icefish. The genome assembly will provide a solid foundation for further molecular breeding and germplasm resource protection in Chinese clearhead icefish, as well as other icefishes. It is also a valuable genetic resource for revealing the molecular mechanisms for the cavefish-like characters.

Effects of 17β-estradiol and 17α-ethinylestradiol on the embryonic development of the clearhead icefish (Protosalanx hyalocranius)

Estrogenic effects of 17β-estradiol (E2) and 17α-ethinylestradiol (EE2) on animals have been widely reported. The high sensitivity of fish in the early-life stages to xenobiotics can be exploited to evaluate the developmental effects of environmentally relevant levels of E2 and EE2. In this work, clearhead icefish (Protosalanx hyalocranius) embryos (blastula stage) were exposed to E2 or EE2 at concentrations between 0.05 ng/L and 1 mg/L. The toxicity endpoints of mortality, teratogenesis, and hatching retardation were evaluated. The results showed that continuous exposure of the fish embryos/larvae to higher concentrations of E2 and EE2 dramatically increased mortality after 17 days, when the hatching period started. An E2 concentration of 8 μg/L (day 16) and an EE2 concentration of at 0.2 mg/L (day 18) induced maximum teratogenesis rates of 30% and 35%, respectively. Embryos exposed to 0.2 mg E2 or EE2/L had a significantly retarded hatching time compared to the control. Thus, although environmentally relevant concentrations E2 and EE2 are not lethal for P. hyalocranius embryos or larvae, their ability to induce teratogenesis and hatching retardation merits concern.

Complete mitochondrial genome of clearhead icefish Protosalanx hyalocranius (Salmoniformes: Salangidae)

In this study, we sequenced and determined the complete mitochondrial genome of clearhead icefish (Protosalanx hyalocranius). The circular mitochondrial genome (16,693 bp) contained 13 protein-coding genes, 22 transfer RNA genes, 2 ribosomal RNA genes, and 1 control region. All genes were encoded on the heavy strand with the exception of ND6 and eight tRNA genes.

[Diet composition and transition of clearhead icefish(Protosalanx hyalocranius)in Lake Xingkai]

Diet compositions of alien clearhead icefish(Protosalanx hyalocranius)in Lake Xingkai were investigated monthly from June 2010 through January 2011. Protosalanx hyalocranius preyed mainly on cladoceran, copepoda, shrimp, and larvae or juvenile fish. In June, P. Hyalocranius were smaller than 60 mm standard length(SL), and their diets were composed of zooplankton only. In July, fish began to appear infrequently in the diet of P. Hyalocranius larger than 60 mm SL, and by August fish was occurring in the diets of P. hyalocranius larger than 80 mm, 100 mm in September, and 120 mm in October and thereafter, respectively. The increase in the minimum SL of P. hyalocranius preying on fish within a given season reflects changes in resource availability, largely attributed to the corresponding increase in prey fish size as seasons progress. Protosalanx hyalocranius and Hemiculter sp. were the dominant prey fish in the diets of P. hyalocranius.