Evidence for genetic distinction among sympatric ecotypes of Arctic char (Salvelinus alpinus) in south‐western Alaskan lakes

Resource polymorphism may play an important role in the process of speciation. The Arctic char (Salvelinus alpinus) exhibits great phenotypic and genetic diversity across its range, making it an ideal species for studies of resource polymorphism and divergence. Here, we investigated genetic variation at 11 microsatellite loci among 287 Arctic char from five isolated yet proximate postglacial lakes in south‐western Alaska that were previously examined for resource polymorphism. Significant differences in pairwise F_ST were detected among all lakes (range from 0.05 to 0.28, all P < 0.02). In one lake (Lower Tazimina Lake), we found evidence for two genetic groups of char and for significant differences in the distribution of microsatellite variability among at least two of the three previously described body size morphotypes (‘large’‐, ‘medium’‐, and ‘small’‐bodied char; maximum F_ST = 0.09; differences in admixture proportions). We also found a significant association between genetic admixture proportions and gill raker counts among body size morphs (r = ?0.73, P < 0.001). Our data represent the first record of genetically distinct sympatric morphs of Arctic char in Alaska and provide further evidence that differences in morphology associated with feeding (gill rakers) and growth trajectories reflect niche diversification and promote genetic divergence in Holarctic populations of Arctic char.     

Effects of dietary selenium on growth performance and oxidative stress in juvenile grass carp Ctenopharyngodon idellus

An 8‐week feeding trial was conducted to investigate the effect of dietary selenium (Se) on feed intake, weight gain and antioxidant activity in juvenile grass carp (11.2 ± 0.03 g). Six Se levels (0.13, 0.41, 0.56, 1.12, 2.18 and 4.31 mg/kg) of semi‐purified diets were assayed in triplicate. The maximum weight gain, specific growth rate and feed intake were obtained in fish fed with 1.12 mg Se/kg diet. Hepatic glutathione peroxidase activity was markedly increased when dietary Se ≤1.12 mg/kg diet and reached a plateau when dietary Se ≥1.12 mg/kg diet. Hepatic superoxide dismutase and serum catalase activities in juvenile grass carp fed with 0.56, 1.12 and 2.18 mg Se/kg diets were all significantly higher than those in the other groups. The malondialdehyde content in liver and serum was firstly decreased and then increased with increasing dietary Se content, and the lowest content was observed in fish fed with 1.12 mg Se/kg diet. With the increase in Se level, the activities of serum alanine aminotransferase and aspartate aminotransferase were reduced. In addition, serum alkaline phosphatase activity and albumin content were highest in fish fed with 1.12 mg Se/kg diet. This study indicated that both the Se deficiency and excess of Se caused negative effect on the oxidative stress in juvenile grass carp and suggested that the health‐giving concentration of dietary inorganic Se was 1.12 mg/kg diet. Moreover, based on the broken‐line regression analysis of weight gain, the optimal concentration of dietary inorganic Se was 0.83 mg/kg for juvenile grass carp.     

First report of Fusarium oxysporum species complex infection in zebrafish culturing system

Fusarium oxysporum species complex (FOSC) is a highly diverse fungus. Recently, F. oxysporum infection was identified from zebrafish (Danio rerio) culturing system in Korea. Initially, a rapid whitish smudge was appeared in the water with the fungal blooming on walls of fish tanks. Microscopic studies were conducted on fungal hyphae, colony pigmentation and chlamydospore formation and the presence of macro‐ and microspores confirmed that the isolated fungus as F. oxysporum. Furthermore, isolated F. oxysporum was confirmed by internal transcribed spacer sequencing which matched (100%) to nine F. oxysporum sequences available in GenBank. Experimental hypodermic injection of F. oxysporum into adult zebrafish showed the development of fungal mycelium and pathogenicity similar to signs observed. Histopathologic results revealed a presence of F. oxysporum hyphae in zebrafish muscle. Fusarium oxysporum growth was increased with sea salt in a concentration‐dependent manner. Antifungal susceptibility results revealed that F. oxysporum is resistant to copper sulphate (up to 200 μg mL^?1) and sensitive to nystatin (up to 40 μg mL^?1). This is the first report of FOSC from zebrafish culture system, suggesting it appears as an emerging pathogen, thus posing a significant risk on zebrafish facilities in the world.     

A spatiotemporal study of bacterial community profiles associated with Atlantic bluefin tuna larvae,Thunnus thynnus L., in three Mediterranean hatcheries

During the first 2 years of larval rearing trials with Atlantic bluefin tuna, survival was a challenging issue. As bacterial colonization of the gut has been shown to play a key role for other species, we studied the profiles of the microbiota associated with individual larvae at different stages in three distant hatcheries. The Bacterial Community Profile (BCP) was quantified based on PCR‐DGGE analyses of partial amplicons from 16S rDNA. Considerable individual variability in BCP was observed before onset of feeding, and the BCP did not show regular fluctuation during ontogenesis. Microalgae were added to the rearing tanks in two of the three hatcheries, but it was not possible to distinguish the effect of location from the effect of algal addition on BCP. In one hatchery, the larvae were reared either with algal addition or in mesocosm, but due to high individual variability, no significant difference in BCP was detected between the two groups. It was hypothesized that this variability was caused by differences in health, physiological status and developmental stage of the larvae. A practical conclusion from the study is the need to analyse a considerable number of individuals to reflect statistically significant differences between the microbial communities associated with rearing groups.