No abstract

The purpose of this study was to develop a practical protocol for the production of female populations of Arctic charr (Salvelinus alpinus). Achieving this required knowledge of the timing of gonadal differentiation. Undifferentiated gonads were observed microscopically to be present by 194 degrees C-days post-hatch and definitive germ cells by 346 degrees C-days post-hatch, where " degrees C-days" denote acquired thermal units calculated as the product of temperature and days. Some of the gonads had developed a lumen by 510 degrees C-days post-hatch, and by 681 degrees C-days post-hatch anatomical divergence into two types of gonads was clear. Two protocols (immersion and feeding) were tested for hormonal sex reversal of genotypic females using the synthetic androgen 17alpha-methyldihydrotestosterone (MDHT). Six-hour MDHT immersions (0.5, 1, 3, 5 and 10 mg/L) were carried out weekly from hatch to first feeding (140 degrees C-days post-hatch), whereas daily feeding treatments (0.5 mg/kg) went from 140 to 600 degrees C-days post-hatch. The sex ratios of all immersion experimental groups were significantly different from the control, with the proportion of presumptive males increasing as MDHT concentration increased. The highest immersion treatment, 10 mg/L, yielded a population of 90% presumptive males and 10% with atypical gonads. However, the most effective treatment, yielding a population of 90% presumptive males and no fish with atypical gonads, was the feeding treatment. Given that female salmonid fishes are homogametic, sex-reversed (masculinized) genotypic females produced in this way can serve as broodstock for the creation of all-female charr populations for aquaculture.

A study was conducted on 500 juvenile rainbow trout (122 ± 4 g) fed either a control diet or a treatment diet containing 300 mg/kg of a microencapsulated blend of organic acids and essential oils to elucidate effects on intestinal morphology and microbiome. Proximal intestinal villi length was significantly increased in fish fed the treatment diet. Despite no differences in gut inflammation scores, edema, lamina propria inflammation and apoptosis were completely absent in the distal intestine of fish fed the treatment diet. Next-generation sequencing of the 16S rDNA showed no differences in alpha and beta diversity, and gut bacteria were mainly composed of Firmicutes, Bacteroidetes and Proteobacteria. On the genus level, LefSe analysis of indicator OTUs showed Bacteroides, Sporosarcina, Veillonella, Aeromonas and Acinetobacter were associated with the control diet whereas Streptococcus, Fusobacterium and Escherichia were associated with the treatment diet. Aeromonas hydrophila and Acinetobacter spp. are opportunistic pathogens and several strains have been found to be resistant to antibiotics. The increase in villi length and reduction of specific pathogens indicates that feeding a microencapsulated blend of organic acids and essential oils improves gut health and may serve as a part of an effective strategy to reduce antibiotic use in aquaculture.

To determine the potential for genetic improvement in Fraser strain Arctic charr (AC, Salvelinus alpinus), we calculated genetic parameters for BW and condition factor (K) and tested if previously identified QTL for these traits were detectable across a commercial broodstock reared in both freshwater (FRW) and brackish water (BRW). Individuals from 30 full-sib families were reared up to 29 mo of age in FRW and BRW tanks at a commercial facility. Heritability for BW and K was moderate in FRW (0.29 to 0.38) but lower in BRW (0.14 to 0.17). Genetic correlations for BW across environments were positive and moderate (0.33 to 0.67); however, equivalent K correlations were very weak (0.24 to 0.37). We identified a single BW QTL with experimentwide effects on linkage group AC-8, 4 BW QTL (AC-4, -13, -14, and -19), and 3 K QTL (AC-4, -5, and -20) with chromosomewide effects across families. Notably, the QTL on AC-8 had significant effects with BW at 3 out of 4 sampling dates in FRW and had significant allelic phase disequilibrium with BW across families, suggesting a tight coupling of the marker region to the QTL in this population. Body weight QTL were identified on AC-4 in both FRW and BRW environments and AC-4 was the only linkage group with a detectable QTL for both K and BW. Modest consistency of some QTL effects as well as moderate heritability in both environments suggests that there is some potential for genetic improvement of growth in this species even though gene × environment interactions are high.

. 2008. Gonadal differentiation in Atlantic cod, Gadus morhua L., and haddock, Melanogrammus aeglefinus (L.). Acta Ichthyol. Piscat. 38 (2): 127-133.Background. The purpose of this study was to determine the timing of gonadal differentiation in two gadoids: Atlantic cod, Gadus morhua L., and haddock, Melanogrammus aeglefinus (L.). This information is required to develop a practical protocol for the production of monosex populations of these species for aquaculture. Materials and Methods. Cultured larvae and juveniles were collected weekly, measured (total length; TL), prepared histologically and then examined microscopically for the presence of characteristic stages of gonadal differentiation. Results. In Atlantic cod, undifferentiated gonads were present by 18 mm TL, at 84 days post hatch (dph), and definitive germ cells by 19 mm TL (90 dph). Ovarian cavities were first observed at 27 mm TL (102 dph), and by 35 mm TL (112 dph) anatomical divergence into two types of gonads was clear. In haddock, undifferentiated gonads were observed at 21 mm TL (64 dph) and an ovarian cavity was evident at 29 mm TL (71 dph). Conclusion. Gonadal differentiation in Atlantic cod and haddock occurs at roughly the same size in both species (27 and 29 mm TL, respectively). For successful sex reversal, the administration of steroids should therefore begin at approximately 25 mm TL, shortly after weaning onto dry feed.