No abstract

Owing to the demand for sustainable sex-control protocols in aquaculture, research in tilapia sex determination is gaining momentum. The mutual influence of environmental and genetic factors hampers disentangling the complex sex determination mechanism in Nile tilapia (Oreochromis niloticus). Previous linkage analyses have demonstrated quantitative trait loci for the phenotypic sex on linkage groups 1, 3, and 23. Quantitative trait loci for temperature-dependent sex reversal similarly reside on linkage group 23. The anti-Müllerian hormone gene (amh), located in this genomic region, is important for sexual fate in higher vertebrates, and shows sexually dimorphic expression in Nile tilapia. Therefore this study aimed at detecting allelic variants and marker-sex associations in the amh gene. Sequencing identified six allelic variants. A significant effect on the phenotypic sex for SNP ss831884014 (p<0.0017) was found by stepwise logistic regression. The remaining variants were not significantly associated. Functional annotation of SNP ss831884014 revealed a non-synonymous amino acid substitution in the amh protein. Consequently, a fluorescence resonance energy transfer (FRET) based genotyping assay was developed and validated with a representative sample of fish. A logistic linear model confirmed a highly significant effect of the treatment and genotype on the phenotypic sex, but not for the interaction term (treatment: p<0.0001; genotype: p<0.0025). An additive genetic model proved a linear allele substitution effect of 12% in individuals from controls and groups treated at high temperature, respectively. Moreover, the effect of the genotype on the male proportion was significantly higher in groups treated at high temperature, giving 31% more males on average of the three genotypes. In addition, the groups treated at high temperature showed a positive dominance deviation (+11.4% males). In summary, marker-assisted selection for amh variant ss831884014 seems to be highly beneficial to increase the male proportion in Nile tilapia, especially when applying temperature-induced sex reversal.

Flesh characteristics of pan-size triploid and diploid rainbow trout (Oncorhynchus mykiss) reared in a commercial fish farm AbstractSexual maturation of rainbow trout during production has a negative effect on the slaughter yields and flesh quality. Induction of triploidy is a method to prevent the development of fertile trout. In many investigations sexually mature triploid and diploid rainbow trout had been compared. In the present study the slaughter characteristics and flesh quality of female immature diploid and triploid rainbow trout reared up to 66 and 75 weeks (pan-size-format) were compared. Considering the age the old fish had significantly higher body and fillet weights accompanied with larger muscle fibres. The fillets of the old trout were brighter and redder, had a reduced water-holding capacity (WHC) and contained more fat and protein. With regard to the ploidy status the triploid trout had higher body and fillet weights and larger muscle fibres. The fillets of the triploid fish were brighter, had a reduced WHC and lower fat contents. With regard to the age-ploidy status interaction the young and old triploid trout had better growth characteristics but the WHC and the fillet fat concentration was reduced in these animals. The colour values were inconsistent. The pH and electrical conductivity values indicated no higher pre-or peri-mortal stress and/or different stress susceptibility of the investigated young as well as old triploid and diploid trout. In conclusion, it could be suggested that induction of triploidy positively influences body and fillet development mainly by muscle fibre hypertrophy, but the triploid fillets showed slightly worse flesh characteristics (Brightness, WHC).

Juvenile noble crayfish, Astacusastacus (Crustacea, Astacidea) in the second year of age were kept in the laboratory for a twelve-month period under continuing “summer conditions” (LD 16:8, 19°C). Molting processes in this population could be synchronized by artificial moonlight cycles. Peaks of exuviations occurred at “new moons”. Males showed a slightly higher degree of synchronization than females. A phase-shift of the artificial lunar cycle in relation to the natural cycle resulted in a corresponding shift of the molting cycle. This clearly demonstrates that changes in the nocturnal light regime provide the primary external information for the lunar-monthly molting rhythm. There is a first indication that lunar photic stimuli do not act directly but as a zeitgeber which entrains an endogenous molting rhythm to the lunar cycle. Moreover, the results of the long-term experiments suggest that the hibernal resting period of A . astacus in the field (no molts between October and April) may also involve some endogenous programming. Continuing artificial summer conditions can delay but not completely suppress this resting period. The adaptive significance of the phenomena and how the findings may be applied to improve the management of crowded crayfish stocks are discussed.

In teleosts, elevated temperature during embryogenesis can act on germline cell development, which in turn plays a role for sexual fate. In Nile tilapia, a species with high-temperature-induced masculinization, little is known about the effects of increased temperature on gonadal development in non-masculinized females. The aim of the present work was to investigate persistent effects on the germline of genetically female (XX) Nile tilapia reared at normal (28°C) or elevated temperature (36°C) during the critical time of gonadal sex differentiation at 10 to 20 days post fertilization. Non-sex-reversed females were compared to control females to determine persistent effects of temperature on subsequent ovarian development using histological approaches. Germline stem cells were identified using the germline marker Vasa in combination with the proliferation marker PCNA. Vasa- and PCNA-positive germline stem cells were found in ovaries of both high-temperature-treated and control females. In both groups, ovarian germline stem cells were located at the germinal epithelium of the ovigerous lamellae. Although no detrimental effects of high temperature on gonadal development in female Nile tilapia were observed, implications on the reproductive fitness caused by elevated temperature need to be investigated in greater depth.