Carotenoids and retinoids in the gonad of brood-stock pikeperch: accumulation during vitellogenesis and influence on egg quality in farmed pikeperch Sander lucioperca.

Carotenoids are determinants of reproductive fitness and egg quality. Here we studied the accumulation of astaxanthin (AX), canthaxanthin (CA) zeaxanthin (ZX), lutein (LU), retinol (RX) and dehydroretinol (DR) during vitellogenesis comparing previtellogenic and vitellogenic pikeperch (Sander lucioperca) eggs (n = 5 each), as well as selected tissues (liver, fat and muscles) in first süawning females (1176-1450 g). Futhermore, we compared egg batches with high (88-99% hatching rate, n = 5) or low (40-67% hatching rate, n= 5) egg quality. Vitellogenic follicles revealed higher concentrations of DR, RX, ZX and LU compared to previtellogenic follicles. Neither CA nor AX was detectable. In parallel, DR and RX were mobilized in the liver. In adipose and muscle tissue, comparing previtellogenic and vitellogenic females, no significant differences in carotenoid/retinoid content were observed. In high quality egg batches, both DR and RX were increased. LU was lower in high quality than in low quality eggs. In a conclusion, the amount of retinoids seems suboptimal in low quality egg batches and increased DR and RX are desirable in pikeperch. Since hypervitaminosis of retinoids can be problematic though, supplementation of the food with carotenoids, which can serve as precursors for retinoids, has to be carried out carefully.

Ion-rich potash mining effluents affect sperm motility parameters of European perch, Perca fluviatilis, and impair early development of the common roach, Rutilus rutilus.

Secondary salinization of freshwater ecosystems is of increasing global concern. One of the main causes are the effluents of the potash mining industry containing high concentrations of major ions (Cl-, Na+, Mg2+, K+). In Germany, the ongoing discharge of effluents into the River Werra led to a strong impoverishment of the biodiversity and abundance of local species. Young cohorts of many freshwater fish are completely absent suggesting reproductive failure under these conditions. Therefore, the aim of the study was to experimentally investigate the effects of high concentrations and imbalances of ions that are prevalent in potash mining effluents on reproductive traits of native freshwater teleosts. Sperm motility parameters of the common roach, Rutilus rutilus, and European perch, Perca fluviatilis, were assessed as well as fertilization rate, egg size, hatching, malformations and mortality of embryonic and larval stages of roach. Concentrations of the permitted thresholds (HT) and future thresholds (LT) as well as three ion solutions containing high Mg2+ (Mg), high K+ (K) and both in combination (Mg + K) were tested. Curvilinear velocity and linearity of perch spermatozoa were elevated with potentially adverse effects on fertilization success. Sperm motility parameters and fertilization rate of roach were not affected. However, egg sizes of roach were increased in all groups due to the osmotic action of ions and in LT, premature hatch was observed. Furthermore, all groups comprised a higher number of malformations including pericardial edema and spine curvatures and group HT exhibited a higher mortality rate compared to control. The results clearly demonstrated that particularly the sum of high concentrations of ions, as prevalent in HT and LT, rather than individual ion species exerts detrimental effects on early development of roach potentially increasing overall mortality under natural conditions. These results emphasize that currently permitted and future thresholds are exceeding tolerated ion concentrations.

A duplicated copy of id2b is an unusual sex-determining candidate gene on the Y chromosome of arapaima (Arapaima gigas).

Arapaima gigas is one of the largest freshwater fish species of high ecological and economic importance. Overfishing and habitat destruction are severe threats to the remaining wild populations. By incorporating a chromosomal Hi-C contact map, we improved the arapaima genome assembly to chromosome-level, revealing an unexpected high degree of chromosome rearrangements during evolution of the bonytongues (Osteoglossiformes). Combining this new assembly with pool-sequencing of male and female genomes, we identified id2bbY, a duplicated copy of the inhibitor of DNA binding 2b (id2b) gene on the Y chromosome as candidate male sex-determining gene. A PCR-test for id2bbY was developed, demonstrating that this gene is a reliable male-specific marker for genotyping. Expression analyses showed that this gene is expressed in juvenile male gonads. Its paralog, id2ba, exhibits a male-biased expression in immature gonads. Transcriptome analyses and protein structure predictions confirm id2bbY as a prime candidate for the master sex-determiner. Acting through the TGFß signaling pathway, id2bbY from arapaima would provide the first evidence for a link of this family of transcriptional regulators to sex determination. Our study broadens our current understanding about the evolution of sex determination genetic networks and provide a tool for improving arapaima aquaculture for commercial and conservation purposes.

Pikeperch Sander lucioperca egg quality cannot be predicted by total antioxidant capacity and mtDNA fragmentation.

In farmed pikeperch, there is a high variability in egg quality restraining the propagation of this species in aquaculture. The identification of reliable biomarkers for predicting successful embryo development already at an early stage (unfertilized oocyte) could help improve production efficiency. Total antioxidant capacity (TAC) and the quantification of mitochondrial DNA (mtDNA) fragmentation have been established as biomarkers for oxidative stress and damage of macromolecules, potentially influencing embryo development. Therefore, we evaluated these biomarkers in eggs of commercially farmed pikeperch (44 females). We measured egg TAC, as well as lesion rates per 10 kb of 12S and cytochrome b (cytb) as target regions within the mitochondrial genome by qPCR. It was tested whether these markers correlate with embryo development (fertilization rate, embryo survival, hatching rate). There was no significant relation of mtDNA lesion rates or TAC with these egg quality parameters. We detected average lesion rates (± SD) of 1.50 (± 1.57) and 1.89 (± 2.14) in 12S and cytb mtDNA respectively. Lesion rates in 12S and cytb were highly correlated within samples (P < 0.0001) and were independent of the observed TAC. The results suggest that TAC does not prevent mtDNA fragmentation and that embryos rather seem to be able to cope with the observed fragmentation of mtDNA. However, in post-ovulatory aged eggs of three females with little to no fertilization success, lesion rates of cytb were significantly elevated, whereas TAC was significantly lower compared to other females, suggesting a possible role of oxidative stress during post-ovulatory ageing.