Plasma cortisol and production of miRNAs in red drum (Sciaenops ocellatus) exposed to three distinct challenges.

The red drum Sciaenops ocellatus is a marine fish species of high commercial interest. Despite improvements in current aquaculture practices, there are still concerns about the impact of daily manipulations regarding fish welfare. To investigate how does fish respond to various challenges, S. ocellatus juveniles were submitted to two acute challenges, namely a confinement stress and a cold-temperature shock, as well as a chronic stress challenge consisting of 18 days of repetitive challenge events. The level of cortisol produced by individuals was used as a measure of activation hypothalamic-pituitary-interrenal (HPI) axis. A significant increase in cortisol levels was detected only after the confinement stress. Interestingly, the fish exposed to a chronic stress for 18 days exhibited cortisol levels significantly lower than those of non-challenged fish. The small RNA-sequencing conducted for the chronic stress experiment only allowed us to identify two plasmatic microRNAs more abundant in non-challenged fish (miR-205-1-5p and let-7b-5p) compared to challenged fish. The miR-205-1-5p was of particular interest since it was already detected in previous studies on other fish species. In silico analysis allowed to predict potentially highly conserved mRNA targets of this specific miRNA, among which is tnfrsfa that plays a key role in the secondary stress response.

Estradiol-17ß and bisphenol A affect growth and mineralization in early life stages of seabass.

Natural and synthetic estrogens are contaminants present in aquatic ecosystems. They can have significant consequences on the estrogen-sensitive functions of organisms, including skeletal development and growth of vertebrate larvae. Synthetic polyphenols represent a group of environmental xenoestrogens capable of binding the receptors for the natural hormone estradiol-17ß (E2). To better understand how (xeno-)estrogens can affect the skeleton in fish species with high ecological and commercial interest, 16 days post-hatch larvae of the seabass were experimentally exposed for 7 days to E2 and Bisphenol A (BPA), both used at the regulatory concentration of surface water quality (E2: 0.4 ng.L-1, BPA: 1.6 µg.L-1) or at a concentration 100 times higher. Skeletal mineralization levels were evaluated using Alizarin red staining, and expression of several genes playing key roles in growth, skeletogenesis and estrogen signaling pathways was assessed by qPCR. Our results show that E2 exerts an overall negative effect on skeletal mineralization at the environmental concentration of 0.4 ng.L-1, correlated with an increase in the expression of genes associated only with osteoblast bone cells. Both BPA exposures inhibited mineralization with less severe effects and modified bone homeostasis by regulating the expression of gene encoding osteoblasts and osteoclasts markers. Our results demonstrate that environmental E2 exposure inhibits larval growth and has an additional inhibitory effect on skeleton mineralization while both BPA exposures have marginal inhibitory effect on skeletal mineralization. All exposures have significant effects on transcriptional levels of genes involved in the skeletal development of seabass larvae.