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This study aimed at determining whether in vitro secretion of two neuropeptides, arginine vasotocin (AVT) and isotocin (IT), from pituitary cells of gilthead sea bream Sparus aurata was affected by cortisol and urotensin (UI). Pituitary cells were exposed to 1·4 × 10(-8) , 1·4 × 10(-7) and 0·4 × 10(-6)  M cortisol and 10(-12) , 10(-10) and 10(-8)  M UI for 6, 24 and 48 h, respectively. AVT and IT contents were determined in the culture media by high-performance liquid chromatography (HPLC). An increase in AVT secretion and a decrease in IT secretion were observed at all cortisol doses. UI increased AVT secretion after 6 h of incubation at all doses. After 24 h, however, only the highest dose of UI still displayed an effect. IT secretion was not influenced by UI. It was thus demonstrated that cortisol does influence AVT and IT secretion from S. aurata pituitary cells, while UI regulates AVT secretion, as a component of hypothalamic-pituitary-interrenal (HPI) axis in this species.

Various master key regulators (MKRs) that control a binary switch of sex determination (SD) have been found in fish; these provide an excellent model for the study of vertebrate genetic SD. The SD region in flathead grey mullet has been previously mapped to a 1 Mbp region harboring 27 genes, of which one is follicle-stimulating hormone receptor (fshr). Although this gene is involved in gonad differentiation and function, it has not been considered as an MKR of SD. We systematically investigated polymorphism in mullet fshr using DNA shotgun sequences, and compared them between males and females. Capable of encoding nonconservative amino acid substitutions, c.1732G>A and c.1759T>G exhibited association with sex on a population level (N = 83; P ≤ 6.7 × 10−19). Hence, 1732 A and 1759 G represent a male-specific haplotype of the gene, designated as “fshry.” Additional flanking SNPs showed a weaker degree of association with sex, delimiting the SD critical region to 143 nucleotides on exon 14. Lack of homozygotes for fshry, and the resulting divergence from Hardy–Weinberg equilibrium (N = 170; P ≤ 3.9 × 10−5), were compatible with a male heterogametic model (XY/XX). Capable of replacing a phenylalanine with valine, c.1759T>G alters a conserved position across the sixth transmembrane domain of vertebrate FSHRs. Amino acid substitutions in this position in vertebrates are frequently associated with constant receptor activation and consequently with FSH/FSHR signaling alteration; thus, indicating a potential role of fshr as an MKR of SD.

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23A study comprised of two trials was carried out to determine and compare the effects of water 24 turbidity produced by live microalgae and inert clay particles on the larval rearing of grey mullet 25 (Mugil cephalus). ITrial 1 evaluated the effect water turbidity generated by microalgae on grey mullet 26 larval performance and digestive enzyme activities along ontogeny. In particular, two microalgae 27 (Nannochloropsis oculata and Isochrysis. galbana) were used, whereas water turbidity levels (0.76 28 and 1.20 NTU) and a non-microalgae control (0.26 NTU) were tested from 2 to 23 dph grey mullet 29 larvae (5 treatments). The higher turbidity (1.2 NTU) larvae (5 dph) consumed markedly (P < 0.05) 30 more rotifers than other treatment fish, independently of the microalgae type. Alkaline phosphatase 31 activity was ca. 8 times higher and α-amylase activity increased 5.3 times in 79 dph fish compared to 32 40 dph individuals. The ratio of alkaline phosphatase and leucine-alanine aminopeptidase indicated 33 gut maturation occurred around 61 dph, as well as a transition from carnivorous to omnivorous 34 feeding habits. Trial 2 compared the most effective N.occulata produced turbidity level (1.2 NTU) 35 with the identical water turbidity produced by inert clay on larval performance. M. cephalus larvae 36 exposed to high algal turbidity demonstrated superior performance (P < 0.05), in terms of rotifer 37 ingestion, dry weight gain and survival, in comparison to cohorts reared under the clay treatment as 38 well as a lower microalgae produced turbidity. These findings suggested that water algal turbidity is 39 not the dominant factor determining improved grey mullet larval performance. 40 41 (Papandroulakis et al., 2002; van der Meeren et al., 2007; Bentzon-Tilia et al., 2016). On the other 47 hand, it remains speculative how algal supplementation contributes to larval growth and survival or 48 whether this benefit is species-specific. The biochemical composition of algal species (e.g. fatty 49 acids) varies considerably and it is entirely possible that particular compounds secreted from the algal 50 cell (e.g. polysaccharides) and/or are released during digestion might stimulate the immune system 51 or enhance the digestive process in larvae (Hemaiswarya et al., 2011). In addition, water turbidity 52 from specific algal concentrations may modify the light milieu for larvae, providing optimal 53 backlighting for larvae to facilitate live prey identification (e.g. rotifers), foraging behavior and 54 thereby enhancing hunting success (Rocha et al., 2008). 55The grey mullet (Mugil cephalus) is an economically important euryhaline and eurythermal species 56 contributing to sizable fisheries of estuarine and coastal regions in a variety of countries. It has been 57 traditionally farmed extensively in ponds and enclosures in the Mediterranean region, South East 58 Asia, Korea, Taiwan, China, Japan and Hawaii (FAO, 2018) and has been recently recognized as a 59 highly valued candidate for more intensive aquaculture (Whitfield e...