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Microalgae are increasingly being studied to replace fishmeal in aquafeed production. Low level Spirulina supplementation to various fish species has been widely investigated, demonstrating enhanced growth and better product quality. In order to evaluate the effects of a full fishmeal replacement with Spirulina (Arthrospira platensis) on growth and product quality in African catfish (Clarias gariepinus), two isoenergetic diets were formulated and fed for ten weeks to 120 fish with an average initial weight of 50 ± 3 g. Full supplementation of Spirulina resulted in reduced growth (p &lt, 0.001) whereas feed conversion ratio was on par (p &gt, 0.05). Furthermore, Spirulina-fed fish showed a more intense yellow coloration in skin, and raw and cooked fillet (p &lt, 0.001). The analysis of fatty acids revealed higher proportions of C16:0 (p &lt, 0.001) and C18:2n6 (p &lt, 0.05) in fish fed the Spirulina-diet while C24:0 (p &lt, 0.01) and C20:5n3 (p &lt, 0.001) were found to be higher in the control group. Even though no statistically significant differences in the overall SFA, MUFA and PUFA were detected, a slight increase of the n6/n3 ratio was observed in the Spirulina-fed fish. Without further optimization of the feed ration, a complete fishmeal replacement with Spirulina can lead to economic losses. It remains to be studied whether the observed changes in product quality affect consumer acceptance.

Background In Nile tilapia sex determination is governed by a male heterogametic system XX/XY either on LG1 or LG23. The latter carries a Y-specific duplicate of the amh gene, which is a testis-determining factor. Allelic variants in the amh gene demonstrated to be major triggers for autosomal and temperature-dependent sex reversal. Further, QTL on LG23 and LG20 show a temperature-responsiveness with influence on the phenotypic sex relative to the sex chromosomes. Here we present a ddRADseq based approach to identify genomic regions that show unusual large differentiation in terms of fixation index (FST) between temperature-treated pseudomales and non-masculinized females using a comparative genome-scan. Genome-wide associations were identified for the temperature-dependent sex using a genetically all-female population devoid of amh-ΔY. Results Twenty-two thousand three hundred ninety-two SNPs were interrogated for the comparison of temperature-treated pseudomales and females, which revealed the largest differentiation on LG23. Outlier FST-values (0.35–0.44) were determined for six SNPs in the genomic interval (9,190,077–11,065,693) harbouring the amh gene (9,602,693–9,605,808), exceeding the genome-wide low FST of 0.013. Association analysis with a set of 9104 selected SNPs confirmed that the same genomic region on LG23 exerts a significant effect on the temperature-dependent sex. Conclusions This study highlights the role of LG23 in sex determination, harbouring major determinants for temperature-dependent sex reversal in Nile tilapia. Furthermore FST outlier detection proves a powerful tool for detection of sex-determining regions in fish genomes. Electronic supplementary material The online version of this article (doi:10.1186/s12864-017-3930-0) contains supplementary material, which is available to authorized users.

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. Nonsex-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.

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

This study investigated the effects of stocking density and photoperiod manipulation in relation to plasma estradiol-17? (E2) profile to enhance spawning activity in female Nile tilapia (Oreochromis niloticus) using F1 clonal crosses. The fish were divided into experimental and control groups and subjected to a combination of stocking density and photoperiod treatments (40kg/m3;6L:18D, 40kg/m3;12L:12D and transferred into single compartments at 12L:12D; 14kg/m3;12L:12D), respectively. Blood samples were taken by caudal puncture from experimental fish for estradiol profile analysis. Results showed that experimental fish exhibited significantly higher number of spawns per day, total fecundity and relative fecundity (p

Sex in the Nile tilapia, Oreochromis niloticus, is governed by the interactions between a complex genetic sex determination system and the influence of temperature. High temperatures applied during a critical period of sex differentiation can induce masculinisation in some progenies originating from both domestic and wild stocks. Differences in thermo-sensitivity were observed between the wild populations and both paternal and maternal effects have been demonstrated, suggesting that it is a heritable trait. This has been confirmed by the development of divergent lines for thermo-sensitivity. Two thermo-sensitive divergent lines were selected with regard to their sex ratios showing high (=90% males) and low responses (only 54%) when treated at 36°C temperatures. At least one of the mechanisms by which temperature exerts its effects on sex differentiation is through a downregulation of aromatase Cyp19. Expression profiles were analysed in monosex XX populations treated at 27°C and 36°C temperatures showing that temperature up-regulates Sox9s, Amh, IGFs, Dax1 and down-regulates other genes such as aromatase Cyp19-1a. Variation in these gene expression levels was associated with the percentage of males obtained by temperature treatments. The divergent thermo-sensitive lines have been used to complement our study done on the monosex populations. Expression of Cyp19-1a was also analysed in these two divergent lines. (Texte intégral)