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Disease and parasitism cause major welfare, environmental and economic concerns for global aquaculture. In this review, we examine the status and potential of technologies that exploit genetic variation in host resistance to tackle this problem. We argue that there is an urgent need to improve understanding of the genetic mechanisms involved, leading to the development of tools that can be applied to boost host resistance and reduce the disease burden. We draw on two pressing global disease problems as case studies—sea lice infestations in salmonids and white spot syndrome in shrimp. We review how the latest genetic technologies can be capitalised upon to determine the mechanisms underlying inter‐ and intra‐species variation in pathogen/parasite resistance, and how the derived knowledge could be applied to boost disease resistance using selective breeding, gene editing and/or with targeted feed treatments and vaccines. Gene editing brings novel opportunities, but also implementation and dissemination challenges, and necessitates new protocols to integrate the technology into aquaculture breeding programmes. There is also an ongoing need to minimise risks of disease agents evolving to overcome genetic improvements to host resistance, and insights from epidemiological and evolutionary models of pathogen infestation in wild and cultured host populations are explored. Ethical issues around the different approaches for achieving genetic resistance are discussed. Application of genetic technologies and approaches has potential to improve fundamental knowledge of mechanisms affecting genetic resistance and provide effective pathways for implementation that could lead to more resistant aquaculture stocks, transforming global aquaculture. [ABSTRACT FROM AUTHOR]

Sexual maturation and gonadal development of fish is greatly influenced by photic information, an external environmental factor, and melatonin mediates this information to regulate gonadotropin (GTH) secretion and gonadal activation. The relationship between gonadotropin inhibiting hormone (GnIH) and melatonin in fish, however, has not been studied to date. Here, the GnIH expression pattern and daily change of melatonin levels were compared to each other in mature tilapia (body length 16.1 ± 0.2 cm, body weight 77.7 ± 3.43 g), and the effect of melatonin injection on GnIH gene expression was investigated. GnIH gene expression increased at night when the secretion of melatonin increased, whereas gene expression decreased during the day when melatonin secretion decreased. Injecting tilapia intraperitoneally with melatonin increased GnIH gene expression and decreased the expression of gonadotropin releasing hormone (GnRH) and GTH. Furthermore, the injection decreased the 11-KT concentration in male tilapia. These results indicate that melatonin is likely to suppress the hypothalamus-pituitary-gonad (HPG) axis via the action of GnIH in this species. [ABSTRACT FROM PUBLISHER]

It has been suggested that kisspeptin influences reproduction and onset of puberty in fishes. Unlike mammals, which produce only one kisspeptin (Kiss1), some teleosts have two, Kiss1 and Kiss2, both thought to be involved in the stimulation of gonadotropin (GTH) secretion. In Nile tilapia ( Oreochromis niloticus ), however, only Kiss2 has been identified so far. The effect of Kiss2 on GTH release varies significantly depending on species and reproductive stage. Furthermore, its physiological function in this species is not clearly defined. In this study, kiss2 gene expression profiles were examined using quantitative real-time PCR (qRT-PCR) in the brain, pituitary, and gonads of Nile tilapia at different reproductive stages (male: immature, pre-spermiation, post-spermiation; female: immature, pre-spawning, post-spawning). The kiss2 mRNA expression profiles of the brain, pituitary, and gonads of both sexes shared a similar pattern their expression was significantly higher at the immature stage than at the mature or post-spawning stages, implying it is involved in early gonadal maturation in this species. To investigate the effect of kisspeptin on the hypothalamus-pituitary-gonad (HPG) axis in vivo, synthetic kisspeptin2 (FNYNPLSLRF) was injected into immature male and female tilapia intraperitoneally (i.p.) at a dose of 200 pmol/g body weight. The results showed that synthetic Kiss2 administration increased the expression of GnRH I , fshβ and lhβ mRNA in the brain and increased 17 β -estradiol (E 2 ) and 11-ketotestosterone (11-KT) levels in the plasma. These results suggest that Kiss 2 stimulates the expression of GnRH and GTH genes in immature Nile tilapia. [ABSTRACT FROM AUTHOR]