Senegalese sole was one of the earliest identified candidate species with high potential for aquaculture diversification in the south of Europe. Its culture has been possible, and commercially attempted, for several decades, but intensive production has been slow to take off. This has been explained mostly by serious disease problems, high mortality at weaning, variable growth and poor juvenile quality. However, a strong and sustained research investment that started in the eighties has led to a better understanding of the requirements and particularities of this species. More recently, better management and technical improvements have been introduced, which have led to important progress in productivity and given a new impetus to the cultivation of Senegalese sole. As a result, the last 5 years have marked a probable turning point in the culture of sole towards the development of a knowledge-driven, competitive and sustainable industry. This review will focus on the main technical improvements and advances in the state of knowledge that have been made in the last decade in areas as diverse as reproductive biology, behaviour, physiology, nutritional requirements, modulation of the immune system in response to environmental parameters and stress, and characterization and mitigation of the main disease threats. It is now clear that Senegalese sole has important particularities that differentiate it from other current and candidate marine aquaculture species, which bring about important challenges, some still unsolved, but also notable opportunities (e.g. a nutritional physiology that is better adapted to dietary vegetable ingredients), as will be discussed here.

This article reviews the use of hormonal treatments to enhance sperm production in aquaculture fish and the methods available for evaluating sperm quality. The different types of testis development are examined and a brief review is presented of the endocrine regulation of spermatogenesis in fishes, including the increasing evidence of the existence of spermatozoa subpopulations. Hormonal manipulations are employed to induce spermatogenesis in species such as the freshwater eels, to synchronize maximal sperm volume to ovulation for in vitro fertilization and to enhance sperm production in species with poor spermiation. The hormones that are employed include gonadotropins (GtH) of piscine or mammalian origin, and gonadotropin-releasing hormone agonists (GnRHa) administered by injections or controlled-release delivery systems, with or without dopaminergic inhibitors. Pheromones in the culture water and hormones added to the sperm in vitro have also been employed to enhance spermiation and sperm quality, respectively, in some fishes. Hormonal therapies usually do not affect sperm quality parameters, except in cases where fish fail to spermiate naturally or produce very small volumes of high-density sperm. Different parameters have been used to evaluate fish sperm quality, including sperm volume and density, spermatozoa motility and morphometry, and seminal plasma composition. The development of Computer-Assisted Sperm Analysis (CASA) systems made possible the estimation of a higher number of sperm motion parameters using an objective, sensitive and accurate technique. The development of Assisted Sperm Morphology Analysis (ASMA) software has introduced a new approach for sperm evaluation studies, demonstrating changes in the spermatozoa related to reproductive season, hormonal treatments or the cryopreservation processes, and how these may be related to changes in sperm motility and fertilization capacity. The article concludes with a few practical protocols for the enhancement of sperm production in aquaculture species.

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The objective of the study was to acclimatise wild-caught meagre (Argyrosomus regius) to captivity to produce viable eggs for aquaculture production. Twelve meagre (3 males and 9 females, mean weight = 20 ± 7 kg) were caught and transported to a land-based facility on 26 October 2006. During, March to June 2007, all three males were spermiating and five of the nine females were in vitellogenesis with mean maximum oocyte diameter ≥550 μm. No spontaneous spawning was observed. Two hormone treatments, either a single injection of gonadotropin-releasing hormone agonist (GnRHa, 20 μg kg(-1) for females and 10 μg kg(-1) for males) or a slow-release implant loaded with the same GnRHa (50 μg kg(-1) for females and 25 μg kg(-1) for males), were used to induce spawning on three different dates on 26 March 2007, 4 May 2007 and 18 April 2008. From each spawning event, the following parameters were determined: fecundity, number of floating eggs, egg size, fertilisation and hatching success, unfed larval survival, and proximal composition and fatty acid profile of the eggs. In 2007, two females that were injected on 26 March and 4 May spawned a total of 5 times producing 9,019,300 floating eggs and a relative fecundity of 198,200 eggs kg(-1) and two different females that were implanted on the same dates spawned 14 times producing 12,430,000 floating eggs and a relative fecundity of 276,200 eggs kg(-1). In 2008, a pair that was implanted spawned five times producing a total of 10,211,900 floating eggs and a relative fecundity of 527,380 eggs kg(-1). The latency period was 48-72 h. Parameters were compared between hormone treatments, date of hormone induction and parents determined by microsatellites. Percentage hatch and egg size were 70 ± 0.3% and 0.99 ± 0.02 mm, respectively, for GnRHa-implanted fish and were significantly higher (P < 0.05) compared to 30 ± 0.3% and 0.95 ± 0.03 mm, respectively, for injected fish. Few differences were observed in proximal composition and fatty acid profile and for all spawns mean (% dry weight) lipid content was 17.3 ± 3.0%, carbohydrate was 4.4 ± 1.9% and protein was 31.5 ± 6.4% and the essential fatty acids: Arachidonic acid (ARA, 20:4n-6) ranged between 0.9 and 1% (of total fatty acids), eicosapentaenoic acid (EPA 20:5n-3) 7.7-10.4% and docosahexaenoic acid (DHA 22:6n-3), 28.6-35.4%. All good quality spawns were obtained in the second and/or third spawn after GnRHa treatment, whereas all bad quality spawns were obtained either on the first spawn or after the fifth spawn. Both spawning protocols gave commercially viable (1,000,000+) numbers of good quality eggs that could form the basis of a hatchery production.

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