Aquaculture 

About: Aquaculture is an academic journal. The journal publishes majorly in the area(s): Shrimp & Fish meal. It has an ISSN identifier of 0044-8486. Over the lifetime, 19564 publication(s) have been published receiving 776244 citation(s).

Sex determination and sex differentiation in fish: an overview of genetic, physiological, and environmental influences

Abstract: A great deal of information is known regarding the process of sex differentiation in fish, and the mechanisms involved in primary sex determination are now beginning to be defined. A range of gonadal differentiation types have been described for fish, including gonochoristic species possessing purely ovarian or testicular tissues, as well as hermaphroditic species that can initially mature either as males (protandrous) or females (protogynous). Sex determination in fish is a very flexible process with respect to evolutionary patterns observed among genera and families, and within individuals is subject to modification by external factors. These influences can affect the fate of both somatic and germ cells within the primordial gonad, and include the action of genetic, environmental (e.g. temperature), behavioural, and physiological factors. Exogenous sex steroids administered at the time of sex determination can strongly influence the course of sex differentiation in fish, suggesting that they play a critical role in assignment of gonad determination as well as subsequent differentiation. Detailed information is available from fish systems describing the production of sex steroids, as well as the enzymes involved in steroid production. Both estradiol and the maturation hormone 17α, 20β-dihydroxy-4-pregnen-3-one (17α, 20β-DP) are produced by a two-step process involving different cell layers in the gonad, and have effects on the differentiation of gonadal and nongonadal tissues. Gonadal development and differentiation in some fish is also controlled by hormones from the pituitary gland (gonadotropins) that are regulated by release hormones (GnRH) and other neuroendocrine and gonadal factors. Genetic determination of sex in fish can involve monogenic or polygenic systems, with factors located on the autosomes or on sex chromosomes. In the latter case, both male (XY) and female (ZW) heterogametic systems have been described, as well as many subtle variations on these themes. Sex chromosomes are found in approximately 10% of fish species examined, and sex-linked phenotypic traits, and protein and molecular genetic markers have been identified in several fish systems. Some species of fish reproduce gynogenetically, producing all-female populations. Several gene families known to be involved in sex determination in other vertebrates have recently been shown to be similarly involved in fish, suggesting conservation of sex determination pathways. The lability of sex-determination systems in fish makes some species sensitive to environmental pollutants capable of mimicking or disrupting sex hormone actions. Such observations provide important insight into potential impacts from endocrine disruptors, and can provide useful monitoring tools for impacts on aquatic environments.

Antinutritional factors present in plant-derived alternate fish feed ingredients and their effects in fish

Abstract: The use of plant-derived materials such as legume seeds, different types of oilseed cake, leaf meals, leaf protein concentrates, and root tuber meals as fish feed ingredients is limited by the presence of a wide variety of antinutritional substances. Important among these are protease inhibitors, phytates, glucosinolates, saponins tannins, lectins, oligosaccharides and non-starch polysaccharides, phytoestrogens, alkaloids, antigenic compounds, gossypols, cyanogens, mimosine, cyclopropenoid fatty acids, canavanine, antivitamins, and phorbol esters. The effects of these substances on finfish are reviewed. Evidently, little unanimity exists between the results of different studies as to the specific effects of antinutrients, since most studies have been conducted using an ingredient rich in one particular factor and the observed effects have been attributed to this factor without considering other antinutrients present in the ingredient, or interactions between them. Tentatively, protease inhibitors, phytates, antigenic compounds, and alkaloids, at levels usually present in fish diets containing commercially available plant-derived protein sources, are unlikely to affect fish growth performance. In contrast, glucosinolates, saponins, tannins, soluble non-starch polysaccharides, gossypol, and phorbol esters, are more important from a practical point of view. The effectiveness of common processing techniques such as dry and wet heating, solvent extraction and enzyme treatment in removing the deleterious effects of antinutrients from feed materials is discussed. More insights into the nutritional, physiological and ecological effects of antinutrients on fish need to be accumulated through studies using purified individual antinutrients and their mixtures in proportions similar to those in alternative nutritional sources in fish feeds. Such studies would provide data useful for designing optimum inclusion levels of plant-derived materials and treatment methods that would neutralise the negative effects of the antinutritional factors.

Global overview on the use of fish meal and fish oil in industrially compounded aquafeeds: Trends and future prospects

Abstract: article i nfo The finfish and crustacean aquaculture sector is still highly dependent upon marine capture fisheries for sourcing key dietary nutrient inputs, including fish meal and fish oil. This dependency is particularly strong within compound aquafeeds for farmed carnivorous finfish species and marine shrimp. Results are presented concerning the responses received from a global survey conducted between December 2006 and October 2007 concerning the use of fish meal and fish oil within compound aquafeeds using a questionnaire sent to over 800 feed manufacturers, farmers, researchers, fishery specialists, and other stakeholders in over 50 countries. On the basis of the responses received, it is estimated that in 2006 the aquaculture sector consumed 3724 thousand tonnes of fish meal (68.2% total global fish meal production in 2006) and 835 thousand tonnes of fish oil (88.5% total reported fish oil production in 2006), or the equivalent of 16.6 million tonnes of small pelagic forage fish (using a wet fish to fish meal processing yield of 22.5% and wet fish to fish oil processing yield of 5%) with an overall fish-in fish-out ratio of 0.70. At a species-group level, calculation of small pelagic forage fish input per unit of farmed fish or crustacean output showed steadily decreasing fish-in fish-out ratios for all cultivated species from 1995 to 2006, with decreases being most dramatic for carnivorous fish species such as salmon (decreasing from 7.5 to 4.9 from 1995 to 2006), trout (decreasing from 6.0 to 3.4), eel (decreasing from 5.2 to 3.5), marine fish (decreasing from 3.0 to 2.2) and to a lesser extent shrimp (decreasing by 1.9 to 1.4 from 1995 to 2006. Net fish producing species in 2006 (with fish-in fish-out ratios below 1), included herbivorous and omnivorous finfish and crustacean species, including non-filter feeding Chinese carp (0.2), milkfish (0.2), tilapia (0.4), catfish (0.5), and freshwater crustaceans (0.6).

Current research status of fish immunostimulants

Abstract: Immunostimulants are valuable for the control of fish diseases and may be useful in fish culture. The immunostimulatory effects of glucan, chitin, lactoferrin and levamisole for fish and shrimp have been reported. Nutritional factors such as Vitamins B and C, growth hormone and prolactin have also been reported to be immunostimulators. These immunostimulants mainly facilitate the function of phagocytic cells and increase their bactericidal activities. Several immunostimulants also stimulate the natural killer cells, complement, lysozyme and antibody responses of fish. The activation of these immunological functions is associated with increased protection against infectious disease. Resistance to bacterial pathogens such as Vibrio anguillarum, V. salmonicida, Aeromonas salmonicida, Yersinia rukeri and Streptococcus spp. and to parasitic infections such as white spot disease can be increased by administration of immunostimulants, but not to intracellular pathogens such as Renibacterium salmoninarum and Pasteurella piscicida. The most effective method of administration of immunostimulants to fish is by injection. Oral and immersion methods have also been reported, but the efficacy of these methods decreases with long-term administration. Overdoses of several immunostimulants induce immunosuppression in fish. The side effects of immunostimulants have not been well-studied. Growth-promoting activity has been noted in fish or shrimp treated with glucan or lactoferrin. Immunostimulants can overcome immune suppression by sex hormones. Thus, the influence of immunostimulants in mature fish should be studied. In conclusion, immunostimulants can reduce the losses caused by disease in aquaculture; however, they may not be effective against all diseases. For the effective use of immunostimulants, the timing, dosages, method of administration and the physiological condition of fish need to be taken into consideration.

The use of probiotics in aquaculture

Abstract: The research of probiotics for aquatic animals is increasing with the demand for environment-friendly aquaculture. The probiotics were defined as live microbial feed supplements that improve health of man and terrestrial livestock. The gastrointestinal microbiota of fish and shellfish are peculiarly dependent on the external environment, due to the water flow passing through the digestive tract. Most bacterial cells are transient in the gut, with continuous intrusion of microbes coming from water and food. Some commercial products are referred to as probiotics, though they were designed to treat the rearing medium, not to supplement the diet. This extension of the probiotic concept is pertinent when the administered microbes survive in the gastrointestinal tract. Otherwise, more general terms are suggested, like biocontrol when the treatment is antagonistic to pathogens, or bioremediation when water quality is improved. However, the first probiotics tested in fish were commercial preparations devised for land animals. Though some effects were observed with such preparations, the survival of these bacteria was uncertain in aquatic environment. Most attempts to propose probiotics have been undertaken by isolating and selecting strains from aquatic environment. These microbes were Vibrionaceae, pseudomonads, lactic acid bacteria, Bacillus spp. and yeasts. Three main characteristics have been searched in microbes as candidates to improve the health of their host. (1) The antagonism to pathogens was shown in vitro in most cases. (2) The colonization potential of some candidate probionts was also studied. (3) Challenge tests confirmed that some strains could increase the resistance to disease of their host. Many other beneficial effects may be expected from probiotics, e.g., competition with pathogens for nutrients or for adhesion sites, and stimulation of the immune system. The most promising prospects are sketched out, but considerable efforts of research will be necessary to develop the applications to aquaculture.