Current Aquaculture Practices Research Articles

Plasma cortisol and production of miRNAs in red drum (Sciaenops ocellatus) exposed to three distinct challenges.

The red drum Sciaenops ocellatus is a marine fish species of high commercial interest. Despite improvements in current aquaculture practices, there are still concerns about the impact of daily manipulations regarding fish welfare. To investigate how does fish respond to various challenges, S. ocellatus juveniles were submitted to two acute challenges, namely a confinement stress and a cold-temperature shock, as well as a chronic stress challenge consisting of 18days of repetitive challenge events. The level of cortisol produced by individuals was used as a measure of activation hypothalamic-pituitary-interrenal (HPI) axis. A significant increase in cortisol levels was detected only after the confinement stress. Interestingly, the fish exposed to a chronic stress for 18days exhibited cortisol levels significantly lower than those of non-challenged fish. The small RNA-sequencing conducted for the chronic stress experiment only allowed us to identify two plasmatic microRNAs more abundant in non-challenged fish (miR-205-1-5p and let-7b-5p) compared to challenged fish. The miR-205-1-5p was of particular interest since it was already detected in previous studies on other fish species. In silico analysis allowed to predict potentially highly conserved mRNA targets of this specific miRNA, among which is tnfrsfa that plays a key role in the secondary stress response.

Cultivation of Brook Charr Salvelinus fontinalis: The Challenges of Disease Control and the Promise of Microbial Ecology Management

Among salmonids, brook charr, Salvelinus fontinalis has been gaining popularity in aquaculture. However, major limitations associated with opportunistic diseases that result from unstable egg and fry‐rearing conditions are experienced under intensive rearing conditions. Great losses in brook charr culture result from viral (e.g., infectious pancreatic necrosis, viral hemorrhagic septicemia virus), fungal (e.g., saprolegniosis), and bacterial (e.g., furunculosis, cold water disease, columnaris) diseases. Unfortunately, there is no effective treatment for viral diseases for brook charr, and the chemical disinfectants and antibiotics commonly used against bacterial and fungal infections are reaching their limits (pathogen resistance, microbial community disruption), making alternative and more sustainable rearing approaches essential to bolster aquaculture. In this regard, recent studies show that many microbial species (bacteria, archaea, viruses, eukaryotes‐like protozoa, and unicellular fungi) are essential from the earliest life stages for the proper development and growth of fish. Based on ecological theory and work on marine fish, it has been hypothesized that current aquaculture practices favor r‐strategic, opportunistic microbes that are detrimental to fish health and development. Consequently, to ensure the success and sustainability of brook charr farming, a new aquaculture paradigm involving recirculating aquaculture systems (RAS) that select a K‐enriched, specialized microbial community as a preventive measure against those microbial diseases is a very promising avenue. In this review, after introducing brook charr biology, the role of microbes in brook charr rearing and the general problems of disease and low fry survival due to an imbalance in the microbial community will be discussed. Various curative and prophylactic treatment methods currently used to control these diseases and their impact on microbial ecology will be covered, and we will conclude with the rationale of microbial ecology management and its effectiveness in promoting fry survival through disease prevention. To our knowledge, this is the first literature review addressing the promises of managing microbial ecology in a sustainable way in the brook char industry.

Biological life‐history and farming scenarios of marine aquaculture to help reduce wild marine fishing pressure

AbstractAquaculture (freshwater and marine) has largely supplemented fisheries, but in theory could help reduce fishing pressure on wild stocks. Although not the sole factors, some potential benefits depend on aquaculture pressures on fished species, including collection of wild ‘seed’ material—earlier to later life stages—for rearing in captivity and the capacity of aquaculture to increase. Here we first classify 203 marine (saltwater and brackish) animal species as being produced by either open‐cycle capture‐based aquaculture (CBA) or closed‐cycle domesticated aquaculture (DA)—based on their likely reliance on wild seed—and assess the extent to which these forms of aquaculture could support seafood production and greater wild biomass. Using a data‐limited modelling approach, we find evidence that current aquaculture practices are not necessarily helping reduce fishing to sustainable levels for their wild counterparts—consistent with emerging scientific research. However, if some wild capture species (87 equivalent spp.) were instead produced through CBA, almost a million extra tonnes could theoretically be left in the wild, without reducing seafood production. Alternatively, if reliance on wild seed inputs is further reduced by shifting to DA production, then a little less than doubling of aquaculture of the overexploited species in our study could help fill the ‘production gap’ to support fishing at maximum sustainable levels. While other ecological (e.g. escapes), social and economic considerations (e.g. market substitution) are important, we focused on a critical biological linkage between wild fisheries and aquaculture that provides another aspect on how to improve management alignment of the sectors.

Xenosteroids in aquaculture with special consideration to Lake Manzala (Northern delta lake, Egypt): Types, sources and mechanism of action

Egyptian aquaculture production has dramatically increased in recent years and is anticipated to represent a yield of 1.8MMT in 2018. Increased demand for fish production has led to a higher intensification of aquaculture to face these challenges. However, the current aquaculture practices and restricted governmental legislation can prompt raised concerns about aquaculture pollution. The current review summarizes our knowledge concerning general Egyptian aquaculture, legislation and practices that can lead to persistent pollutant exposure in farmed finfish. Xenosteroids are critical pollutants influencing fish health, as detailed in this review, and are considered significant health hazards not only to cultured fish but also to human wellbeing, raising a public health concern. Additional research studies are warranted to better understand their public health concerns and develop strategic plans and policies to prevent these impacts and maintain fish welfare and aquaculture sustainability.

Menthol essential oil is a practical choice for intensifying the production of Nile tilapia (Oreochromis niloticus): Effects on the growth and health performances

Increasing the stocking density of aquatic organisms becomes an urgent procedure in the current aquaculture practices. Concurrently, this study investigated the possibility of growing Nile tilapia under high stocking density while fortifying their feed with menthol essential oil (EO). Fish with the initial average weight of 17.19 ± 0.051 g/fish were allotted in eighteen tanks (80-L), representing six groups. The first and fourth groups stocked with 10 fish/tank (low density, LD), the second and fifth groups stocked with 20 fish/tank (medium density, MD), and the third and sixth groups stocked with 30 fish/tank (high density, HD). The first three groups received the basal diet without menthol EO, while the remaining groups received a menthol EO mixed diet. The values of water total ammonia nitrogen (TAN), ammonia‑nitrogen (NH3−N), and ammonium‑nitrogen (NH4+-N) increased in the HD group, followed by MD, and the lowest levels were seen in the LD group either with or without dietary menthol EO. There is a marked effect of stocking density and menthol EO on the final weight, weight gain, specific growth rate traits, and feed efficiency ratio (p < 0.05). Further, the stocking density and menthol EO were significant factors (p < 0.05) on the serum triglycerides, alanine aminotransferase, aspartate aminotransferase, total protein, albumin, globulin, uric acid, urea, and creatinine levels. The cortisol levels were markedly (p < 0.05) increased in fish fed the basal diet and reared in HD but decreased in fish fed menthol EO and grown in LD and MD conditions. Nevertheless, the glucose level is sharply increased with increasing the stocking density in a linear trend (p < 0.05). The antioxidative-related factors (SOD, CAT, and GPx) were markedly impacted by menthol EO and stocking density and showed the highest activities by menthol EO. The histological study showed inflammatory features in the gills and liver of fish under HD conditions, while dietary menthol EO relieved the inflammation induced by high malonaldehyde concentration. Altogether, dietary menthol EO resulted in enhanced growth rate, health status, and antioxidative capacity in LD, MD, and HD conditions, referring to high immune status and well-being of Nile tilapia.

Identifying Drivers of Genetically Modified Seafood Demand: Evidence from a Choice Experiment

The aquaculture industry has expanded to fill the gap between plateauing wild seafood supply and growing consumer seafood demand. The use of genetic modification (GM) technology has been proposed to address sustainability concerns associated with current aquaculture practices, but GM seafood has proved controversial among both industry stakeholders and producers, especially with forthcoming GM disclosure requirements for food products in the United States. We conduct a choice experiment eliciting willingness-to-pay for salmon fillets with varying characteristics, including GM technology and GM feed. We then develop a predictive model of consumer choice using LASSO (least absolute shrinkage and selection operator)-regularization applied to a mixed logit, incorporating risk perception, ambiguity preference, and other behavioral measures as potential predictors. Our findings show that health and environmental risk perceptions, confidence and concern about potential health and environmental risks, subjective knowledge, and ambiguity aversion in the domain of GM foods are all significant predictors of salmon fillet choice. These results have important implications for marketing of foods utilizing novel food technologies. In particular, people familiar with GM technology are more likely to be open to consuming GM seafood or GM-fed seafood, and effective information interventions for consumers will include details about health and environmental risks associated with GM seafood.

Swimming exercise to control precocious maturation in male seabass (Dicentrarchus labrax)

BackgroundMale European seabass, already predominant (~ 70%) in cultured stocks, show a high incidence (20–30%) of precocious sexual maturation under current aquaculture practices, leading to important economic losses for the industry. In view of the known modulation of reproductive development by swimming exercise in other teleost species, we aimed at investigating the effects of sustained swimming on reproductive development in seabass males during the first year of life in order to determine if swimming could potentially reduce precocious sexual maturation.MethodsPre-pubertal seabass (3.91 ± 0.22 g of body weight (BW)) were subjected to a 10 week swimming regime at their optimal swimming speed (Uopt) in an oval-shaped Brett-type flume or kept at rest during this period. Using Blazka-type swim tunnels, Uopt was determined three times during the course of the experiment: 0.66 m s− 1 at 19 ± 1 g BW, 10.2 ± 0.2 cm of standard length (SL) (week 1); 0.69 m s− 1 at 38 ± 3 g BW, 12.7 ± 0.3 cm SL (week 5), and also 0.69 m s− 1 at 77 ± 7 g BW, 15.7 ± 0.5 cm SL (week 9). Every 2 weeks, size and gonadal weight were monitored in the exercised (N = 15) and non-exercised fish (N = 15). After 10 weeks, exercised and non-exercised males were sampled to determine plasma 11-ketotestosterone levels, testicular mRNA expression levels of genes involved in steroidogenesis and gametogenesis by qPCR, as well as the relative abundance of germ cells representing the different spermatogenic stages by histological examination.ResultsOur results indicate that sustained swimming exercise at Uopt delays testicular development in male European seabass as evidenced by decreased gonado-somatic index, slower progression of testicular development and by reduced mRNA expression levels of follicle stimulating hormone receptor (fshR), 3-beta-hydroxysteroid dehydrogenase (3βhsd), 11-beta hydroxysteroid dehydrogenase (11βhsd), estrogen receptor-beta (erβ2), anti-mullerian hormone (amh), structural maintenance of chromosomes protein 1B (smc1β), inhibin beta A (inhba) and gonado-somal derived factor 1 (gsdf1) in exercised males as compared with the non-exercised males.ConclusionsSwimming exercise may represent a natural and non-invasive tool to reduce the incidence of sexually precocious males in seabass aquaculture.

Colorful invasion in permissive Neotropical ecosystems: establishment of ornamental non-native poeciliids of the genera Poecilia/Xiphophorus (Cyprinodontiformes: Poeciliidae) and management alternatives

ABSTRACT Headwater creeks are environments susceptible to invasion by non-native fishes. We evaluated the reproduction of 22 populations of the non-native livebearers guppy Poecilia reticulata, black molly Poecilia sphenops, Yucatan molly Poecilia velifera, green swordtail Xiphophorus hellerii, southern platyfish Xiphophorus maculatus, and variable platyfish Xiphophorus variatus during an annual cycle in five headwater creeks located in the largest South American ornamental aquaculture center, Paraíba do Sul River basin, southeastern Brazil. With few exceptions, females of most species were found reproducing (stages 2, 3, 4) all year round in the creeks and gravid females of all species showed small sizes indicating stunting. Juveniles were frequent in all sites. The fecundity of the six poeciliids was always low in all periods. The sex ratio was biased for females in most species, both bimonthly as for the whole period. Water temperature, water level and rainfall were not significantly correlated with reproduction in any species. Therefore, most populations appeared well established. The pertinence of different management actions, such as devices to prevent fish escape, eradication with rotenone and research about negative effects on native species, is discussed in the light of current aquaculture practices in the region.

Modelling the nitrogen loadings from large yellow croaker (Larimichthys crocea) cage aquaculture.

Large yellow croaker (LYC) cage farming is a rapidly developing industry in the coastal areas of the East China Sea. However, little is known about the environmental nutrient loadings resulting from the current aquaculture practices for this species. In this study, a nitrogenous waste model was developed for LYC based on thermal growth and bioenergetic theories. The growth model produced a good fit with the measured data of the growth trajectory of the fish. The total, dissolved and particulate nitrogen outputs were estimated to be 133, 51 and 82kgNtonne(-1) of fish production, respectively, with daily dissolved and particulate nitrogen outputs varying from 69 to 104 and 106 to 181mgNfish(-1), respectively, during the 2012 operational cycle. Greater than 80% of the nitrogen input from feed was predicted to be lost to the environment, resulting in low nitrogen retention (<20%) in the fish tissues. Ammonia contributed the greatest proportion (>85%) of the dissolved nitrogen generated from cage farming. This nitrogen loading assessment model is the first to address nitrogenous output from LYC farming and could be a valuable tool to examine the effects of management and feeding practices on waste from cage farming. The application of this model could help improve the scientific understanding of offshore fish farming systems. Furthermore, the model predicts that a 63% reduction in nitrogenous waste production could be achieved by switching from the use of trash fish for feed to the use of pelleted feed.

Climate Change, Effects and Mitigation Strategies on Aquaculture: A Review

This paper review and addresses the major effects of climate change on Aquaculture, whose contributions to agriculture development are quite enormous. To achieve these objectives the status of this sub sector to the total fish supply are therefore analyzed with a view to identifying the major impacts of climate change on aquaculture. Aquaculture not practiced evenly across the globe requires an evaluation of the effects of climate change through the current aquaculture practices in the regions and the different environments. The main elements of climate change that would impact on aquaculture production include sea level and temperature rise, change in monsoon patterns and extreme climatic events and water stress, among others thereby causing varying degrees of concern either positively or negatively or directly or indirectly. Therefore, to ameliorate this adverse effect of climate change on aquaculture in Nigeria, and the world generally, attempts are made to deal with the climate change effects on the different culture systems in order to bring out all the complex attributes of climate change and the possible mitigation strategies for the future control. These will enhance aquaculture production and then claim back the expected role as a major source of animal protein in the future.

Deep insight into white spot syndrome virus vaccines: A review

White spot syndrome virus (WSSV), the causative virus of the disease, is found in most shrimp farming areas of the world, where it causes large economic losses to the shrimp farming industry. The potentially fatal virus has been found to be a threat not only to all shrimp species, but also to other marine and freshwater crustaceans, such as crab and crayfish. To date, no effective prophylactic treatment measures are available for viral infections in shrimp and other crustaceans. Due to current aquaculture practices and the broad host range of WSSV, intervention strategies including vaccination against this virus would be pivotal to save and protect shrimp farming. Several achievements have been attained in the search of novel vaccines for WSSV. DNA vaccination, recombinant vaccines, oral vaccination techniques and gene therapy are some of the thrust areas of focus for scientists and researchers. This review article highlights the recent trends in the development of WSSV vaccines either as DNA vaccines or recombinant vaccines and their functioning strategies as suggested by the researchers worldwide.

Finfish Aquaculture: Animal Welfare, the Environment, and Ethical Implications

The aim of this review is to assess the ethical implications of finfish aquaculture, regarding fish welfare and environmental aspects. The finfish aquaculture industry has grown substantially the last decades, both as a result of the over-fishing of wild fish populations, and because of the increasing consumer demand for fish meat. As the industry is growing, a significant amount of research on the subject is being conducted, monitoring the effects of aquaculture on the environment and on animal welfare. The areas of concern when it comes to animal welfare have here been divided into four different stages: breeding period; growth period; capturing and handling; and slaughter. Besides these stages, this report includes a chapter on the current evidence of fish sentience, since this issue is still being debated among biologists. However, most biologists are at present acknowledging the probability of fish being sentient creatures. Current aquaculture practices are affecting fish welfare during all four of the cited stages, both on physical and mental levels, as well as on the ability of fish to carry out natural behaviors. The effect fish farming has on the environment is here separated into five different categories: the decline of wild fish populations; waste and chemical discharge; loss of habitat; spreading of diseases; and invasion of exotic organisms. There is evidence of severe negative effects on the environment when looking at these five categories, even when considering the difficulty of studying environmental effects, due to the closely interacting variables. The ethical arguments and scientific evidences here reviewed have not all come to the same conclusions. Nevertheless, the general agreement is that current aquaculture practices are neither meeting the needs of fish nor environment. Thus, the obvious environmental and animal welfare aspects of finfish aquaculture make it hard to ethically defend a fish diet.

Assessing pollutant exposure in cultured and wild sea bass (Dicentrarchus labrax) from the Iberian Peninsula

The aquaculture industry is an expanding activity, mainly due to the world population demand of fish. However, intensive production and the use of chemicals have raised environmental concerns and have questioned the quality of cultured fish in comparison to wild fish. Up to date, there is little information regarding pollutant residues in cultured stocks and the risks associated to consumption. Here we summarize recent data on pollutants exposure, together with biochemical responses in both cultured and wild sea bass (Dicentrarchus labrax) from the Iberian Peninsula. The obtained data highlights the use of chemicals in current aquaculture practices as a significant source of pollution in cultured fish that poses a risk to exposed individuals and may negatively impact aquatic ecosystems. Nonetheless, a controlled use of those chemicals and a careful selection of the aquaculture location can ensure relatively low and homogeneous levels of pollutants in cultured fish in comparison to wild specimens.

Expert Judgments Regarding Risks Associated with Salmon Aquaculture Practices in British Columbia

Making sound decisions about managing ecological risks necessarily involves relying on judgments by technical specialists informed by the best available scientific evidence. Yet, organizing those judgments in ways to assess the relative risks of different components of a technology, and considering priorities in managing those risks, is a difficult and under‐explored aspect of environmental management. In this study, we elicited the judgments of scientists associated with the salmon aquaculture industry in British Columbia in order to learn their expert viewpoints of potential risks. This paper presents survey results regarding structured judgments provided by scientists engaged in studies associated with aquaculture or preserving wild stocks of Pacific salmon species. There were statistically significant differences regarding judgments of the risks of various current aquaculture practices on wild salmon stocks. It was possible to rank the means of scientific judgment scores to prioritize these risks. Differences in rankings were location and context specific.

The Potential and Sustainability of Aquaculture in India

ABSTRACT India is a very populous country with more than one billion people. In order to provide food for this growing population, serious environmental problems may result. Despite many benefits from the green, blue, and silver revolutions adopted in India, there has been much concern resulting from intensive agricultural practices that led to environmental problems in both terrestrial and aquatic ecosystems. Increasing demand for aquatic resources also caused inland fisheries to decrease over the past few decades. The location of aquaculture projects, landscape destruction, soil and water pollution by pond effluents, over-exploitation of important fish stocks, depletion in biodiversity, conflicts over agriculture and aquaculture among various stakeholder groups over resource and space allocation, and international fish trade controversies have threatened the long-term sustainability of fisheries and aquaculture industries. The subject of sustainable aquaculture has not been adequately projected in terms of current aquaculture practices aimed to boost a rural economy. This review briefly describes the key issues of aquaculture unsustainability in terms of intensive aquaculture, nutrient enrichment syndrome, soil and groundwater salinization, destruction of mangroves, loss of biodiversity, marine pollution and loss of fish stock, use of aquachemicals and therapeutics, hormone residues, etc. The strategies for sustainability have been highlighted with respect to rice-cum-fish culture, carp polyculture, integrated farming with livestock, rural aquaculture, intensification of small farms, wastewater-fed aquaculture, crop rotation, probiotics, feed quality, socioeconomic considerations, environmental regulations and fisheries acts, transboundary aquatic ecosystems, impact of alien species, ethical aspects of intensive aquaculture, responsible fisheries, and environmental impact assessment. A suggested model outlines the feedback mechanisms for achieving long-term sustainability through improved farm management practices, integrated farming, use of selective aquachemicals and probiotics, conservation of natural resources, regulatory mechanism, and policy instruments.

Early life characteristics of pike, Esox lucius, in rearing ponds: temporal survival pattern and ontogenetic diet shifts

Survival, biomass and diet of pike, Esox lucius, larvae and juveniles were studied over 3 years by stocking free embryos at a density of six fish m−2 in 12 drainable outdoor ponds. The ponds were sequentially drained at six larval/juvenile developmental stages, up to a total length (T.L.) of 139 mm. The mean rate of survival at harvest decreased irregularly over time and the highest mortality rates were recorded during the early larval period (13 to 27 mm t.l.) and two intervals of the juvenile period (46 to 99 mm T.L. and 121 to 139 mm t.l.). Mean biomass increased dramatically between 46 mm T.L. (19.8 kg ha−1) and 121 mm T.L. (181.8 kg ha−1) and stabilized between 121 and 139 mm t.l. Sharp increases in the mean weight coefficient of variation were recorded during the early larval period (13 to 27 mm t.l.) and between 74 and 121 mm t.l. (development of cannibalism). Diet breadths were relatively narrow in pike larvae and reached maximum levels in 99 mm t.l. juveniles. Average‐sized pike exhibited a sequence of size‐dependent shifts from a diet composed primarily (in terms of weight) of micro‐crustaceans (at 13 mm t.l.), to chironomid larvae (at 74 to 99 mm t.l.), and finally macrocrustaceans (at 121 to 139 mm t.l.). Cannibalism was detected first among the largest fish at the 74 mm t.l. stage. Between‐year diet similarity at various developmental stages was consistently high. In 70 mm t.l. fish harvested from different ponds, we found significant among‐pond differences in diet composition; however, similar trends of diet changes in relation to fish size were observed from pond to pond. Our results are discussed in light of existing knowledge of young pike trophic ecology and current aquaculture practices.