Sustainable aquaculture and aquatic resources management

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Published on 27/3/2017

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Published on 27/3/2017

Nutrition in ornamental aquaculture: the raise of anthropocentrism in aquaculture?

Published on 23/3/2017
Ornamental aquaculture nutrition is profoundly different from conventional aquaculture nutrition from several points of views as the prices, finality and diversity. This paper tries to answer to some simple questions: do modern ornamental fish feeds reflect more physiological fish needs or aquarist expectations? What are the driving forces behind the modern aquarium nutrition? On the light of the considerations made in this paper, it emerges that popularity of ornamental aquaculture is largely influenced by a progressive humanization of ornamental fish. Obesity and longevity transfer is the most evident nutritional effect of pet proximity to humans and this special kind of ‘contagion’ is observable in ornamental fish too. Assuming that aquarium fish have been humanized, ornamental fish industry has taken profit from this. A drastic change happens to fish feeds after crossing the human doorstep. This is probably ignored by humans, but not by ornamental aquafeed companies that sometimes induce erroneous customer expectations to improve their profits. Feeding an ornamental fish in our modern society represents a symbolic action more referred to humans than to fish physiological needs; therefore, human psychology affects the ornamental fish feeds quality much more than the fish physiology. This is the main and illogical conclusion of this paper. This paper tries to enlighten some unexpected relationship between us (humans) and this modern category of domesticated animals: aquarium fish and to give some possible future perspectives.

Plant essential oils as fish diet additives: benefits on fish health and stability in feed

Published on 23/3/2017
Nutritional strategies focused on the use of phytochemicals as modulators of immunological and physiological responses, as well as antistress and antioxidant therapies and health promoters of the gastrointestinal tract have attracted increased interest in animal production. Over the past two decades, several studies have reported positive results of using plant essential oils (EOs) as dietary additive in several farm animal species. Recently, these nutritional alternatives have been evaluated and reported in fish production in order to enhance the resistance to diseases and prevent outbreaks, as well as to improve fish growth, animal welfare and feed utilization. However, despite the diverse and relevant biological activities reported, these phytochemicals are composed of often unstable and volatile molecules, which makes the chemical and physical characteristics of the EOs important aspects to be considered in fish nutrition research. This review summarizes the current knowledge regarding the use of plant EOs as fish dietary additives, focusing on their potential as modulators of the gut bacterial community and discussing some aspects regarding their stability in feeds.

Protein phosphorylation and ions effects on salmonid sperm motility activation

Published on 23/3/2017
Sperm motility is considered as a key factor allowing determination of semen quality and predicts fertilizing capacity. In many fish species, the spermatozoa are immotile in the testes and seminal plasma, and motility is induced when they are released in the aqueous environment. Initiation and activation of sperm motility are prerequisite processes for the contact and fusion of male and female gametes at fertilization. Many proteins are involved in the activation of sperm motility in many species. Cell signalling for the initiation of sperm motility in the salmonid fish has drawn much attention during the last two decades. In some species, protein phosphorylation process was shown to be involved in flagellar motility regulation. Hyperpolarization of the sperm membrane induces synthesis of cAMP (cyclic AMP), which triggers further cell signalling processes, such as cAMP-dependent protein phosphorylation that finally initiates sperm motility in salmonid fish. Ions such as Na+, K+ and Ca2+ play also an important role in the activation of sperm motility in many species, more specifically in salmonids. Salmonid fish sperm motility can be suppressed by millimolar concentrations of extracellular K+, and dilution of K+ upon spawning is enough to trigger the cAMP-dependent signalling cascade leading to motility initiation. This review aims to update the present knowledge about the roles of ions and protein phosphorylation process in the sperm motility activation in salmonids.

Use of lumpfish for sea-lice control in salmon farming: challenges and opportunities

Published on 9/3/2017
Efficient sea-lice control remains one of the most important challenges for the salmon farming industry. The use of wrasse (Labridae) as cleaner fish offers an alternative to medicines for sea-lice control, but wrasse tend to become inactive in winter. Lumpfish (Cyclopterus lumpus) continue to feed on sea-lice at low temperatures, and commercial production has escalated from thousands of fish in 2010 to well over 30 million juveniles deployed in 2016. However, production still relies on the capture of wild broodstock, which may not be sustainable. To meet global industry needs, lumpfish production needs to increase to reach c. 50 million fish annually and this can only come from aquaculture. We review current production methods and the use of lumpfish in sea cages and identify some of the main challenges and bottlenecks facing lumpfish intensification. Our gap analysis indicates that the areas in most need of research include better control of maturation for year-round production; formulation of appropriate diets; artificial selection of elite lines with desirable traits; and development of vaccines for certified, disease-free juvenile production. The welfare of farmed lumpfish also needs to be better quantified, and more information is needed on optimal densities and tank design. Finally, the risk of farmed lumpfish escaping from net pens needs to be critically assessed, and we argue that it might be beneficial to recover cleaner fish from salmon cages after the production cycle, perhaps using them as broodstock, for export to the Asian food markets or for the production of animal feeds.

Risk of waterborne virus spread – review of survival of relevant fish and crustacean viruses in the aquatic environment and implications for control measures

Published on 19/2/2017
Aquatic animal diseases are a major constraint for increasing aquaculture production. Understanding the contribution of pathogen spread from infected aquaculture sites is critical in devising control measures in the event of an outbreak. We have reviewed the available literature on the persistence in the aquatic environment of several important viral pathogens of fish and crustaceans. These include infectious haematopoietic necrosis virus, viral haemorrhagic septicaemia virus, infectious salmon anaemia virus, koi herpes virus, epizootic haematopoietic necrosis virus and infectious pancreatic necrosis virus, white spot syndrome virus (WSSV), Taura syndrome virus and yellow head virus. Some trends were common to all viruses: (i) viability declined with increasing temperature (at temperatures above 0°C); (ii) higher biological loading in water correlated with reduction in detectable viable viruses; and (iii) virus decay in water is a function of time. Most aquatic animal viruses (AAVs) remained viable for several days or weeks. WSSV is particularly stable. Comparison of studies investigating survival parameters was sometimes difficult because of the different methods employed and different ways in which the data were presented. Data gaps are identified and experimental methods employed for testing critically assessed. The information presented in this review is directly relevant to design effective control measures for AAVs and to explore measures that reduce the economic impact of disease caused by these important pathogens.

Aquaculture of two commercially important molluscs (abalone and limpet): existing knowledge and future prospects

Published on 7/2/2017
Molluscan aquaculture produces the most food fish by volume in the global mariculture market. The historical, cultural and ecological value of molluscs makes them a highly sought-after delicacy in many regions of the world. Specifically, the aquaculture of abalone and that of limpets are two key industries with striking similarities and importance within the context of food production and food security. In this review, the current knowledge of these two commercially important seafood species is explored for a comprehensive understanding of its aquaculture status. The various culture methods and systems, animal nutrition and necessary improvements are discussed for abalone and limpets, respectively. For abalone, the knowledge base is extensive and some reviews have been written to compile essential information regarding different aspects of this healthy industry. For limpets, there is a small collection of aquaculture literature, and this is, to the authors’ knowledge, the first comprehensive review of the research. Our goal was to reveal, within the area of aquaculture research, the current status of both abalone and limpet industries while exposing their respective knowledge gaps for appropriate development of new technologies. With a firm understanding of these molluscs, the production of abalone and limpet will be sustainable for the long term.

Applications of genotyping by sequencing in aquaculture breeding and genetics

Published on 4/2/2017
Selective breeding is increasingly recognized as a key component of sustainable production of aquaculture species. The uptake of genomic technology in aquaculture breeding has traditionally lagged behind terrestrial farmed animals. However, the rapid development and application of sequencing technologies has allowed aquaculture to narrow the gap, leading to substantial genomic resources for all major aquaculture species. While high-density single-nucleotide polymorphism (SNP) arrays for some species have been developed recently, direct genotyping by sequencing (GBS) techniques have underpinned many of the advances in aquaculture genetics and breeding to date. In particular, restriction-site associated DNA sequencing (RAD-Seq) and subsequent variations have been extensively applied to generate population-level SNP genotype data. These GBS techniques are not dependent on prior genomic information such as a reference genome assembly for the species of interest. As such, they have been widely utilized by researchers and companies focussing on nonmodel aquaculture species with relatively small research communities. Applications of RAD-Seq techniques have included generation of genetic linkage maps, performing genome-wide association studies, improvements of reference genome assemblies and, more recently, genomic selection for traits of interest to aquaculture like growth, sex determination or disease resistance. In this review, we briefly discuss the history of GBS, the nuances of the various GBS techniques, bioinformatics approaches and application of these techniques to various aquaculture species.

Sugars as supplemental cryoprotectants for marine organisms

Published on 4/2/2017
Cryopreservation has been extensively used in various mega-industries and has recently been applied in genetic banking for conservation purposes. Compared with conventional cell preservation methods, cryopreservation can maintain the viability of cryopreserved cells for an indefinite time at a relatively lower cost and lesser manpower, with lower probabilities of contamination and genetic changes. This study presents the crucial role of sugar, a cryoprotectant supplement in cryopreservation. Sugar molecules typically interact with the lipid bilayer during the freezing phase to maintain plasma membrane integrity when cells undergo dehydration. When combined with other permeable cryoprotectants such as glucose with methanol and trehalose with dimethyl sulphoxide, sugar prolongs and enhances cellular post-thaw viability. Moreover, terrestrial and marine organisms have benefited from the inclusion of sugar in the cryopreservation protocol. For wide range of cells such as the sperm, oocytes, embryos and larvae of marine vertebrates and invertebrates, as well as marine algae, cryopreservation with sugar produced positive results compared with cryopreservation without sugar. Not all sugar is beneficial, and the type and concentration of sugar should be applied according to the species. Moreover, the freezing method may also affect the function of sugar. Nevertheless, understanding the role of sugar in cryobiology and conducting a preliminary trial of sugar for cryopreserving cells would benefit future research on cryopreservation.

A comprehensive review of Vibrio (Listonella) anguillarum: ecology, pathology and prevention

Published on 2/2/2017
Vibrio (Listonella) anguillarum is a marine bacteria that is pathogenic to a number of aquatic organisms including several species which are important to the aquaculture industry. Organisms that are infected by V. anguillarum are diagnosed with vibriosis which can be lethal in a matter of days. Vibriosis can be particularly devastating to aquaculture businesses and measures of prevention or treatment are generally quite expensive. Efforts to understand and control V. anguillarum virulence have been of high-priority among international aquatic research studies. The knowledge that has accumulated as a result of this collective research effort is reviewed in this article.

Progress in fish gastrointestinal microbiota research

Published on 2/2/2017
The gastrointestinal (GI) microbiota of vertebrates plays critical roles in nutrition, development, immunity and resistance against invasive pathogens. In the past decade, research of the GI microbiota of mammals has drastically increased our knowledge on the microbiota and their relationship with health and disease. However, our understanding of fish intestinal microbiota is limited. This review provides an overview of research on fish gut microbiota, including microbial composition, formation, factors that affect the GI microbes and characteristics of fish intestinal microbiota compared with human and mice. Further, the updated research on gnotobiotic zebrafish is elaborated and the insights gained on functions of the fish intestinal microbiota are discussed. Understanding the intestinal microbiota of fish will guide the development of probiotics, prebiotics and hopefully probiotic effectors as novel additives to improve the health of fish.

RNA interference in shrimp and potential applications in aquaculture

Published on 29/12/2016
As the RNA interference mechanism was discovered, researchers have made huge strides in unravelling biological mechanisms at the gene level in a wide range of organisms. RNAi is a simple and rapid method that allows silencing gene expression at the post-transcriptional level and is triggered by the introduction of double-stranded RNA into the cell, leading to the degradation of the corresponding mRNA. In this review, we will provide an overview of successful RNAi experiments to date in Crustacea, and shrimp in particular, with special focus on various potential applications of RNA interference in research and aquaculture. An important aspect of RNAi in any species is the delivery of the double-stranded RNA and the barriers that have to be overcome to get the dsRNA into the target cells. Different options, experimental procedures, success rates and challenges in using RNAi are discussed in this review.

A meta-analysis of integrated multitrophic aquaculture: extractive species growth is most successful within close proximity to open-water fish farms

Published on 29/11/2016
Fish farming in open water releases dissolved and particulate waste (inorganic and organic) into the surrounding marine environment. To reduce this environmental impact, commercial extractive species can be grown alongside to utilize and reduce this waste, a technique known as integrated multitrophic aquaculture (IMTA). Information is lacking on whether (i) IMTA is generally successful with respect to extractive species growth responses and (ii) at what spatial scale they can be cultivated from fish cage nutrient sources. Focussing on bivalves and macroalgae as extractive species, this study uses a meta-analysis approach to summarize and conclude peer-reviewed data on IMTA to address these information gaps. We show that there are clear benefits to integrating bivalves and macroalgae with fish farms. Bivalves grown within, and relatively near, fish cages (0 m and 1–60 m distance categories, respectively) showed significantly higher biomass production relative to controls compared to those grown at larger spatial scales (61+ m). However, biomass production of macroalgae was significantly higher than controls only within close proximity to fish cages (0 m). This information shows increased extractive species production is generally greatest at relatively small spatial scales. It also highlights the need for more site-specific information (e.g. seawater parameters, hydrodynamics, food supply, farm capacity) in future studies. The allocation of control sites and locating these at suitable distances (>1–8 km) from fish farm effluent sources to avoid fish farm nutrient contamination are also recommended.

Overview of 3 year precommercial seafarming of Macrocystis pyrifera along the Chilean coast

Published on 23/11/2016
Chile is one of the main producers of seaweeds in the world; however, most of the production comes from harvesting natural beds and only 2.4% from cultures, dominated by the agarophyte Gracilaria chilensis. One of the most exploited resources is the giant kelp Macrocystis pyrifera, which is sold fresh for abalone feed and dry for alginate extraction. Recently, new possible markets are developing for this species, for example human consumption and biofuel/chemical production that could increase the demand and justify the development of a commercial cultivation system. The objective of this work was to present the recent development of the seafarming of M. pyrifera in Chile, focusing on the fundamental determinants of productivity in cultivated systems and the identification of the binding constraints to productivity. Three experimental plots (up to 21 Ha) were designed and deployed in three study areas (Caldera in northern Chile and Quenac and Ancud in southern Chile) to test different environmental conditions. During a period of 3 years, sporophytes produced in an indoor hatchery were deployed monthly, at different densities, and followed until harvest. Environmental parameters and biomass were monitored on a monthly basis. Our findings demonstrate the feasibility of Macrocystis seafarming on a large scale in Chile. Important differences in yield were observed between the study areas associated with either environmental physical or biological factors, such as the presence of herbivores. Our best production cycle reached 124 WMT Ha−1 month −1 in southern Chile, and the worst, less than 20 WMT Ha−1 month−1 in northern Chile. Finally, some direct and indirect constrains were encountered, including seeding season and depth, and the presence of pests and diseases, that are discussed.

Toxic effects of nitrite on freshwater organisms: a review

Published on 6/11/2016
High nitrite concentrations may occur mainly in recirculating aquaculture systems, but can also be found under certain conditions in natural waters. Among studied freshwater organisms, molluscs and worms followed by fish are the most resistant to nitrite. On the other hand, crustaceans and aquatic insects followed by amphibians are the most sensitive. Wide interspecific differences in nitrite susceptibility can be found within freshwater insects, crustaceans and amphibians. Chloride concentration in water is supposed to be the most important factor influencing nitrite toxicity. Generally, a positive chloride effect on nitrite toxicity reduction can be expected in all aquatic animals (or their early stages) employing gills for breathing and ion exchange. This phenomenon has already been observed in an amphipod (Eulimnogammarus toletanus, Pinkster & Stock), a planarian (Polycelis felina, Dalyell), two species of crayfish, several fish species and in amphibians in early development stages. A relatively huge amount of data on nitrite effects is available for fish, but other freshwater organisms were less frequently studied. Information on chronic effect of nitrite is nearly completely missing.

Use of bacterial subcellular components as immunostimulants in fish aquaculture

Published on 25/10/2016
Aquaculture and fisheries products are expected to play a leading part in addressing the food necessities of the increasing human population. However, in intensive aquaculture, fish are exposed to stress conditions that deteriorate their immune systems, leading to increased disease vulnerability. These disease outbreaks have resulted in production losses and represent one of the key constraints in fish farming. Accordingly, aquaculture disease management efforts have concentrated on the establishment of environmental friendly and lasting methods. Recently, several studies have revealed that various bacteria (especially probiotics)-derived cellular components might be used as promising immunostimulants in fish aquaculture. Such components curtail the risk concomitant with the use of antibiotics, chemotherapeutics, vaccines and probiotics. Among the various health advantages ascribed to bacterial cellular components, the modulation of specific and nonspecific immune responses, cytokine gene expression and anti-pathogenic activities are most anticipated benefits. Their potential as vaccine adjuvants for fish culture has also been demonstrated. However, as an emerging practice, limited knowledge is available regarding the detailed interactions with fish immune systems. Therefore, the underlying mechanisms involved in fish immune cell activation need to be explored further. In this context, the present article aspires to review the available studies on the use of bacterial cellular components in fish culture and their biological effects on fish such as growth promotion, immunostimulation and anti-pathogenic activities as well as to evaluate the factors that control the optimal induction of immune responses in fish. In addition, future issues that merit further investigation are suggested.

A revisit to fishmeal usage and associated consequences in Chinese aquaculture

Published on 22/10/2016
China has dominated global aquaculture production for more than two decades. Aquaculture production in China increased from 24.6 million metric tons (mmt) in 2000 to 47.5 mmt in 2014, an increment of 93.1%. Along with the fast-growing aquaculture industry, aquafeed production in China increased from 5.1 mmt in 2000 to 19.0 mmt in 2014, an increment of 272.5%. However, despite the rapid increase in aquafeed production, the fishmeal usage in aquafeeds in China has remained stable over the years. Fishmeal imports into China remained relatively steady at 1.0–1.5 mmt per annum from 2000 to 2014. An often unacknowledged fact is that China contributes more than 60% to the world aquaculture production at a cost of only 25–30% of the world fishmeal output. This review attempts to explain why the fishmeal usage has not increased proportionately with the increasing aquafeed production in China from several angles: (i) the current status of fishmeal usage in Chinese aquaculture; (ii) the relationship between the decreasing dietary inclusions of fishmeal and improved feed techniques, especially the use of alternative protein sources for fishmeal; (iii) the dominance of Chinese aquaculture by low trophic level species of plants, filter feeders, herbivores and omnivores and consequent low demands for fishmeal; and (iv) the increasing price of fishmeal and the management of exploitation of wild fisheries in the main fishmeal exporting countries to China. The trends and prospects of fishmeal usage in the future in Chinese aquaculture and the associated consequences are also addressed. Like other countries, China is now actively developing both resource conservation-based capture fisheries and environment-friendly freshwater and marine aquaculture systems. Aquaculture will be the main source of aquatic food in the future and will also indirectly contribute to save the world wild fisheries, and China will be main player that will continue to contribute towards this end.

Abalone growth and associated aspects: now from a metabolic perspective

Published on 9/10/2016
Worldwide, there are approximately 100 Haliotis species, more commonly known as abalone or ‘Paua’ in New Zealand, ‘Venus's-ears’ in Greece, ‘Awabi’ in Japan, ‘Perlemoen’ in South Africa and ‘Ormers’ in Europe. Regardless of what they are called in any part of the world, a high monetary value is coupled to this animal, because it is largely considered a seafood delicacy. Subsequently, a great deal of research primarily focused on improving the health and growth rates of abalone were carried out to maximise productivity of the commercial farming efforts in various countries. In this review, we comprehensively describe the most recent available scientific literature on abalone biology, and those aspects related to the growth of this organism; more specifically, those factors related to the uptake and breakdown of metabolic products which ensures long-term growth. We subsequently discuss this in terms of basic animal design, farming outcomes, feeding, cellular growth mechanisms and the unique metabolic processes that exist in these species. Using this information and the knowledge of the metabolic processes in other organisms, we additionally make a number of new hypotheses regarding how these metabolic processes may function in terms of abalone growth. Based on the information presented in this review, we also identify major research opportunities and gaps in the existing knowledge of abalone metabolism, which when elucidated may not only serve the purpose of better understanding these organisms growth but also could potentially lead to increased productivity of the abalone commercial farming sector.

Occurrence of mycotoxins in commercial aquafeeds in Asia and Europe: a real risk to aquaculture?

Published on 8/8/2016
There is increasing awareness of the negative effects of mycotoxins in aquatic species, which is highlighted in recent publications. Partly due to climate change associated with an overall increase of mycotoxins contamination in plant ingredients, and also due to the tendency to replace expensive animal-derived proteins, such as fish meal, by more economical plant proteins sources, which increases the probability of mycotoxin contamination in aquaculture feeds (Hooft et al. ). Over a 1-year period, 41 samples of finished aquaculture feed, both shrimp and fish, were analysed within the scope of BIOMIN mycotoxin survey programme. The samples were tested for aflatoxins, zearalenone, deoxynivalenol, fumonisins and ochratoxin A. Samples were sourced in Asia (31 samples) and Europe (10 samples) from fish/shrimp farms or feed producers. The values detected pose a risk for several important aquaculture species, assuming single mycotoxin contamination, that is excluding possible additive and synergetic effects between mycotoxins. Co-occurrence of mycotoxins in feeds may induce synergistic effects and increase the negative impact of mycotoxins in aquatic-farmed species at lower levels than when present in single contamination. This review gives an overview of the different mycotoxins and revises the effects of mycotoxins in aquatic species. Additionally, it reports the levels of mycotoxins in aquafeeds in 2014 and compares detected levels with possible negative effects in fish and shrimp. As it is highlighted by the results of the survey, the risk of co-occurrence is high and the knowledge on the effects of multimycotoxins contamination in aquatic species is basically none.

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