Reviews in Aquaculture

The paper reviews the following three types of mangrove‐shrimp systems: (i) integrated with canals between platforms planted with mangrove; (ii) associated having larger areas of water and a large mangrove area; and (iii) separated, with a dyke separating ponds from forest. The variations in shrimp yield of integrated and associated systems, that is, mixed systems, are attributable to water exchange, % water surface, primary production, stocking of post‐larvae, leaf litter fall and decomposition, species, cover and age of mangrove, and predators. Leaf litter from all mangrove species except Nipa palm adversely affect water quality. Leaf composition and decomposition rate vary between species; submersed leaves decompose faster. Low concentrations of decomposing leaves of certain species temporarily boosted shrimp growth. Shrimp yield has been found to be highest in ponds with 30–50% mangrove cover, but remained <400 kg ha⁻¹ year⁻¹, if not fed timber production peaked at 55% mangrove cover (about 10 m³ ha⁻¹ year⁻¹). Annual benefit–cost ratio was better in integrated systems than in associated systems, but one study found the reverse in a long‐term computation. An integrated mangrove‐shrimp farm of 4 ha may provide farmers with a decent livelihood in Vietnam, if contracts do not restrict recommended practices to keep water quality within the limits acceptable for shrimp. Separated systems, where mangroves are fully connected to open water, have more potential to contribute to ecological, economic and social sustainability. Enhancing the economic returns by capitalizing on ecosystem services through carbon credits and organic certification, will require support for initial investment and clustering of farms.

Nghiên cứu này điều tra các yếu tố quyết định việc áp dụng hệ thống canh tác lúa cá cải tiến tại đồng bằng sông Cửu Long để hỗ trợ cho việc xây dựng chính sách, quy hoạch sử dụng đất nông nghiệp và mở rộng mô hình lúa cá tích hợp. Gần đây, các hệ thống này được coi như là sự thích ứng với biến đổi khí hậu trong khi các hệ thống lúa cá truyền thống thường bị bỏ bê. Năm 2006, chúng tôi tiến hành khảo sát trên 94 hộ nông dân, hoặc trồng lúa độc canh hoặc có hệ thống lúa cá cải tiến. Chúng tôi đã phân tích dữ liệu bằng hồi quy logistic nhị phân và mô phỏng việc chấp nhận thông qua logic mờ. Thu nhập bình quân đầu người và trên mỗi hecta của các hộ gia đình áp dụng hệ thống lúa cá hầu như gấp đôi, trong khi qui mô trang trại lớn hơn 1,3 lần so với các trang trại độc canh lúa. Các hộ gia đình có diện tích canh tác lớn hơn, tức là có các thửa ruộng và ao tưới tiêu gần kề, tiếp cận tốt hơn với vốn tài chính và có kiến thức sâu hơn về nuôi trồng và tích hợp lúa và cá, có khả năng cao hơn trong việc áp dụng hệ thống lúa cá. Các động lực và yếu tố đã được xác định trước đó đối với việc áp dụng, chẳng hạn như bối cảnh nông sinh thái thích hợp và trình độ giáo dục và đào tạo của nông dân đã được xác nhận. Việc khuyến khích hệ thống lúa cá đòi hỏi các phương pháp khuyến nông và nghiên cứu có sự tham gia của các bên liên quan để phát triển các chiến lược nông nghiệp bền vững như quản lý dịch hại tổng hợp (IPM), trong đó nông dân, người hướng dẫn và các nhà nghiên cứu tối ưu hóa các công nghệ trong những bối cảnh liên tục thay đổi.

The presence of skeletal anomalies in farmed teleost fish is currently a major problem in aquaculture, entailing economical, biological and ethical issues. The common occurrence of skeletal abnormalities in farmed fish and the absence of effective solutions for avoiding their onset or definitely culling out the affected individuals as early as possible from the productive cycle, highlight the need to improve our knowledge on the basic processes regulating fish skeletogenesis and skeletal tissues differentiation, modelling and remodelling. Severe skeletal anomalies may actually occur throughout the entire life cycle of fish, but their development often begins with slight aberrations of the internal elements. Comprehensive investigation efforts conducted on reared larvae and juveniles could provide a great contribution in filling the gap in knowledge, as skeletogenesis and skeletal tissue differentiation occur during these early life stages. The aim of this review is to provide a synthetic but comprehensive picture of the actual knowledge on the ontogeny, typologies and occurrence of skeletal anomalies, and on the proposed causative factors for their onset in larvae and juveniles of European farmed fish. The state‐of‐art of knowledge of these issues is analysed critically intending to individualize the main gaps of knowledge that require to be filled, in order to optimize the morphological quality of farmed juveniles.

Coastal benthic ecosystems may be impacted by numerous human activities, including aquaculture, which continues to expand rapidly. Indeed, today aquaculture worldwide provides more biomass for human consumption than do wild fisheries. This rapid development raises questions about the interactions the practice has with the surrounding environment. In order to design strategies of sustainable ecosystem exploitation and marine spatial planning, a better understanding of coastal ecosystem functioning is needed so that tools to quantify impacts of human activities, including aquaculture, may be developed. To achieve this goal, some possible directions proposed are integrated studies leading to new concepts, model development based on these concepts and comparisons of various ecosystems on a global scale. This review draws on existing literature to (i) briefly summarize the major ecological interactions between off‐bottom shellfish aquaculture and the environment, (ii) introduce research on the influence of benthic diversity on ecosystem functioning (BEF relationships) and (iii) propose a holistic approach to conduct aquaculture–environment studies using a BEF approach, highlighting the need for integrated studies that could offer insights and perspectives to guide future research efforts and improve the environmental management of aquaculture.

Inland aquaculture of shrimp in low salinity waters is widespread in many regions worldwide. Owing to its ability to grow and survive in low salinity environments the Pacific white shrimp, (Litopenaeus vannamei Boone) has become the candidate of choice for low salinity culture. Remediation techniques have been developed to improve the osmoregulatory capacity of shrimp reared in low salinity waters. These techniques have evaluated water modification strategies that improve low salinity waters used for production by adding potassium and magnesium fertilizers and dietary approaches that involve modification of the feeds offered to shrimp with supplements that might improve osmoregulatory capacity. Based on our own experience as well as what we found predominantly in the literature, it appears that modification of the rearing medium with potassium and magnesium fertilizers is more effective than dietary modification techniques at improving the growth, survival and osmoregulatory capacity of shrimp reared in low salinity waters.

L‐carnitine is a multi‐functional nutrient which plays a leading role in fatty acid metabolism in mammals and other eukaryotes. Its main physiological function is to promote fatty acid β‐oxidation to produce energy, which reduces body fat content and improves body weight without affecting moisture content in whole body and muscle. In recent years, its dietary supplementation in aquaculture nutrition has been studied in different cultured species. It has been proved that L‐carnitine can improve growth and increase lipid utilization rate in some aquatic animals. However, such beneficial effects of dietary L‐carnitine are limited or absent in other species. The reasons for the conflicting results obtained on L‐carnitine functions in aquatic animals need to be elucidated. This review explores comprehensively the different physiological functions of L‐carnitine in various aquatic animals. In the end, research strategies are provided to elucidate the existing conflicts on dietary L‐carnitine application in aquaculture nutrition in order to promote its utilization in aquatic feed industry.

Molluscs are major aquaculture species worldwide. Molluscan aquaculture accounts for approximately 27% of the total world aquaculture production. The use and exchange of genetic resources have played an important role in the development of molluscan aquaculture. The introduction and use of non‐native species have been instrumental in oyster and scallop aquaculture; for example, the Pacific oyster, translocated from Japan, supports major aquaculture industries in many countries of North and South America, Europe, Asia and Africa. Bay scallops introduced from the USA account for an annual production of over 600 000 t in China. Non‐native genetic materials have also been used for the genetic improvement of native species through interspecific and intraspecific hybridization. Unique genetic lines, such as disease‐resistant strains, have been developed through selective breeding in some molluscs, although significantly more efforts are needed. Although the importance of genetic resources is apparent, the identification, protection and utilization of molluscan genetic resources remain a challenge.

Abalone is a highly valued seafood in many parts of the world. Depending on size and species, it can fetch between US$15 and US$30 per kg in some markets. Because of its high value, abalone is cultured in several countries, including China, Australia, Japan, Chile, South Africa, Canada, Mexico, the USA and many other Asian countries, such as Thailand, the Philippines and Korea. Hybridization is widely used to improve specific traits in animal and agricultural stocks by using a new genetic conformation in the offspring. In general, hybridization offers several benefits in aquaculture conditions, such as improvements in growth rate, survival, food conversion and stress resistance (to temperature and disease). Under commercial conditions, hybrids make it possible to diversify the industry and to offer new products and gain new markets. This review examines evidence of wild and experimental hybridization among abalone species from several biogeographical areas worldwide, and provides information on the phenotype characteristics of artificially produced hybrid abalone. Genetic and phenotypic approaches were analysed to determine whether there is a relationship between the genetic variability and positive heterosis in hybrid crosses. In this review, we also reported embryonic and larval development of hybrid and genetic studies derived from gene expression analysis of thermal tolerance. Furthermore, alloenzyme, cytogenetic and molecular DNA markers were reviewed to certify the hybrid status in Haliotis. This review will also discuss the impact of intra and interspecies hybrids on abalone aquaculture worldwide.

The worldwide use of Nile tilapia (Oreochromis niloticus Linnaeus, 1758) in aquaculture represents a somewhat unique scenario. The natural distributions and global genetic resources of tilapias are in Africa, yet the main centers of utilization for aquaculture are primarily in Asia. Within a few decades, Nile tilapia graduated from being an ‘orphan commodity’ (i.e. of interest to only resource‐poor fish farmers) to a globally traded commodity. Most aquaculture production of Nile tilapia in Asia and elsewhere has relied on a narrow genetic base. The natural genetic resources have not yet been fully documented and tapped for use in aquaculture, and many natural populations are under severe threat of irreversible change or loss. Although genetic improvement is now well underway, an important question is how the wealth of Nile tilapia wild genetic resources shall be used for the benefit of a wide range of users, at present outside Africa. This review focuses on documenting the status of Nile tilapia genetic resources (including the potential threats), providing a case for their conservation and for the judicious utilization of genetic diversity for the benefit of all stakeholders; and on analysis of the lessons learnt from a major Nile tilapia genetic improvement initiative, the genetic improvement of farmed tilapia (GIFT) project. Information about other genetic improvement efforts by means of hybridization, sex reversal and YY male technology is also presented.

Tridacnid giant clams are of commercial interest for their nutritional, economic, and ecological significance throughout theIndo‐Pacific andOceania. A major impediment to culturing tridacnid giant clams is larval mortality, typically >96%. The effects of suspended and particulate nutrients on tridacnid veliger development have been examined, but factors relevant to the nutritional condition of oocytes and trochophore larvae are unknown. This is significant because the nutritional transition from trochophore to veliger coincides with rises in larval mortality. Our review examines culture techniques known to enhance gamete viability of several marine viable bivalves of commercial interest, and critically assesses whether such methods are applicable to tridacnids in culture conditions. Techniques for optimizing the nutritional requirements of pre‐veliger tridacnids such as broodstock conditioning by supplemental feeding, monitoring the condition of oocytes ready for release, water temperature, egg attributes such as size and biochemical composition, and nutrient loads in culture water chemistry are examined. We include suggestions for optimizing nutritional conditions from gametogenesis through embryonic development, and conclude with a primer of research opportunities based on gaps in our understanding of tridacnid pre‐veliger nutrition compared with other bivalves. A major conclusion is that culture protocols should include pre‐veliger nutritional fitness as a critical factor in enhancing larval survival, growth and development.