Practical Notions on Fish Health and Production

Besides basic anatomical and physiological features common to all fishes, due to the aquatic environment they share, there are some very significant differences. Such differences range from major ones common to all species within each main group, namely cyclostomes, chondrichthyans and osteichthyans, to more limited ones between different species within each group. Even the latter can be very significant, conditioning, for instance, the feeding behavior/strategy of a given species or its reproductive ability. Some of the main anatomical and physiological features of the different fishes are briefly reviewed, since a good knowledge of such features is crucial to understand the behavior of each species in the wild and/or to assure the most correct management of its populations either in captivity or in the wild.

Fishes have a great diversity of reproductive strategies and associated traits, as well as complex life-cycles with multiple stages. This chapter briefly introduces different, commonly found, reproductive strategies and focus mainly on the early stages of fish life cycles, in particular eggs and larvae. Most fishes are iteroparous, spawning several times during their life, but some species, semelparous, adopt an extreme strategy, spawning only once in their life cycle.

There is a great diversity of fish egg types and adaptations, and they can be classified as either pelagic or demersal, depending on where they occur in the environment. The embryonic development depends on the species, and also on abiotic factors such as temperature, oxygen and salinity. The ontogenetic development that starts during the embryonic stage continues during the larval life. During this phase, fundamental structural and functional changes will occur in a short period, increasing the larval abilities to interact with the environment. Depending on the species reproductive strategy and life history, newly hatched larvae can vary from very small and poorly developed, to larvae that hatch larger with developed sensorial and functional capabilities; some larvae can even resemble the adults at hatching.

Farmed fish have been produced for more than four thousand years, but the most significant developments only arise in the last 50 years. Nowadays, fish and crustacean obtained in aquaculture systems represent almost 45% of all the fish products placed in the global market, about 160 million tons. Aquaculture involves human intervention in the life cycle of the cultivated organisms, and requires special techniques applied to housing, reproduction, feeding, fattening, healthcare and package to market distribution. The fish farms location depends on the species, space availability, climatic characteristics and environmental impacts. Most common regimes of exploitation are intensive, especially when they are intended for productions to be placed on the global market. Different production systems have distinct requirements in terms of ecological, reproductive and sanitary management, and their control is mandatory for the economic success of the aquaculture system. Health management is a key issue for the success of animal exploitation system.

Diseases of fish, caused by biological agents (bacteria, fungi, virus or parasites), are better known in farmed or ornamental fish, since the access to the affected fish coming from the natural environment is less probable. In fact, the fish that are infected by a specific pathogenic agent, natural inhabitants of the marine, estuarine or freshwater ecosystems, are rapidly eliminated from its biotopes by other predatory animals, due to its higher vulnerability and susceptibility to the social interactions.

Diffusion of pathogenic bacteria, fungi, virus or parasites in the aquatic environments is more efficient than in the terrestrial ones. Diagnosis and therapeutics of fish disease have specific difficulties and the application of preventive measures is a very complex issue. Some of those diseases have the same epidemiological problems of the infectious diseases of the terrestrial animals: High spread of diffusion, very significant economic losses, restrictions to fish travel or commerce and some (few) have zoonotic impacts.

Handling and manipulation of fish, requires, almost without exception, sedation or anaesthesia due to integument fragility and health as well as welfare considerations.

Integument adaptations to fish immersed life such as thin epidermis covered with a protective layer of mucous, intradermic scales and slender hypodermis must be protected during physical manipulations. Also, as sentient animals, fish must be spared the eventual pain and stress caused by husbandry, research and veterinary procedures.

Fish anaesthesia and surgery have become common procedures in ornamental fish industry, public aquaria and research, and in the case of anaesthesia and aquaculture.

Surgery is one of the reasons to anesthetize fish as these animals can undergo a variety of surgical procedures, from simple cutaneous interventions to more sophisticated intracoelomic and even cardiac or hepatic surgeries.

World fish production is growing due to an economic growth of developing countries, where the population has greater access to expensive animal protein. The livelihoods and income provided to those involved in the fisheries production and subsidiary activities is bigger than that provided by the agriculture. The substantial demand for fish and fish-based products and overcapacity of fishing fleets are, in turn, responsible for the overexploitation of marine resources and for the negative impact on the economy and wealth of the communities living on fisheries. A proper management of marine resources is important in order to avoid multilevel problems, such as ecological, economic, food security and people’s wealth. The international trade in fish and fishery products must comply the WTO agreements and with the guidance documents developed by the Codex Alimentarius Commission. Maintaining the cold chain is one of the largest contributors to the improvement of the international fish trade. Some fishing vessels are adapted to a single method of catch or fishing gear, in spite of many of them being versatile and equipped for polyvalent captures. Regarding the hygiene requirements and the operations carried out on board to the fishery products, the fishing vessels are classified as primary production vessels, freezer vessels and factory vessels. These categories are independent of the size of the vessel or fishing gear and methods used. The most important is to carry out all the operations on board hygienically to maintain the sanitary quality of the product, avoid contaminations and minimize spoilage by temperature abuse.

Fish and shellfish products have been used as food supply since immemorial times. Earliest evidences show that for more than one million years ago, manual capture of gastropods and bivalves bordering the sea shore waterfront have been crucial for survival, development and increasing of human communities. Fish products are a unique source of rich nutrients, being easy to digested, representing a very relevant source of indispensable amino acids, fatty acids, minerals and vitamins for many millions of people worldwide. However, only products obtained from healthy fish and maintained in hygienic environments are suitable for consumption and can present those nutritional advantages. If such products are not handled and or correctly processed, consumer health may be put at risk.

Many fish preservation technologies are based on multiple hurdles used to inhibit or reduce biochemical changes and microbial contamination that leads to spoilage. This chapter aims to describe some of the most traditional technologies currently applied to fishery products based on the control of water activity, pH, oxidereduction potential, temperature, relative humidity and gaseous composition of the atmosphere. Emergent technologies, such as Ohmic heating and microwaving; amongst others, can be seen with particular interest for future application at industrial scale. In fact, the combination of traditional and emergent technologies (thermal or non-thermal processes) in processed fishery products, might be the trend to achieve and supply safer and high quality products.