Today, keeping fish alive for eventual consumption is a common fish-handling practice worldwide. To do so, fish are first conditioned in a container with clean water, while the damaged, sick and dead fish are removed. Fish are starved and, if possible, water temperature is lowered in order to reduce metabolic rates and make fish less active. Low metabolic rates decrease the fouling of water with ammonia, nitrite and carbon dioxide that are toxic to fish and impair their ability to extract oxygen from water.
Handling live fish
A large number of fish species are usually kept alive in holding basins, floating cages, wells and fish yards. Holding basins, normally associated with fish culture companies, can be equipped with oxygen control, water filtering and circulation and temperature control. Simpler methods are also used. For instance, large palm woven baskets act as floating cages in rivers (China) or simple fish yards are constructed in a river's backwater (South America). Also, the transportation of live fish ranges from very sophisticated systems installed on trucks that regulate temperature, filter and recycle water and add oxygen, to very simple artisanal systems of transporting fish in plastic bags with an atmosphere supersaturated with oxygen.
Handling dead fish
For dead fish, handling operations after capture are: transferring catch from gear to vessel, holding of catch before handling, sorting/grading, bleeding/gutting/washing, chilling, chilled storage, unloading. These operations can be performed in several ways, from manual methods to fully automated operations. The number of operations and the order in which they are performed depend on the fish species, the gear used, vessel size, duration of the voyage and the market to be supplied.
It is crucial to provide a continuous flow in handling and to avoid any accumulation of unchilled fish, thereby bringing the important time-temperature phase under complete control. It is also essential to improve working conditions onboard fishing vessels by eliminating those catch-handling procedures that cause physical strain and fatigue to fishers. Nowadays, this is possible in industrial fisheries because of equipment and handling procedures designed to eliminate heavy lifting, unsuitable working positions and rough handling of fish.
Icing is the oldest method of preserving fish freshness. Currently, it is widely used thanks to mechanical refrigeration, which makes ice readily and cheaply available. In addition, ice keeps fish moist, has a large cooling capacity, is safe, is a portable cooling method that can be easily stored, transported and used by distributing it uniformly around fish. Ice can be produced in different shapes - the most commonly used to cool fish are flake, plate, tube and block. Block ice is crushed to chill fish.
For artisanal fisheries, FAO developed appropriate handling technologies to preserve fish freshness. The cost-effective use of ice on small boats, pirogues, canoes, etc. in tropical areas has only been possible through the introduction of insulated containers - especially in tropical, warm climates. These containers are designed and constructed locally, using natural or artificial insulating materials, with enough handling flexibility. Two very interesting cases are the introduction of insulated fish containers in the pirogue fleet of Senegal and onboard "navas" - the traditional fishing vessels of Kakinada in Andhra Pradesh, India. The Senegalese example has spread steadily to comparable fisheries in West Africa (Gambia, Guinea-Bissau and Guinea) that have adopted the use of similar insulated containers.
After landing, fish handling procedures are similar to those described above. They often include sorting/grading, gutting/washing, chilling, chilled storage, unloading. These operations can also be done manually or using fully-automated operations.