5.9 explain the methods which are used to farm large numbers of fish to provide a source of protein, including maintenance of water quality, control of intraspecific and interspecific predation, control of disease, removal of waste products, quality and frequency of feeding and the use of selective breeding.

Fish is a good source of protein which is why humans consume large amounts of fish. They are also a good direct source of energy and low in fat. The demand for fish is increasing, the increased demand has caused overfishing and has seriously affected the populations of fish being caught for food.

Technology such as sonar tracking, drift netting, mesh nets catch many different types of species. These species are caught and killed disrupting the marine ecosystem. As the fish are not given enough time to reproduce and replenish in numbers, the population starts to decrease.

Fish farming is a more effective method which allows humans to produce a sustainable stock. To be able to control the quality and yield of fish, the conditions in which the fish are raised must be monitored.

Maintenance of water quality:

Water quality needs to be monitored in fish farms to control and limit the contact of harmful chemicals with the fish, so there are no indigestible substances in the water which may decrease the yield of fish. The water also needs to be cleaned regularly to maintain high oxygen levels in the water, reduce the spread of disease and to remove waste build up below the farm, which leads to eutrophication.

Water quality can be maintained by circulating fresh/sterile water throughout the enclosure and filtering systems. Aeration systems can be used to maintain high O₂ levels

Interspecific and Intraspecific predation:

Fish need to be separated in fish farms to avoid interspecific and intraspecific predation/competition.

Intraspecific – same species. E.g. salmon and salmon

Interspecific – different species. E.g. salmon and tuna

 Fish are usually separated by size, age, gender and species.

-        Separating fish by species stops interspecific competition.  

-        The numbers of fish in the enclosure must be monitored to avoid intraspecific competition (competition between fish of the same species).

-        Separating them by gender, unless they are breeding, prevents unwanted new fish.

-        Fish of different sizes and ages being separated can help limit intraspecific competition.

Prevention of interspecific competition:

-        Fencing off the area that the fish are in.

-        e.g. nets or keeping the fish in tanks

Prevention of intraspecific competition

-        Separating the fish by, size, age and gender

-        Feeding fish regularly

-        Giving the fish enough room

Control of disease:

In fish farms there is a greater risk of disease because all the fish are living close together and selective breeding. Since there are large amounts of fish being kept together, disease spreads easily.

The fish are all closely related, due to selective breeding the fish may have the same or similar vulnerabilities and therefore are all effected by the diseases in similar ways. To control disease, fish farms need to keep the fish in smaller amounts and have to spend money on supplying sterile water, pesticides and antibiotics, which can be very expensive.

Removal of waste products:

The removal of waste products is important in maintaining sterile water and control of disease. The large amounts of waste need to be removed regularly and cause a disruption of the environment in the water surrounding the farm.

There are many ways to remove waste products such as, changing the water of the enclosure or moving the location of the fish. However, most farms will use systems to filter the water and the waste products (faeces and uneaten food etc.) will be dumped into water outside of the enclosures and leads to eutrophication.

*having a circulation of water can be a way to remove waste products

Quality and frequency of feeding:

The fish in captivity are fed with pellets made of other less valuable fish (often wild fish). They are fed in small amounts at regular intervals, so there is less food wasted. Sometime fish are over fed or fed with high protein foods to increase growth rate.

Selective breeding

Using selective breeding, fish farmers can breed fish with more ideal traits. By breeding the fish with the best traits such as growing very big, farmers can breed a new generation of fish that grow faster and bigger, have high quality meat and better survival rates.

Fish farms summary:

Pros:

-        Controlled water quality

-        Protection against predators

-        Keeps competing species out (provides safety)

-        Frequent feedings allow for rapid growth

Cons:

-        Greater risk of disease (because selective breeding/ closely related and high density + living close together)

-        Sterile water, pesticides and antibiotics are needed to control disease (expensive)

-        Large amounts of waste products – need to be removed regularly and may cause eutrophication

-        Fish fed with pellets made of other smaller/less valuable wild fish. Can cause damage to wild fish stocks