Fish Feeds (Aquaculture)

A major factor in sustaining a vibrant aquaculture sector is the ability to use the right fish feed. Among the various fish feeds available, plankton remains the most desirable and it is an essential ingredient or component in cultivating a sustainable symbiotic culture. Plankton is best described as diverse microorganisms that live in water.

Their microscopic composition makes them susceptible to water currents and they move with the flow of the water. In addition to plankton, fish also feed on other organisms that exist in aquatic environments, and these include nekton and benthos. The cultivation of these organisms is crucial to sustaining any aquaculture sector.

Part of pond aquaculture includes increasing plankton density. A total of three-fourths of the earth’s oxygen supply is produced by phytoplankton in the oceans. Phytoplankton helps increase the oxygen levels in water and is a major source of dissolved oxygen in pond photosynthesis. Plankton is also crucial to high altitude fish farming.

The words nekton and benthos are used to denote, small burrowing organisms, including creepers that occupy the bottom of water bodies or water expanses. They include crabs, amphipods, tendepeds, some bivelves, and certain types of fish, worms and crustaceans, all of which are an important source of nourishment for fish.  

Ideally hatchlings should feed solely on plankton. In the initial or early stages fish larvae do not react to dry feeds and require life feeds that swim actively and stimulate their raptorial behavior. Larval fish usually do not ingest or are not able to digest formulated feeds.

Plankton is divided into two components; the plant component is called phytoplankton and the animal component is called zooplankton. The larvae of most species of fish can feed exclusively on zooplankton or a combination of plant and animal plankton.

The growth of phytoplankton is stimulated in pond aquaculture by using the sun’s heat and light. Inorganic matter and carbonic acid are transformed into organic matter in the form of vegetable tissues.

In addition to providing sustainable nourishment for fish and maintaining the oxygen levels in water, plankton also helps stabilize pond water quality by balancing PH levels. Most studies indicate that phytoplankton and pond algae are just as vulnerable to toxins or pollutants in water, like chlorine, as are fish and zooplankton. 

Pollutants can, therefore, affect photosynthesis and other aspects of energy utilization and incorporation and, thus cause changes in population growth rates. Such changes are most easily seen in systems populated by algal and plant nutrients.    

Plankton is critical to breeding healthy cold water and warm water stocks and it is essential in both normal aquaculture and high-altitude aquaculture. Light is the main ingredient in cultivating plankton and it can be cultured in tanks like how spirulina is cultured but the tanks need to operate without water filters. Filtering will hamper the growth of cultured species.

In warm water environments there is a species of fish that can be used to remove the dirt or fish waste that sinks to the bottom of fish-tanks. The fish is called plecostomus or as it is more commonly known, the sucker mouth catfish. It lives at the bottom of tanks or on the floor of water bodies and feeds off dirt and other residue that sink to the base. The fish cohabits well with other breeds like carps and it is suitable for use in warm water aquaculture.

Plecostomus is an aggressive species and as the fish increases in size, it may have to be removed. Normally it is customary to have a small plecostomus for tank cleaning purposes and once the fish grows to a certain size, release it back into the wild or abandoned ponds.     

Plankton also helps reduce or minimize pathogenic and the unwanted microbial content in water by competing for available nutrients and this is critical because it reduces the need for water treatment and limits the use of antimicrobials or antibiotics.

Fish thrive best in natural environments and therefore where possible it is best to emulate or reproduce the salient features of its natural habitat.

The long-term use of plankton further reduces the percentage of cannibalism or fish consuming other fish. Phytoplankton ensures adequate oxygen levels in water and zooplankton and benthos ensure that fish are adequately or sufficiently nourished. Sometimes feeder fish (a term used to define inexpensive fish that are used to feed carnivorous pets) or tadpoles are used to feed symbiotically cultivated species. The use of feeder fish and tadpoles however is somewhat controversial and has drawn criticism from fish keeping hobbyists around the world.

The most common type of feed that is used in aquaculture is dry feed i.e. little pellets that float on the surface of the water, like plankton. One of the advantages of using dry feed is that it is produced to ensure optimum growth and maximize nutrients. It is also cheap and easy to use and there is some uniformity with quality but it does contaminate the water and the water has to be continuously recycled.     

Copyright © 2019 by Dyarne Jessica Ward and Kathiresan Ramachanderam