Plankton and fisheries

Plankton and fisheries

1. Plankton and Fisheries

2. What exactly are plankton? Plankton are weakly swimming or drifting organisms “ Plankton ” is not a single species but a large group of organisms that fall into two primary categories: Phytoplankton (plants) Zooplankton (animals) 3. Many are microscopic, some visible to the naked eye

3. Why are plankton important? Important part of global carbon cycle Food source (basis of the food web) Producer of oxygen (photosynthesis)

4. Link in the food chain There are several other fishes and mammals in the sea whose life is linked with phytoplankton . Each species has its own period of growth and the growth intensity depends on many external factors such as temperature, salinity, nutrients and the physiological state. These factors are influenced by season and climate. The largest fish-the basking shark, is also a planktonic feeder, mainly feeding on the copepod Calanus which survives on the phytoplankton. The fishery for oil sardine and mackerel are entirely dependent on the bloom of phytoplankton along the west coast of India.

5. Fish Plankton Relationship The plankton occupies the first trophic level in the food chain and hence its contribution to the subsequent higher level of energy transfer is of great importance to the fishery biologist. Both herbivorous and carnivorous fishes do depend upon the plankton as their source of food and ultimately as their source of energy. The relationship between plankton and fish are manifold in the aquatic environment.

6. The remarkable relationship of plankton and fish Plankton as food of fishes Plankton as an index of fish abundance Mutual relationship Host parasitic relationship Plankton as a causative agent of fish mortality

7. Plankton as Food of Fishes Young stages of many bottom living fish feed on plankton. It is thus clear that their abundance and their distribution are directly linked to the plankton. Plankton is thus of fundamental important to the fisheries through a shorter or longer food chain according to the type of food the fish eat. Adult fish living on the bottom are also dependent on the plankton, not so directly as the larvae and the pelagic fish, Rotifers are of substantial importance to freshwater fishes. For many fishes, rotifers are the basic food in the earlier stage of life history. The crustaceans are one of the most important groups of plankton population in relation to fish particularly in respect of their food . Crustaceans are eaten largely by majority of fishes. The copepods, chiefly Calanus , constitute the main portion of food of herring. Although herring will take other foods when necessary, they prefer Calanus if available in sufficient quantity

8. Plankton As An Index Of Fish Abundance The region rich in nutrient usually develops a rich plankton population and many fishes accumulate there. Of particular importance to the life of fishes are phosphate and nitrate because the presence of these compounds particularly favors the development of organic lives in the water. It in noteworthy that the numbers of young of certain marine commercial fishes are in close dependence upon the zone of maximum plankton production. The adaptive nutritional significance of the shoal is most strongly expressed in pelagic shoaling fishes.

9. Mutual Relationship A t the time of photosynthesis, the phytoplankton uses co 2 and release o 2 . during respiration the fish use the o 2 and liberate co 2 which in turn can be utilized by the phytoplankton during photosynthesis. thus, both the organisms are benefited through the gas exchange between them . Sun Solar energy Autotrophs (primary producers) Plant/animal energy sources (carbohydrates) Heterotrophs (consumers)

10. Host – Parasite Relationship Many planktonic copepods act as intermediate hosts and help in the transmission of certain diseases of fishes. For example, the life cycle of Bass tapeworm could not be completed unless the eggs of the Proteocephalus ambloplitis are eaten by the copepod plankton. Again, this copepod plankton is eaten by the fish and thus the fish becomes infected with the disease

11. Plankton As A Causative Agent Of Fish Mortality The extensive literature dealing with the problem of sudden fish mortality reveals that the heavy bloom of phytoplankton may be responsible for the death of fish due to the reasons as follows: Accumulation and decay of thick algal population Secretion of toxic substances by phytoplankton Depletion of oxygen

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