Types And Methods Of Fish

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2.1 General: A fish is any member of a paraphyletic (descendants of the last common ancestor)group of organisms that consist of all gill bearing aquatic craniate animals that lack limbs with digits (fingers and toes). Fish are an important resource for humans worldwide, especially as food. Commercial and subsistence fishers hunt fish in wild fisheries or farm them in ponds or in cages in the ocean. They are also caught by recreational fishers, kept as pets, raised by fish keepers, and exhibited in public aquaria. 2.2 Fish behaviour and migration: Rheoreaction, which is an inherent behavioural response of fish to swim upstream, underlies fish behaviour in the flow (Fig. 2.1). All other features of behaviour in the stream have to be seen against a background of this particular reation. Rheoreaction has two components of behaviour: orientational and locomotor. Organs of vision, touch, equilibrium (horizontal labyrinth channels) and neuromast help fish find its way against the current. Locomotor activity of fish in the stream can be described by several functional indices: threshold flow rate (its value sets the lower limit of flow rate for fish rheoreaction to develop), critical flow velocity (its value defines the upper limit of velocity interval, within which fish retention in the stream is possible), burst speed and swimming capacity (duration of fish motion at different flow velocities). [1] Fish populations are highly dependent upon the characteristics of the aquatic

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