Course Content
Learn Principles of Aquaculture with Rahul

Introduction

  • Fish are cold-blooded aquatic vertebrates which breathe by means of pharyngeal gills and propelling and balancing themselves by means of fins which are supported by dermal fin rays.

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General characteristics of fishes

  • Are aquatic, cold-blooded vertebrates.
  • Body is generally fusiform and streamlined but in globiformes ( eg Puffer fish), the body is globe shape and in eels is of serpentine form. The ground plan of the body is bilateral symmetrical with prominent lateral line system in spite of variations in shape.
  • Body is covered by tough skins armored by variety of scales.
  • Appendages of fish comprise of the fins which are generally paired ( Pectoral and pelvic fins) and unpaired ( dorsal, anal and caudal fins). All fins are supported by dermal rays. These fins are the main locomotory organ.
  • Mouth generally situated anteriorly in the head and the anus is in the second half of the overall length of the individual behind the bases of the pelvic fins and just in front of the anal fin.
  • Jaws are hinged.
  • Respiratory organ is generally in the form of gills and other accessory respiratory organs.
  • Nostrils are paired but don’t open into the pharynx, except in lung-fishes and lobed-fishes.
  • Skeleton of the fishes is in the form of notochord, connective tissues, bones, cartilages and non-bony scales.
  • The digestive tract is complete.
  • Heart is 2 chambered with single auricle and ventricle.
  • Kidneys are paired, longitudinal structures that lies above the body cavity.
  • Brain is well developed with ten pairs of cranial nerves.
  • Cranium completely surrounds the brain.
  • Middle ear is completely absent but internal ear with well-developed semi-circular canals.
  • Sexes are separate.
  • Mostly oviparous ( egg laying) but some are viviparous ( direct birth giving).
  • Fertilization is generally external.
  • Embryonic membranes are absent.
  • Eggs are large with much yolk.
  • Development is direct ( without any metamorphosis).