PART1:- INTRODUCTION TO FISH

1.1. General concepts on fish

Fish
Fishes are aquatic cold-blooded vertebrates which breathe by means of gills and propelling and balancing themselves by means of fins that are supported by dermal fin rays. However, some species are well known for their ability to leap over the sea surface and fly long distances using their fins as wings. In addition, other species can live out of the water for short period, walk to migrate to other water bodies using accessory respiratory organs, and some species do not have scales on their body. The word fish is sometimes used more broadly to include any edible animal living in water. In this book, we limit to fish in the narrow sense which includes animals belong to only super-class ‘Pisces’. Fish are also called Pisces or Ichthys.

Fish or Fishes

The term ‘fish’ can be used boh as a singular or plural when talking about fish of the same species. For example, one salmon is a fish, three salmons are three fish. On the other hand, the word ‘fishes’ is usually used as the plural of fish when taking the multiple species of fish. For example, one salmon is a fish, but one salmon and one tilapia are two fishes.

Ichthyology
(GK: Ichthys or Ikhthus – fish; logos – study). Ichthyology is the branch of zoology devoted to the study of fishes. In simple words, the study of fishes is called Ichthyology. This includes bony fishes (Osteichthyes), cartilaginous fishes (Chondrichthyes), and jawless fishes (Agnatha).

Fish diversity
Fishes are the most diverse group of vertebrates, with more than one-half of the total vertebrate species. It is believed that fish began to evolve about 480 million years ago. They can be found in nearly all aquatic environments, from high mountain streams to the abyssal and even hadal depths of the deepest oceans. According to FishBase (2014), there are about 32,800 species of fishes, of which about 10,000 are freshwater fish. While a majority of species have probably been discovered and described, approximately 250 new species are officially described by science each year. These figures probably underestimate the exact numbers, as more species continue to be described. Thus, there may be well over 40,000 species of fishes worldwide. Out of total fishes, about 96% are bony species and rest are cartilaginous species. Many types of aquatic animals named ‘fish’, such as Shellfish, Crayfish, Jellyfish, Starfish, Cuttlefish, etc. are not a true fish. They, and some aquatic mammals like Whales, Dolphins and Pinnipeds (Seals and Walruses) are not a focus of Ichthyology. 

Fisheries
The industry or occupation devoted to the catching, processing and selling of aquatic organisms from natural water resources are the fisheries activities. According to FAO (1988), aquatic organisms, which are exploitable by the public as a common property resources with or without appropriate license are known as fishery. For example, Marine fisheries, Riverine fisheries, Lake fisheries, Reservoir fisheries, fishing on wetlands, etc. In general, the fisheries activities can be divided as capture fisheries, enhanced fisheries and culture fisheries or aquaculture.