Overviews on Diversity of Fish

摘要

Fish have great diversity and hence they can be classified in different categories. "Fish" generally refer to several aquatic animals but actually all of them are not fish, such as starfish, shellfish, cuttlefish, jellyfish and crayfish. Jawlesh fish are the most primitive fish. In deed, the ancestors of cartilaginous fish (having a cartilaginous skeleton) were the bony animals and they developed paired fins firstly. Bony fish are categorized into the lobe finned and ray finned fish. Teleost fish are the most 'modern' (advance). As regard to size, Paedocypris progenetica is the smallest fish. Gobies have the shortest life span and they are small coral reef-dwelling fish. Only 58% of extant fish are salt water, while a disproportionate 41% are fresh water fish and remaining 1% is anadromous fish. Groupers are protogynous hermaphrodites, who school in harems of 3 to 15 females. Fish adopt a variety of strategy for nurturing their brood, e.g., shark differently adopts three protocols with brood. Many fishes are food opportunists or generalists as they eat whatever they get easily. Fishes with four eyes have eyes above the top of head which are divided in two different parts, so that the fish can see below and above the water surface simultaneously. Seahorses are the slowest-moving fishes. So called the 'toxic fishes' are able to produce strong toxins in their bodies. Moreover, there are commercial food fish, recreational sport fish, decorative aquarium fish and tourism fish. As the most vertebrate species have brain-to-body weight ratios, fish also have the relative brain weights of vertebrates.