Most problems with fish health are related to water quality. Fish necropsy may be conducted to eludicate the cause of fish death. The cause of fish death may be chemical, biological, physical or any combination of these.

Fish anatomy presents a colorful sketch of the fish seen from its left profile. Four poles of the fish are depicted as upper, dorsally one; lower, ventrally one, anteriorly, left one, and posteriorly, right one. Some of the internal organs are marked, together with their names - brain, gills, kidney, heart, esophagus, liver, stomach, intestine, pancreas, reproductive organ, anus, bladder, swim bladder and gallbladder. Also, five fish fins are marked - pelvic fin at the bottom front, anal fin at the bottom back, spiny forsal fin at the upper front, soft dorsal fin at the upper back, and caudal fin at the back of the fish. The spinal cord and lateral line is also marked, stretching through the whole side of the fish, from the head to the caudal fin.

These broad categories include:

  • Oxygen related (anoxia, hypoxia, winter kill, algal blooms)

Oxygen levels in the water can drop below the level needed to support life. In low oxygen levels, physostomous fishes will try to survive by gulping air at the water surface. The size of the affected fish is significant. A fish kill caused by depressed oxygen levels will not include smaller fish unless critically low concentrations are reached.

  • Trauma related (fishermen, predation, explosive shock, turbine effect)

Trauma related to explosions can cause detrimental effects not only to the fish, but also to the ecosystem. Surrounding habitats, such as coral reefs, are often damaged by explosions.

  • Toxins or poor water quality (industrial or domestic pollution, pesticides, fertilizers, oil, rapid thermal shift, changes in salinity, toxic algae)

  • Disease or population pressure (viral, bacterial, fungal, parasitic, spawning stress, over population)