Anesthesia is a state caused by an applied external agent resulting in a loss of sensation through depression of the nervous system. The use of anesthetics in fisheries and aquaculture research greatly facilitates in procedures including induction of breeding, handling during stripping and transport of broodstock. Anesthesia and sedation is usually essential to minimize stress and physical damage in handling the fish for routine operations . Although the use of anesthetics is primarily for the purpose of holding fish immobile while the animal is being handled for sampling, anesthetics are also used to lower the level of stress associated with such procedures.
When choosing an anesthetic a number of considerations are important such as its efficacy, cost, availability, ease of use and side effects on fish, humans and the environment. Overdosing of an anesthetic or retaining the fish in an anesthetic bath for too long leads to the fading of ventilation, hypoxia, and finally, respiratory and cardiac collapse . A wide variety of compounds have been utilized to anesthetize fish during artificial propagation techniques. The use of anesthetics in fish has spanned more than the last five decades and many chemicals (MS-222, benzocaine, quinaldine, chlorobutanol, phenoxyethanol, metomidate etc.) have been employed in fresh water fishes. Stages of anesthetization included induction, maintenance and recovery.