Eyestalk ablation

rdf:langString Eyestalk ablation

rdf:langString Eyestalk ablation is the removal of one (unilateral) or both (bilateral) eyestalks from a crustacean. It is routinely practiced on female shrimps (or female prawns) in almost every marine shrimp maturation or reproduction facility in the world, both research and commercial. The aim of ablation under these circumstances is to stimulate the female shrimp to develop mature ovaries and spawn. Most captive conditions for shrimp cause inhibitions in females that prevent them from developing mature ovaries. Even in conditions where a given species will develop ovaries and spawn in captivity, use of eyestalk ablation increases total egg production and increases the percentage of females in a given population that will participate in reproduction. Once females have been subjected to eyestalk ablation, complete ovarian development often ensues within as little as 3 to 10 days. The practice was a major development for the commercialisation of shrimp farming in the 1970s and 80s since it enabled reliable production. The most commonly accepted theory of why eye ablation reduces this inhibition is that a gonad inhibitory hormone (GIH) is produced in the neurosecretory complexes in the eyestalk. This hormone occurs in nature in the non-breeding season and is absent or present only in low concentrations during the breeding season. The reluctance of most shrimp to routinely develop mature ovaries in captivity is a function of elevated levels of GIH, and eyestalk ablation lowers the high haemolymph titer of GIH. The effect of eyestalk ablation is not on a single hormone such as GIH, but rather affects several physiological processes. Besides the GIH evidence, another hypothesis suggests that eyestalk ablation also reduces light perception intensity and thereby induces ovarian maturation. In the (Fenneropenaeus merguiensis, syn. Penaeus merguiensis), dim light favours ovarian maturation and spawning. The exact mechanism of eyestalk ablation on the ovarian maturation is not conclusive. The practice has been criticised by animal rights activists since the removal is often done without anaesthesia and the impaired vision leads to more stress for the animals. It has been reported that in the tiger prawn (Penaeus monodon), the eyestalks fully regenerate in less than six months.