The oyster industry

The oyster industry has traditionally relied upon spat collection in the field to supply its needs for farm requirements. As the industry has expanded the need for a more predictable source of the spat has emerged. Likewise, the thought of controlling some desirable characteristics of the oysters has resulted in the set-up of hatchery and nursery facilities. The hatchery and nursery will give the farmer a predictable supply of spat and will allow greater manipulation of genetic traits, such as triploidy.

Today, triploidy is the most common method used to genetically improve marine bivalve aquaculture production. The hatchery and nursery facilities have exceptional water quality and hygiene which allows them to sustain healthy broodstock, induce spawning and maintain larval cultures.

Commercially, spawning is induced by chemical methods. These include different concentrations of hydrogen peroxide either in normal seawater or alkaline seawater (pH 9.1). The pH media can be prepared using Tris buffer or sodium hydroxide pellets. Injection of ammonium hydroxide (NH4OH) solution into the adductor muscle of the oyster also results in spawning. Serotonin-induced spawning, such as is used with giant clams can also be used on oysters. However serotonin is an expensive hormone and therefore its use in aquaculture farming would not be viable for the industry. A synthetic or recombinant fragment of the oyster pheromone could also be used in the aquaculture industry to induce spawning.

Pheromones play a critical role in triggering spawning in oysters. Male and female oysters are stimulated to spawn by oyster sperm. Male oysters are also stimulated to spawn by oyster eggs, but females are not. The oyster sperm pheromone is a heat and trypsin sensitive intrinsic membrane protein. Naturally in summer, oyster spawning is triggered by elevated temperature. This triggers a stress response as energy is being expended on adapting and overcoming the stressful stimuli. This ultimately results in oysters releasing their gametes into the water column. Therefore we are going to use thermal shock to demonstrate induction of spawning. It should be noted that this is not commercial practise, as it stresses the animal and also alters the water quality by depleting available oxygen and changing pH levels in the aquaculture tanks.