The effect of ozonation on the survival, growth and microbiology of the European lobster (Homarus gammarus)

The fishery for the European lobster, Homarus gammarus has declined in recent years and has subsequently impacted on local socio-economics and ecology at wider scales. This has led to the formation of hatcheries (restocking wild populations with juveniles) and more recently, an interest in land based farms (ongrowing of juveniles to an edible size for direct consumption). To optimise the success of lobster rearing, ozone was investigated as a sustainable, scalable antibacterial treatment to assist water quality management and hence survival of captive lobsters at larval and post larval (PL) stages. Larval lobsters were exposed to constant ozone at a candidate concentration (400 mV, ca. 15 ppb) in a number of replicate upwelling hopper systems in five repeated experiments. At intermediate sampling points during larval rearing, ozone treatment resulted in significantly enhanced survival while Vibrio sp. bacterial load was significantly reduced in ozone treated larvae and culture water compared to controls. However, larval length and weight declined towards the end of the five repeated 18 day trials, potentially due to the effects of ozone on water chemistry and hence larval nutrition and physiology. To understand if ozonation had longer term effects on PL after metamorphosis, groups of ozonated and unozonated larval recruits were placed in separate control and constantly ozonated raceways to create four treatments. Ozone did not reduce growth rate in PL exposed to ozone at any life stage. With both “double” treatments, survival was similar and approximately average considering all four treatments, was elevated in lobsters ozonated as PL only and reduced in lobsters ozonated as larvae only.

► Lobsters were resilient to direct application of 400 ppm ozone over several months.
► Vibrio sp. decreased in ozonated water and larvae compared to unozonated controls.
► Larval survival increased, but length and weight were reduced in ozonated systems.
► Post larvae (PL) did not show a clear trend in growth or survival.
► Strategic ozonation regimes could assist hatcheries by improving recruitment to PL.