Determining the optimum temperature and salinity for larval culture, and describing a culture protocol for the conservation aquaculture for European smelt Osmerus eperlanus (L.).

Populations of anadromous European smelt Osmerus eperlanus (L.) are declining across its geographical range in northern Europe, but no practical culture techniques exist to develop stock enhancement programmes for this species. In this study, a culture protocol is described to rear fish from fertilised eggs to mature adults in 2 years involving the use of 'green water', live feed and artificial diets. The sequence of embryonic development for eggs incubated at 10°C/0 ppt was described and photographed. To determine the optimum conditions for larval culture, fertilised eggs were reared at a range of salinities (0–20 ppt) and temperatures (5–18°C) until first feeding. Best hatching success (ca. 97%), size at hatch (ca. 0.8 mm) and survival to first feeding (ca. 96%) of larvae were achieved under combined conditions of low salinity (0–0 ppt) and temperature (5–10°C). No larvae survived a salinity of 20 ppt. The time taken from fertilisation to hatch (FtH) and hatching duration (HD) were temperature‐dependent ranging from 42 days FtH and 10 days HD at 5ºC, to 10 days FtH and 2 days HD at 18°C irrespective of salinity. The results indicate that conservation programmes could utilise existing salmonid hatchery facilities (i.e. freshwater, ≤10°C water temperature) for stock enhancement. Since on‐growing of smelt involves the logistical and technical problems of live feed production, it is recommended that smelt enhancement programme utilise freshwater hatchery facilities to rear fish until hatching, and then stock out onto known spawning grounds in rivers allowing hatched larvae to drift into estuaries to complete the larval and juvenile phases. This approach would minimise the time spent in the hatchery post‐hatching, eliminate the need for live food production, prevent the development of predator‐naïve fish, and hence would mimic the natural life cycle of the species as closely as possible. [ABSTRACT FROM AUTHOR]