A UK perspective on intensive hatchery rearing methods for Atlantic halibut (Hippoglossus hippoglossus L.)

A review is presented of UK hatchery rearing techniques for Atlantic halibut (Hippoglossus L.), based on research findings and commercial practices. Operations from gamete collection through to weaning are covered, including reference to survival rates at each developmental phase. Areas of recent progress are discussed in relation to the remaining production bottlenecks and research requirements. Rearing techniques have been shaped to a large extent by the temperate water conditions prevailing at UK hatcheries. The requirement of halibut broodstock and eggs/yolk sac larvae for cold, stable water conditions has placed an emphasis on intensive hatchery systems that incorporate accurate temperature control mechanisms. The energy costs associated with chilling are reduced by the use of low water flow rates and water recycling, where possible. Yolk sac larvae are reared in smaller tanks (500-2000 l volume) than conventional Norwegian-style 'silos'. Configuration and husbandry procedures for this developmental stage have been modified accordingly, including early transfer of the yolk sac larvae to feeding tanks (at around 150-180 degree days post-hatch). The live feeding phase is mostly carried out indoors under artificial lighting. Feeding is typically initiated at an age of 220-250 degree days post-hatch. Brine shrimp, Artemia sp., constitute the basis of the diet in most cases, with the exception of one commercial hatchery engaged in large scale copepod production. Recent research on this phase has focused on defining Artemia enrichment protocols and methods of diet presentation, with the aim of improving the survival and growth rates of larvae, and their metamorphosis attributes. Crumbled feeds are used to wean halibut juveniles onto formulated diets. Recent improvements in hatchery survival rates, combined with greater egg availability, have enabled UK production capacity to rise to hundreds-of-thousands of juveniles per year using existing commercial facilities. Operators have identified the transition from late yolk sac phase to onset of feeding as the primary hurdle remaining in the hatchery rearing process and this is the subject of ongoing research into physical environmental conditions, handling methods and microbial conditions in the rearing tanks.