Regulation of growth in turbot (Scophthalmus maximus Rafinesque) and Atlantic halibut (Hippoglossus hippoglossus L.): aspects of environment × genotype interactions
This review is aimed atelucidating the mechanisms that regulate growthin cultured juvenile Atlantic halibut (Hippoglossus hippoglossus) and turbot (Scophthalmus maximus) by evaluating thesignificance of environmental factors(temperature, photoperiod) and the interactionsbetween them. In addition, we examine growthproperties in three populations of juvenilehalibut and turbot in order to elucidate anygeographical differences in growth and growthefficiency in these species. Both temperatureand photoperiod have a significant andpersistent effect on growth rate in bothspecies. Temperature tolerance, demonstrated bya wide temperature range supporting maximalgrowth, increased with size. Fish subjected tocontinuous light exhibited faster growth thanthose experiencing a natural photoperiod or aconstant short day. Moreover, when thephotoperiod increased naturally with day-lengthor when fish were abruptly switched from beingreared on short-day conditions to continuouslight, a subsequent increase in growth rate wasobserved. This growth enhancing effect ofextended photoperiods was more apparent in ashort time scale in Atlantic halibut than inturbot, but both species show significantlong-term effects of extended photoperiods.
Enhanced growth in fish in continuous light waspartly explained by higher growth efficiency.In both species, there was a significantinteraction between temperature andphotoperiod, suggesting that thegrowth-enhancing effect of continuous light isrelatively stronger at lower temperatures.Growth rate in both species was alsosignificantly influenced by the interaction oftemperature and fish size, as the optimaltemperature for growth decreased rapidly withincreasing fish size. Differences in growth,food intake, food conversion efficiency,metabolism, ammonia excretion and RNA/DNAratios in white muscle were observed betweendifferent strains of halibut and turbot, withthe best growth properties being observed inthe northern populations. These findings onhalibut and turbot partly support the theory ofcountergradient variation in growth, suggestingthat populations from high latitudes havehigher growth capacity than populations fromlow latitudes.
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