Early life history of daubed shanny (Teleostei: Leptoclinus maculatus) in Svalbard waters

Abstract

The daubed shanny (Leptoclinus maculatus, Family Stichaeidae) is considered to be an ecologically significant species in the arctic waters of Norway because of high abundance and the unique energy storage abilities of its postlarvae. Both postlarvae and adults are found in relative large abundances in Svalbard fjords as well as along the ice edge of north-east Svalbard, even at sub-zero temperatures. The postlarva feeds primarily on Calanus spp. and stores lipids from this high-energy diet in a unique lipid sac on the ventral side of its body. This energy storage enables it to survive pelagically during the arctic winters when food is scarce. The postlarvae are pelagic for the first 2–3 years of their life before they descend to the bottom and transform to a benthic mode of life. Our results indicated that this transition takes place when the postlarva reach about 80 mm in length and an age of 3 years. The relative size of the lipid sac, as well as changes in the morphology of the postlarvae, can be used as indices of the transition from pelagic postlarva to benthic juvenile. The lipid sac index (% of gutted weight) was negatively correlated with length and age and started to decrease when the postlarva transformed to a benthic lifestyle. At this point, the growth in terms of the length–weight relationship shifted from a positive asymptotic growth to a negative asymptotic growth, reflecting the changes in the lipid sac index, while several changes in morphological traits took place. The benthic mode of early juveniles is largely influenced by environmental conditions and prey abundance, since the fish is depleted from their energy stores and need to rapidly switch to benthic prey in their new habitat. In conclusion, this is the first study on the early life history of the daubed shanny and it presents evidence that the first 5 years in the life of this species is divided in two distinct parts, one pelagic and one benthic, in which postlarvae display unique growth and morphological traits adapted to the challenges of these arctic marine environments.