Fish density, but not environmental enrichment, affects the size of cerebellum in the brain of juvenile hatchery-reared Atlantic salmon

Joacim Näslund,Jörgen I Johnsson,Malin Rosengren

doi:10.1007/s10641-019-00864-9

Joacim Näslund, Jörgen I Johnsson + Show 1 more

Open Access

https://doi.org/10.1007/s10641-019-00864-9

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Abstract

This paper describes a study on the environmentally dependent brain size plasticity in hatchery-reared Atlantic salmon Salmo salar L. Using a factorial experimental design, we tested whether tank fish density, local hatchery standard (150 fish ∙ m−2) vs. reduced (50 fish ∙ m−2) and structural enrichment, a bundle of submerged plastic stripes, had effects on the size of the cerebellar region of the brain. Fish reared at reduced density had smaller cerebella, while structural enrichment had no detectable effects. The density effect on cerebellum, which is involved in locomotion and cognition, confirms previous results from hatchery-reared Atlantic salmon. The lack of detectable positive effects of enrichment, which contrasts some previous studies, provide further evidence for a complex relationship between environmental complexity and brain growth.

Highlights

Stocking of juvenile hatchery-reared fish is a common, and controversial, practice (e.g. Lorenzen 2014; Stewart et al 2015)
We investigated the size of cerebellum in hatchery-reared Atlantic salmon reared at high or low (1/3 of local hatchery standard) density, in presence or absence of structural enrichment
No indication of cerebellum size being associated with smolt status was found (Pearson r = 0.042, p = 0.78)

Summary

Introduction

Stocking of juvenile hatchery-reared fish is a common, and controversial, practice (e.g. Lorenzen 2014; Stewart et al 2015). Stocking of juvenile hatchery-reared fish is a common, and controversial, practice Survival of stocked fish is commonly less than half of that of wild conspecifics with the same genetic origin (Jonsson and Jonsson 2011), with most of the mortality occurring very soon after release In some cases the post-release performance of hatchery-reared fish is similar to that of wild conspecifics, which suggests that hatchery rearing practices can be adapted to produce wellperforming stock fish (Araki and Schmid 2010). Hatchery rearing has been known to produce fish with different characteristics than wild fish for at least a century, and this is a likely cause of the poor wild performance

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