Environmental rearing conditions produce forebrain differences in wild Chinook salmon Oncorhynchus tshawytscha

Abstract

Recent studies suggest that hatchery-reared fish can have smaller brain-to-body size ratios than wild fish. It is unclear, however, whether these differences are due to artificial selection or instead reflect differences in rearing environment during development. Here we explore how rearing conditions influence the development of two forebrain structures, the olfactory bulb and the telencephalon, in juvenile Chinook salmon (Oncorhynchus tshawytscha) spawned from wild-caught adults. First, we compared the sizes of the olfactory bulb and telencephalon between salmon reared in a wild stream vs. a conventional hatchery. We next compared the sizes of forebrain structures between fish reared in an enriched NATURES hatchery and fish reared in a conventional hatchery. All fish were size-matched and from the same genetic cohort. We found that olfactory bulb and telencephalon volumes relative to body size were significantly larger in wild fish compared to hatchery-reared fish. However, we found no differences between fish reared in enriched and conventional hatchery treatments. Our results suggest that significant differences in the volume of the olfactory bulb and telencephalon between hatchery and wild-reared fish can occur within a single generation.

Neuroendocrinology of sexual plasticity in teleost fishes

“…Working with brown trout ( Salmo trutta ), Kolm and colleagues [89] found that sneaker males had larger brains relative to their body size than migratory bourgeois males, although the cerebellum was relatively larger in the migratory morph. This brain difference is consistent with other studies demonstrating plasticity in salmonid brains [79,101]. As with the GnRH differences described between male phenotypes in bluehead wrasses in section 2, the HPG axis is important in differentiating parr from immature migratory males in Atlantic salmon with the maturing parr showing greater LHβ and FSHβ subunit mRNA levels in the pituitary, greater LH and FSH receptor mRNA in the testes, and greater testis size and 11KT levels.…”

Neuroanatomical relationships between FMRFamide-immunoreactive components of the nervus terminalis and the topology of olfactory bulbs in teleost fish

“…Several correlations have been found between the brain organization of fish and various ecological and behavioural patterns, such as diet and feeding habits (Huber et al 1997;Gonda et al 2009) and environmental and social factors (Lema et al 2005;Kihslinger et al 2006;Pollen et al 2007;Gonzalez-Voyer et al 2010;Kotrschal et al 2012;Lecchini et al 2014). Some of these factors might also explain the variability that we observed in the position of the OBs and the corresponding neuroanatomy of FMRFamide-ir NT components.…”

Environmental enrichment promotes neural plasticity and cognitive ability in fish

“…An indication of this comes from studying the brains and the behavioural repertoires of animals reared in captivity. Captive-bred animals generally have reduced behavioural diversity and less behavioural flexibility, and many regions of the brain are smaller and less active compared with wild counterparts [4][5][6][7]. Such reductions appear to be a by-product of the constant, non-demanding rearing environment [8,9].…”