Rearing environment affects spatial learning in juvenile Chinook salmonOncorhynchus tshawytscha

Abstract

We tested the prediction that a complex physical rearing environment would enhance short-term spatial memory as assessed by learning ability in a spatial navigation task in juvenile Chinook salmon Oncorhynchus tshawytscha. We reared fish in two low-density treatments, where fish were either in bare fiberglass tanks (bare) or in tanks with physical structure (complex). We also tested conventionally reared high-density hatchery fish to compare with these other experimental treatments.Our reason for including this third hatchery treatment is that the two low-density treatments, aside from the manipulation of structure, followed a rearing programme that is designed to produce fish with more wild-like characteristics. We tested individually marked fish for seven consecutive days and recorded movement and time to exit a testing maze. Stimulus conspecific fish outside the exit of the maze provided positive reinforcement for test fish. Fish from the bare treatment were less likely to exit the start box compared with fish in the complex and hatchery treatments. However, fish in the hatchery treatment were significantly more likely to exit the maze on their own compared with both the bare and complex treatments.Hatchery fish effectively learned the task as shown by a decrease in the number of mistakes over time, but the number of mistakes was significantly greater on the first day of trials. Increasing habitat complexity with structure may not necessarily promote spatial learning ability, but differences between hatchery and experimental treatments in rearing density and motivation to be near conspecifics likely led to observed behavioural differences. K E Y W O R D Scaptive-rearing, cognition, complex structure, density, environmental enrichment, hatchery

On the relevance of animal behavior to the management and conservation of fishes and fisheries

“…Ion regulatory ability is key and can be influenced by stress that could affect behavior (Stewart et al 2016(Stewart et al , 2017. Visual isolation, as a consequence of structure in an environment, could also affect how fish respond to stressors and hence behavior (Cogliati et al 2019b). Other studies explored how physiology is involved in fish social behavior (Noakes and Leatherland 1977).…”

Reared to become wild-like: addressing behavioral and cognitive deficits in cultured aquatic animals destined for stocking into natural environments—a critical review

“…Even though the assumption is common, there is surprisingly few studies demonstrating this, possibly because it is difficult to control for effects of previous experience when using wild individuals. However, several studies show cognitive differences between hatchery animals reared in different environments , Strand et al 2010, Salvanes et al 2013, Cogliati et al 2019, indicating that the rearing environment plays a part in cognition, at least in the short-term. Makino et al (2015) showed that learning ability of cultured striped knifejaws (Oplegnathus fasciatus) was inferior to wild conspecifics.…”

“…Increased spatial learning in maze trials have been detected in rainbow trout, with effects increasing along with increased enrichment-exposure time (Ahlbeck- Bergendahl et al 2016). Positive effects on spatial learning have also been seen in Atlantic salmon (Salvanes et al 2013), but not in brown trout or chinook salmon , Cogliati et al 2019. This variation in effects seen in salmonids puts the generality of effects of enrichment into question, and it would be useful to further investigate what causes these differences (species-specificity, types of enrichment structures, experimental design, or other factors).…”