Environmental enrichment influence on physiology and behaviour
Structural environmental enrichment has been used in captive fish as an
attenuator of maladaptive or aberrant traits
(Näslund & Johnsson 2016;
Roberts et al. 2014;
Roberts et al. 2011). Shelter-like
structures (e. g. perforated logs, pipes) have generally beneficial
effects, such as decreased metabolic rates
(Fischer 2000;
Millidine et al. 2006) and reduced
plasma cortisol levels (Näslund et
al. 2013), particularly in aggressive species
(Näslund et al. 2013). Our results
indicate that parental fish reared on enriched environments have lower
basal metabolic rates and waterborne cortisol levels. While metabolic
rate did not appear related to the rearing environment of the parents,
the tight correlation between waterborne cortisol levels and basal
metabolic rates in parental fish, suggests that parental individuals
reared in enriched environments were less stressed and spent less energy
to maintain basal metabolic rate than individuals reared in barren
environments.
In fish, structural environmental
enrichment tends to decrease activity, mainly due to increased
sheltering (Moberg et al. 2011;
Roberts et al. 2011;
von Krogh et al. 2010), and
exploratory activity and boldness tend to be positively correlated
(Champneys et al. 2018;
Mazué et al. 2015). Here, parents
reared on enriched environments were slightly more active, but also more
neophobic, than individuals reared in poor environments, suggesting no
clear boldness-exploratory relationship in response to environmental
enrichment in K. mamoratus . In this sense, plastic behavioural
responses during the ontogeny of this species have been previously
suggested, based on its variable responses to conspecific presence and
simulated predation risk (2013).
Although behavioural effects of environmental enrichment on fish are
well known (Jonsson & Jonsson 2014;
Näslund & Johnsson 2016), the
understanding of their potential inter- or transgenerational effects is
limited, as most studies have focused on one generation
(Näslund & Johnsson 2016). Our results
indicate that offspring activity and neophobia were influenced by the
parental rearing environment. In general, offspring from parents reared
in enriched environments had higher activity levels, regardless of their
own environment, suggesting a sustained parental effect on activity
levels. Previous studies in this species suggested that life-history
traits (offspring size), but not behaviour (exploration, boldness and
aggression), were affected by the parental environment
(2013). However, in mammals there is
ample evidence of parental effects caused by environmental enrichment,
where the offspring from enriched environments tend to be more
exploratory (Dell & Rose 1987;
Mychasiuk et al. 2012), have
increased learning capacity and memory formation
(Bygren 2013), than those reared in
non-enriched environments. While in fish increased cognitive capacity
due to environmental enrichment was known
(Roberts et al. 2011;
Salvanes et al. 2013), this is the
first evidence of behavioural intergenerational (parental) effects.