Experimental design
We used a highly inbred (at least 20 generations of inbreeding) strain of K. marmoratus (R (Ellisonet al. 2012a)) kept under standard laboratory conditions (25-27 °C, 16-18‰, 12h light: 12h dark photoperiod). For the parental generation, eggs from five fish of similar size and age were reared individually until hatching, when larvae were transferred to tanks with either enriched environment (shelter and plants, n=14) or poor environment (identical except no enrichment, n=13), where they were kept for 10 months (Berbel-Filho et al.2019).
To standardise potential age-related parental effects, eggs were only collected from parents of similar age (7-10 months). The offspring of five genetically inbred parents (three from enriched and two from poor environments) were set up following a factorial design with matched or mismatched parent-offspring environments (Fig. S1; Table S1). The offspring consisted of 15 mismatched individuals (seven poor to enriched and eight enriched to poor), and 13 matched individuals (eight enriched to enriched and seven poor to poor).