Fish use spatial cognition based on allocentric cues to navigate, but little is known about how environmental enrichment (EE) and exercise affect learning and memory in correlation with hematological changes or gene expression in the fish brain.
More...Fish use spatial cognition based on allocentric cues to navigate, but little is known about how environmental enrichment (EE) and exercise affect learning and memory in correlation with hematological changes or gene expression in the fish brain. Here we investigated these questions in Colossoma macropomum (Teleostei). Fish were housed for 192 days in either EE or an impoverished environment (IE) aquarium. EE contained toys, natural plants, and a 12-hour/day water stream for voluntary exercise, whereas IE had no toys, plants, or water stream. A third plus maze aquarium was used for spatial and object recognition tests. Compared with IE, the EE fish showed greater learning rates, body length, and body weight. After behavioral tests, whole brain tissue was taken, stored in RNA-later, and then homogenized for DNA sequencing after conversion of isolated RNA. To compare read mapping and gene expression profiles across libraries for neurotranscriptome differential expression, we mapped RNA-seq reads to the C. macropomum whole genome assembly. The results showed significant differential counts and gene expression. The total number of estimated telencephalic cells was greater in EE than in IE animals, but without significant differences in the tectum opticum. A total of 107,669 transcripts were reconstructed that ultimately yielded 64 differentially expressed genes between IE and EE brains. Another set of adult fish kept in aquaculture conditions were either subjected to physical exercise using water flow or kept sedentary. Flow cytometry analysis of peripheral blood showed a significantly higher density of thrombocytes, granulocytes, erythrocytes, and lymphocytes in the exercised group compared with the sedentary group. Thus, under the influence of contrasting environments, our findings showed differential changes at the behavioral, cellular, and molecular levels. We propose that the differential expression of selected transcripts, number of cell counts, learning and memory performance, and selective hematological cell changes may be part of Teleostei adaptive physiological responses triggered by EE visuospatial and somatomotor stimulation. Our findings suggest abundant differential gene expression changes depending on environment and provide a basis for exploring gene regulation mechanisms under EE in C. macropomum.
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