Abstract
Mandarin fish refuse dead prey fish or artificial diets and can be trained to transform their inborn feeding habit. To investigate the effect of memory on feeding habit transformation, we compared the reaction time to dead prey fish and the success rate of feeding habit transformation to dead prey fish with training of mandarin fish in the 1st experimental group (trained once) and the 2nd experimental group (trained twice). The mandarin fish in the 2nd group had higher success rate of feeding habit transformation (100%) than those in the 1st group (67%), and shorter reaction time to dead prey fish (<1 s) than those in the 1st group (>1 s). Gene expression of cAMP responsive element binding protein I (Creb I), brain-derived neurotrophic factor (Bdnf), CCAAT enhancer binding protein delta (C/EBPD), fos-related antigen 2 (Fra2), and proto-oncogenes c-fos (c-fos) involved in long-term memory formation were significantly increased in the 2nd group after repeated training, and taste 1 receptor member 1 (T1R1), involved in feeding habit formation, was significantly increased in brains of the 2nd group after repeated training. DNA methylation levels at five candidate CpG (cytosine–guanine) sites contained in the predicted CpG island in the 5′-flanking region of T1R1 were significantly decreased in brains of the 2nd group compared with that of the 1st group. These results indicated that the repeated training can improve the feeding habit transformation through the memory formation of accepting dead prey fish. DNA methylation of the T1R1 might be a regulatory factor for feeding habit transformation from live prey fish to dead prey fish in mandarin fish.
Highlights
Animal feeding habits and feed-preferences affect growth characteristics and living habits, and determine the aquaculture production costs and economic benefits
We examined the mRNA expression of genes involved in synaptic plasticity as well as memory formation in mandarin fish with the feeding habit transformation
Our results suggest that the increased expression of brain-derived neurotrophic factor (Bdnf), CCAAT enhancer binding protein delta (C/EBPD), and fos-related antigen 2 (Fra2) genes can compensate for zif268 down-regulation, and the significantly increased expressions of Bdnf, C/EBPD, and Fra2 genes of mandarin fish during the second training session might play important roles in memory consolidation of accepting dead prey fish
Summary
Animal feeding habits and feed-preferences affect growth characteristics and living habits, and determine the aquaculture production costs and economic benefits. Once the fry of mandarin fish start feeding, they only accept live prey fish in the wild and refuse dead prey fish or artificial diets [1,2] They can be trained to transform their innate feeding habit to accept dead prey fish [3]. We still do not know whether learning and memory can play an important role on feeding habit transformation. The behavioral parameters, expression of genes involved in learning and memory, and DNA methylation levels in the CpGs of the T1R1 gene involved in feed identification were examined in mandarin fish. This study improves the understanding of molecular mechanisms of learning and memory and the epigenetic regulation during the unique feeding habit transformation in mandarin fish
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