Morphological changes of pyloric caeca and their relevancy to motility in laboratory-reared Kurosoi rockfish (Sebastes schlegelii Hilgendorf), using an in vitro assay method

Abstract Artificial diets affect the growth and gut morphology of carnivorous fishes. In this study, we compared a laboratory raised rockfish, Sebastes schlegelii (a carnivore), fed an artificial diet (Lab fish), and the wild-captured rockfish (Wild fish) to confirm the effect of an artificial diet on pyloric caecal morphology and motility. We also established an in vitro method to quantify pyloric caecal sac motility and compared it between Lab and Wild fish. The pyloric caecal length per unit body length, the pyloric caecal weight per unit body weight, and the pyloric caecal weight per length were significantly greater in the Wild fish than in the Lab fish. Additionally, both of the circular and longitudinal muscularis layers were significantly thicker in the Wild fish than in the Lab fish. The pyloric caecal motor frequency of the Wild fish was higher than that in the Lab fish, but the contractile pressure of the pyloric caeca did not change under conventional conditions. These results suggest that the thickness of the tunica muscularis of the pyloric caeca may be involved in its motility, and the pyloric caeca of the Lab fish may not be able to provide functionality in this respect. In conclusion, under artificial rearing conditions, the artificial diet reduced the thickness of the tunica muscularis and reduced the motor frequency of the pyloric caeca in rockfish.