Preservation of inherent contractility in isolated gut segments from herbivorous and carnivorous marine fish

Patterns of inherent contractility were investigated in isolated gut segments from three species of New Zealand temperate-water labroid fish: the herbivorous butterfish Grins pullus (Family Odacidae), and the carnivorous banded wrasse Notolabrus fucicola and spotty Notolabrus celidotus (Family Labridae). To maintain the functional viability of gut tissue over extended periods, physiological solutions were formulated for each genus based on biochemical analyses of plasma constituents. A Res-Del perfusion system was used to maintain isolated gut segments under conditions of constant pH, temperature, and laminar flow dynamics. Gut segments exhibited spontaneous contractility over periods of days. Segments from N. fucicola and N. celidotus were continuously active, whereas segments from O. pullus showed discontinuous activity with evidence of daily rhythmicity. Contractions were slight in segments from O. pullus compared to the two Notolabrus species. Contractile strength correlated with gut morphology, with circular and longitudinal muscle layers markedly greater in extent in the Notolabrus species than in O. pullus. The pattern of gut activity in O. pullus is possibly associated with the retention of algal material in the intestine for lengthy periods. This hypothesis is supported by the daily feeding pattern of this species, and the probable involvement of fermentation in its digestive process.