Flounder with partial intestine osmoregulate in seawater

Abstract

Summer flounder (Paralichthys dentatus) that survived flounder infectious necrotizing enteritis (FINE) provided an unusual model for testing the role of the intestine in maintaining salt and water balance. The survivors lost 67% of the posterior-most intestine. The remaining stump of the anterior intestine healed and became a blind pouch. We sampled the fish three months after the epizootic ended, demonstrating that these fish survive with only a portion of their intestine. We hypothesized that salt and water balance would be disturbed in the survivors of FINE. However, plasma osmolality and concentrations of Na⁺, Cl⁻, and K⁺ were the same in intact flounder and those with only an intestinal stump. No compensatory changes in gill Na⁺, K⁺-ATPase activity were detected. The fish with intestinal stumps continued to feed, but their body weight was only 41% that of intact fish. Summer flounder can maintain salt and water homeostasis, but fail to thrive, using only one-third of their intestine.