WOURMS, J.P.: Evolutionary trends in gut and trophotaenia-based embryonic nutrition in viviparous teleosts.

Embryos of viviparous fishes acquire maternal nutrients via several routes. Enterotrophy involves the gut or gut derivatives. In the unspecialized state, nutrients imbibed from the ovarian fluid are absorbed in a simple, tubular gut. Resulting increases in embryonic weight range from slight to extensive, viz. Sebastes 20% (Scorpaenidae); Poeciliopsis 1840% (Poeciliidae), and Jenynsia, 24,000% (Anablepidae). Two adaptations for enterotrophy have evolved. First, the embryonic gut enlarges and its villi hypertrophy. Resulting increases in embryonic weight range from modest to very extensive, viz. Zoarces; 1100% (Zoarcidae); Embiotoca, 20,400% (Embiotocidae), and Anableps, 842,000% (Anablepidae). Trophotaeniae, the second adaptation, are gut-derived, external structures that surround the vent. They are best known in the Goodeidae (Cyprinodontiformes) where nutrient uptake produces weight increases from 2700% (Goodea) to 35,000% (Ameca). Paradoxically, Ataeniobius toweri, the only goodeid whose embryos lack trophotaeniae, seems as matrotrophic as Ameca, but relies on gut-based nutrition. Unspecialized gut-based nutrition can function at low concentration and variable supply but seems more efficient at high concentration and constant supply because imbibition rates and surface area are no longer limiting. Hypertrophied gut and gut villi function efficiently regardless of nutrient concentration and supply because of their increased surface area. Trophotaeniae are adapted for efficient uptake at low concentration and variable supply because they are external, have a large surface area, and are not limited by imbibition. (Supported by NSF)