The Effects of Feeding Restriction on Metallothionein Levels and Ethoxyresorufin-O-Deethylase Activities in Mummichogs

Abstract

Pollution exposure is thought to affect animals through increased maintenance costs, which lead to a decrease in the energy available for other production processes. This can cause weight loss in animals that are chronically exposed to sublethal pollution levels. Starvation and food deprivation have been shown to affect the expression of commonly used bioindicators in fish. The experiments reported in this article were designed to examine the effect of dietary restrictions (in the absence of pollution exposure) on metallothionein and ethoxyresorufin-O-deethylase (EROD; an indicator of CYP1A1 expression) levels in mummichogs Fundulus heteroclitus, a fish that has been extensively examined as an environmental bio-indicator species. Dietary restriction over a 35-d period led to weight loss and alterations in physiological indicators (condition index, liver glycogen, and RNA–DNA ratio) consistent with a reduction in available food. Liver EROD activity increased up to 20-fold on a gram basis and 7-fold on a total-liver basis after 35 d of food restriction. The induction of EROD activity was dependent on the level of caloric restriction. Metallothionein levels initially decreased but then increased slightly to near baseline levels after 35 d of dietary restriction. These results are discussed in the context of using mummichogs as bioindicators of pollution exposure.