THE EFFECT OF PHYSICAL CONDITION AND SHOALMATE FAMILIARITY ON PROLIFERATION OF ALARM SUBSTANCE CELLS IN THE EPIDERMIS OF FATHEAD MINNOWS

Ostariophysan fishes have specialized epidermal alarm substance cells( ASCs). In this study, a metabolic cost to the production and maintenan ce of these cells was demonstrated. Fathead minnows Pimephales promela s were maintained on high or low food rations and, to test for the eff ect of social context on the number of ASCs, they were held with eithe r zero or two shoalmates. Shoalmates were familiar (from the focal fis h's shoal), or unfamiliar (fi-om a shoal separated by 1 km from the fo cal fish's shoal). After 16 days, epidermal thickness, number of mucus cells and number of ASCs were all significantly greater for minnows o n the high ration than for those on the low ration. Within the high ra tion group, physical condition was positively correlated with epiderma l thickness and ASC number. The shoalmate treatment had no measurable effect on the epidermis. It was concluded that food availability deter mines investment into ASCs, inferring a trade-off between the cost of ASCs and the fitness benefits they accrue. (C) 1997 Thr Fisheries Soci ety of the British Isles.