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experimental group was held in one Heath Tecna incubator stack. Plastic Bio-rings, Bio-saddles and Vexar netting added to separate trays provided a rugose incubation substrate. Flow in the Heath trays was 5 gpm, with an initial egg density of 15,400 per tray. The tanks housing all groups were covered with black plastic sheeting to exclude light. When absorption of the yolk was nearly complete, the plastic covers were removed which allowed light to stimulate swim up activity. The Heath tray group was then removed from the plastic substrates and placed on floating trays in a separate tank. Six groups of 100 fish were randomly taken from each tank and weighed using a triple beam balance. The data were used to determine an average weight per fish for each of the three experimental groups. This weighing procedure was used periodically throughout the rearing period. We began feeding the fry daily when swim up was observed. When it be- came obvious that fry in the deep baskets were not swimming up, they were transferred to the shallow floating trays to encourage them to do so. Once feeding began fish were fed eight times daily. Fish were gradually released from trays to tanks as they learned to feed. The diet first consisted of BioDiet #1 Starter, which was changed to a mixture of Silver Cup #0 salmon starter and BioDiet #1, and finally the latter was gradually phased to Silver Cup #1 trout crumbles. All groups were fed 6% body weight daily, the amount being reduced to 5% after two weeks. RESULTS Within two days after hatching, alevins incubated on the smooth-screened substrates began to show signs of yolk sac malformation and coagulation. As development progressed this condition worsened, with a distinct nipple form- ing on the ends of the yolk sacs of the afflicted alevins. In contrast, alevins incubated in the rugose plastic substrates did not exhibit yolk sac malformation. Their yolk sacs appeared normal, without coagulated nipples, throughout the incubation period. Also, fry in the rugose-substrate group absorbed their yolk sacs sooner than fry in either of the smooth screened substrate groups. However, feed was introduced simultaneously to all groups. After seven weeks of feeding, fry that had been incubated in the plastic substrates averaged 20.5% heavier than fry from the smooth-screen groups (Table 1). During the same seven weeks, the two smooth-screen groups had an average cumulative mortality of 6.7% compared to 3.9% for the plastic-substrate group (Table 2). TABLE 1. Average weight of brown trout fry incubated with rugose plastic substrate and two treatments of smooth screened substrate after seven weeks of feeding. Plastic substrates Smooth screen, trays Smooth screen, baskets x wt. (g) .546 .450 .456 88