Changes in food habits of largemouth bass Micropterus salmoides were compared with seasonal and annual changes in size composition of a gizzard shad population Dorosoma cepedianum to better understand the temporal dynamics of this species as prey for largemouth bass. Stomachs of 5,283 largemouth bass were examined during spring, summer, and fall from 1978 to 1981. Gizzard shad was the most important species in the diet ofage-I and older largemouth bass in all years. However, the age and size composition, as well as the percentage of the volume contributed by this species to the diet, varied substantially among years and seasonally within each year. Variation of gizzard shad in the diet of yearling and older largemouth bass reflected changes in availability caused by high winter mortality of young-of-the-year gizzard shad in some years as well as by annual variation in the summer growth of this age group. Seasonal gaps in the availability of important size classes of gizzard shad reduced its value as a forage species. Fish contributed a maj or portion of the diet of young-of-the-year largemouth bass in all years but gizzard shad were important only in 1981. Age-0 gizzard shad grew more slowly in 1981, a larger fraction remained vulnerable to predation, and more were eaten by age-0 largemouth bass than in any other year. Storck, T. W., W. Dimond, and S. Miller. 1982. Determination of factors affecting the survival of larval fish and an evaluation of their utilization as food

Daily rings were found in the otoliths of laboratory‐raised, young‐of‐the‐year largemouth bass Micropterus salmoides for at least 151 days after swim‐up. Ring formation began at hatching but the total complement of prolarval rings was visible for only 10–15 days after swim‐up. Subdaily rings were visible in the posterior field but were easily distinguished from daily rings. Both high‐ and low‐contrast tissues were present in otoliths from fish over 45 days old. Sagittal and frontal sections yielded ages of similar accuracy but sagittal sections were much easier and faster to prepare and nearly twice as many were readable. Otolith growth was directly proportional to body growth and the regression intercept was not substantially different from 0.

Age and growth of young-of-year largemouth bass Micropterus salmoides in Lake Shelbyville, Illinois, were determined from daily growth rings in otoliths of fish collected in September of 1980 and 1981. Otolith ages, adjusted for the interval from spawning to the start of feeding (swim-up), revealed that spawning of largemouth bass occurred during 45 days from late April until early June in both years. Spawning occurred at temperatures of 12 to 20 C. In mid-September, 60-75% of the variation in largemouth bass lengths was attributable to age. Older individuals had increased their initial length advantage through faster average daily growth. Back-calculated lengths at 5-day intervals indicated that growth was most rapid to early August and had decreased by mid-September. Growth of individuals that reached swim-up in mid-June declined much more rapidly than growth of individuals that reached swim-up in late May. Differences in growth between largemouth bass that reached swim-up on different dates were associated with differences in their ability to make the transition from an invertebrate to a fish diet. If overwinter survival depends upon length attained during the first growing season, temporal spawning distribution may be an important factor affecting year-class strength.

The survival, angler catch, and harvest of several size-groups of channel catfish Ictalurus punctatus. concurrently stocked into a 6.1-hectare impoundment in central Illinois, increased with size at stocking. However, in the presence of an established predator population and adequate forage, even the largest size-group of channel catfish (mean length, 202 mm total length) suffered 55 and 73% natural mortality, after one and two growing seasons, respectively. Based on the results of this study, the greatest return on investment would be obtained by stocking fish of at least 200 mm total length.

We compared mortality and harvest of 200‐mm and 250‐mm channel catfish Ictalurus punctatus stocked in equal numbers for 4 years in an impoundment containing populations of largemouth bass Micropterus salmoides and bluegill Lepomis macrochirus. Based on a 5‐year creel census, 52–92% of stocked fish were harvested. We found no difference between the stocked length‐groups in terms of mean number caught (N = 365 for 200‐mm and 392 for 250‐mm fish), mean number harvested (66% for 200‐mm and 83% for 250‐mm fish), or mean total weight harvested (116 kg for 200‐mm and 164 kg for 250‐mm fish). Stocking mortality, largemouth bass predation, hooking mortality, and spillway escapement were low for both length‐groups in all years. Harvest was the most important source of mortality in these populations. Growth rates were high, and within years did not differ between length‐groups. High exploitation, fast growth, and low hooking mortality suggest length limits may be useful for deferring harvest of channel catfish in small impoundments until they reach a larger size. Based on analysis of cost effectiveness (catch and harvest/cost of stocking), the return on investment was similar for fish from both length‐groups. Consequently, we do not recommend stocking channel catfish larger than 200 mm for most putgrow‐and‐take fisheries.