Four replicates of 50 rainbow trout (Salmo gairdneri) fingerlings each were assigned to each of seven dietary protein levels from 30 to 60% in 5% increments. Percentage weight gains for 10 wk were related to dietary protein levels using an analysis of variance and multiple comparisons of the means, a "broken line" analysis, and a polynomial regression analysis. When correctly used, one of these techniques should lead to a reasonable conclusion concerning dietary protein requirements. However, the polynomial regression analysis has the advantage of being continuous, like the relation of growth to dose, and should be more accurate than the other methods when the intervals between experimental dietary nutrient concentrations are wide. The polynomial regression analysis also provides the basis for making economic decisions relative to protein requirements for maximum economic returns.

Rainbow trout (Salmo gairdneri) juveniles maintained at 10 and 20 ppt salinity were fed seven diet treatments from 30 to 60% protein in 5% increments for 10 weeks. The fish were stocked in cones, initially 50 fish per cone. Biweekly weights of diets and fish were determined and mortality was recorded daily. Percentage weight gain, gross diet efficiency, and protein efficiency ratio (P.E.R.) were computed. The minimum protein levels required for fish to achieve highest performance using these criteria were 40 and 45% for those maintained at 10 and 20 ppt, respectively. Mortality was significantly (P < 0.05) higher for fish maintained at the higher salinity. Analyses of the fish carcasses were conducted at the beginning and end of the experiment on representative samples to estimate the grams protein retained and apparent net protein utilization (N.P.U.) to verify the above findings. All the available data showed that dietary protein was of major consequence on all measurements until the minimum required level of protein in the diet was reached, while salinity was of minor consequence. P.E.R. and apparent N.P.U. were 2.10 and 34.4, respectively, for casein diets at the 40% protein level.

No abstract

AND D. B. ROARABAUGH. 1981. Effectiveness of fine mesh cylindrical wedge-wire screens in reducing entrainment of Lake Michigan ichthyoplankton. Can. J. Fish. Aquat. Sci. 38: 120-125.Samples of ichthyoplankton entrained through 2 . 0 -m and 9.5-mm-slot opening cylindrical wedge-wire screens and through an open pipe (control) were collected in June, July, and August 1979, 1067 rn off the southeast shore of Lake Michigan at a depth of 10.7 m. Screens were designed for a Wow rate of 1.9 rn3 min-1 at 15.2 cm s-1 through slot velocity. Ambient camposition and density of ichthyoplankton wete determined by net tows. Rainbow smelt (Osmerus mordax), alewife ( A h a pseudoharengus), and yellow perch (Perca flavescensB larvae were common in both entrainment and tow collections. Eggs were found almost exclusively in entrainment collections. Ambient larval fish densities were about 11 times greater than those found in entrainment collections. Total entrainments through either screen and the open pipe were not statistically significant. Larval avoidance and, to a lesser extent, screen exclusion were responsible for the low entrainment. We estimated that about !XI?$ of native fish larvae at the site avoided pumping. . ROARABAUGH. 1881. Effectiveness of fine mesh cylindrical wedge-wire screens in reducing entrainment of Lake Michigan ichthyoplankton. Can. J. Fish. Aquat. Sci. 38: 120-125. Des echantillons d'ichtyoplancton entrain& h travers des krans cylindriques de fil mdtallique cunkiforme ii ouvertures en fentes de 2,Q I B I~ et 9'5 mrn et ii travers un conduit libse (temoin) ont 6t6 recueillis en juin, juillet et aoGt 1973, h 1067 m au large de la rive sud-est du lac Michigan, A une profondeur de 10'7 m. Les krans ont It6 conGus pour une vitesse d'koulement de 1,9 m3 min-I B une vitesse h travers les fentes de 15'2 crn s-I. Des prises au filet 2i plancton ont servi B ddterminer la composition et la densit6 ambiantes de l'ichtyoplancton. Les larves d'Cperlan arc-en-ciel (Osrnerns moniax), de gaspareau (Alsshi psesidoharengus) et de perckaude (Psrcn flrtvescens) sont communes dans l a collections h la fois par entrainement et par filet. On a trouvC des oeufs presque exclusivement dans Bes collections par entrainement. La densit6 des larves de poissons dans i'envirsnnernent est d'environ 11 fois supkrieure h celle trouvke dans ies collections par entrainement. Ii n'y a pas de difldrence significative d'entrainement total soit travers les ecrans, soit dans le conduit libre. L'dviternent par les larves et, 2i un degrd moatadre, l'exclusion par les Ccrans sont responsables du faible entrainement. Nous estimons qu'environ 90% des larves de poissons indigknes au site kvitent d'stre aspirCes par les pompes.

Six purified diets ranging from 30 to 55% protein in 5% increments were fed for 10 wk to duplicate groups of coho salmon (Oncorhynchus kisutch) smolts maintained at 10 or 20‰ salinity. The data indicated that minimum protein requirements did not differ for fish at either salinity, and weight gain and protein retention levelled off after 40% protein in the diet was reached. Salinity had a minor effect on the criteria measured whereas the different dietary protein concentrations were of major consequence. The protein efficiency ratio (PER) of the casein diet containing 40% protein was 2.20 ± 0.11 whereas apparent net protein utilization (NPU) at the same level was 36.1 ± 1.8.