A study was conducted to determine apparent digestibility coefficients for dry matter (ADMD), crude protein (ACPD) and gross energy (AED) of selected ingredients in diets for juvenile Penaeus setiferus. Ingredients tested were corn grain, cottonseed meal, crab meal, grain sorghum, meat and bone meal, menhaden fish meal, rice bran, rice grain, shrimp meal, soybean meal, squid liver powder, wheat flour, wheat gluten, wheat middlings and wheat shorts. ADMD coefficients of test ingredients ranged from 22% to 100% and appeared to be related to the fibre, ash and starch content of the ingredient. ACPD coefficients ranged from 58% to 100%. Plant protein supplements (soybean meal and cottonseed meal) were utilized as efficiently as, or better than, animal protein supplements (squid liver powder, menhaden fish meal, meat and bone meal, shrimp meal and crab meal). ACPD coefficients for meat and bone meal, shrimp meal and crab meal (58-59%) were significantly lower than those for menhaden fish meal (76%) and squid liver powder (82%). AED coefficients (44-100%) varied significantly among plant products of similar proximate composition. Corn grain and wheat flour were better utilized by P. setiferus than other high-starch energy supplements. Wheat gluten exhibited the highest ADMD, ACPD and AED coefficients of all ingredients tested.

Abstract— In vitro enzyme assays are rapid, inexpensive techniques for estimating protein digestibility of feed ingredients. Three assays—the Lazo single‐enzyme assay with porcine trypsin; the Hsu multi‐enzyme assay with porcine trypsin, α‐chymotrypsin, and peptidase; and the Satterlee multi‐enzyme assay with porcine trypsin, α‐chymotrypsin, peptidase, and bacterial protease—were used to estimate relative protein digestibility (RPD) of selected feed ingredients used in diets for the Pacific white shrimp Penaeus vannamei. Ingredients tested were casein, gelatin, rice bran, shrimp meal, soybean meal, wheat gluten, and six varieties of fish meal. A highly significant, inverse, linear relationship existed between final pH in each of the enzyme assays and in vivo apparent protein digestibility of the ingredient in P. vannamei feeding trials. Ranking of RPD coefficients obtained in the Lazo single‐enzyme assay followed closely the ranking of published in vivo apparent protein digestibility coefficients for the same ingredients in P. vannamei digestibility trials. Results indicated that a single‐enzyme assay with porcine trypsin identified differences in protein digestibility of feedstuffs in vitro as well as the two multi‐enzyme assays tested. The porcine‐trypsin, single‐enzyme assay appears to be a potentially useful tool for evaluating protein quality and relative protein digestibility of feedstuffs for P. vannamei.

Consumption of O2by planktonic communities of pond waters may be predicted from chemical oxygen demand (COD) and temperature (r 2 -0.85). In ponds where planktonic organisms are the major source of turbidity, Secchi disk visibility may also be used to estimate COD (r 2 -0.81) or consumption of O2 by planktonic communities (r 2 = 0.82). A computer simulation model for nighttime decline in dissolved oxygen (DO) concentrations was developed for channel catfish ponds. This model incorporated data on plankton respiration from the present study, data from the literature on respiration by fish, respiration by organisms in the mud, and O2 diffusion. The validity of the model was tested for two catfish ponds. Measured and calculated DO concentrations usually agreed within -+10%. Secchi disk visibility determination should be used in the computer simulation to estimate O2 consumption by plankton whenever possible. However, COD values may be used when ponds contain appreciable clay turbidity. Series of tables were prepared which give the minimum acceptable Secchi disk visibility and the maximum permissible COD which may be tolerated in a particular pond without danger of DO depletion during the night. These tables will be useful to fish pond managers. A simple, graphical technique for estimating DO concentrations at dawn from DO measurements made at dusk and 2 to 3 h later also gave good estimates of nighttime DO decline. Although this technique has several limitations. it will be useful when it is not possible to measure COD and when Secchi disk measurements cannot be used to estimate O2 consumption by plankton. Can. 32:1283-1288. BOYD. C. E. 1973. The chemical oxygen demand of' waters and biological materials from ponds. Trans. Am. Fish. Soc. 102:606•511. ß 1976. Evaluation of a water analysis kit. Auburn Univ. Agric. Exp. Sta., Auburn, Ala. Leaflet 92.3 pp. ß 1977. Evaluation of a water analysis kit. J. Environ. Qual. 6:381-384. --, E. E. PRATHER, AND R. W. PAaI½S. 1975. Sudden mortality of a massive phytoplankton bloom. Weed Sci. 23:61•57.

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The daytime increase in dissolved oxygen (DO) concentration of pond waters may be estimated from solar radiation, chlorophyll a concentration, and percentage O2 saturation at dawn (coefficient of multiple determination, R2 = 0.83), or from solar radiation, Secchi disk visibility, and percentage O2 saturation at dawn (R2 = 0.80). A computer simulation model for predicting the effects of cloudy weather (low solar radiation) on DO depletion was developed for channel catfish ponds. The model incorporates the equation for estimating daytime DO increase from solar radiation and Secchi disk visibility with components for estimating the nighttime decline in DO from respiration by the plankton, fish, and benthic communities, and the gains or losses from diffusion. Results from the study demonstrated that the combination of dense plankton blooms and low levels of light intensity were closely related to low concentrations of DO.