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Stable carbon isotope ratios (δ13C) were used to estimate the relative contributions of natural and prepared feeds to the nutrition of golden shiners Notemigonus crysoleucas in ponds. Concurrent feeding trials were conducted in tanks (110 L) and ponds (0.04 ha) to determine the response of golden shiners to three isotopically distinct prepared diets both in the presence (pond) and absence (tank) of natural food. Seston was the primary indicator of the δ13C of natural foods available in the ponds, but δ13C's of free‐swimming, unfed golden shiners provided an additional index. Fish receiving experimental diets were maintained in floating nets within the same ponds. After 6 wk, fish in tanks fed all three diets had acquired the diet label to some degree, while fish in ponds also tracked their respective feeds except for those fed diet 3. This diet contained a large amount of corn meal, which appeared to be poorly assimilated by golden shiners. The use of natural foods by golden shiners fed all three prepared feeds ranged from 40–83% and was inversely correlated with the relative assimilation of the prepared feeds.

Choline is usually supplemented as ruminally protected choline chloride to prevent its degradation in the rumen, but the effects of unprotected choline on ruminal fermentation are unclear. Some research indicates a possible role of dietary fiber on microbial degradation of choline; therefore we aimed to evaluate the effects of unprotected choline chloride on ruminal fermentation and to investigate whether those effects depend on dietary neutral detergent fiber (NDF) concentration. Our hypothesis was that dietary NDF concentration would influence choline chloride effects on microbial ruminal fermentation. We used 8 fermentors in a duplicated 4 × 4 Latin square with a 2 × 2 factorial arrangement, combining 2 factors: (1) dietary NDF concentration and (2) unprotected choline chloride supplementation. Resulting treatments are (1) 30%NDF/Ctrl [30% NDF control diet without supplemental choline (Cho)]; (2) 30%NDF/Cho [30% NDF diet plus 1.9 g of choline ion per kg of dry matter (DM)]; (3) 40%NDF/Ctrl (40% NDF control diet without supplemental choline); and (4) 40%NDF/Cho (40% NDF diet plus 1.9 g of choline ion per kg of DM). Four 10-d periods were completed, each consisting of 7 d for adaptation and 3 d for collection of samples for estimation of nutrient disappearance and daily average concentrations of volatile fatty acids and NH 3 -N. In addition, kinetics of pH, acetate, and propionate were evaluated at 0, 1, 2, 4, 6, and 8 h after morning feeding. On the last day of each period, bacteria pellets were harvested for 15 N analysis and N metabolism. Fixed effects of dietary NDF concentration, unprotected choline chloride supplementation, and their interaction (NDF × Cho) were tested using the MIXED procedure of SAS version 9.4 (SAS Insti-tute Inc., Cary, NC). Choline tended to increase total volatile fatty acid concentrations and decreased acetate molar proportion regardless of dietary NDF concentration, but it increased propionate molar proportion and decreased acetate to propionate ratio only with the 30% NDF diet. Supplementing choline decreased NDF disappearance regardless of dietary NDF; however, organic matter disappearance tended to be reduced only when choline was added to 40% NDF. Our data indicate that unprotected choline chloride effects on ruminal fermentation depend on dietary NDF concentration, allowing for a greater propionate synthesis without decreasing organic matter disappearance when fed with a 30% NDF diet.

We conducted two feeding trials in which golden shiners Notemigonus crysoleucas were given six practical diets: two basal diets with 5% fish meal and either 4% or 10% supplemental lipid (poultry fat [PF]); two prebiotic diets with 2% dairy-yeast prebiotic, 5% fish meal, and 4% or 10% PF; and two 4% or 10% PF diets that contained no fish meal or prebiotic. To compare diet effects in the presence or absence of natural foods, one trial was conducted in indoor aquaria and one was conducted in outdoor pools. Diet effects were assessed by measuring growth, survival, feed efficiency, and body composition in both trials and Fulton's condition factor K in the outdoor pool trial. A subset of fish from the outdoor trial was grown to a larger size for analysis of alternative complement activity (ACH50). The prebiotic enhanced growth and feed conversion ratio (FCR) slightly in the indoor aquarium trial. Weight gain and FCR did not differ among diet groups in the outdoor trial, reflecting the influence of natural foods. Survival in aquaria was higher in fish fed the 10% PF diets than in fish given the 4% PF diets. The prebiotic slightly reduced survival in outdoor pools, but survival was 96% or higher for all diet groups. The K-value was higher in fish that were given 10% PF diets than in fish fed 4% PF diets. Whole-body proximate composition was similar among treatment groups for the aquarium trial. In the outdoor trial, whole-body lipid was higher in fish fed the diets with 10% PF versus those fed diets with 4% PF, and dry matter followed a similar pattern. The ACH50 was similar between golden shiners that were fed diets with the prebiotic and those given diets without the prebiotic. Fish meal did not enhance any of the performance criteria in golden shiners held in tanks or pools. Although prebiotic addition and lipid concentration significantly affected several aspects of fish performance and body composition, some of the differences were numerically small. Economic analysis should be conducted to determine whether addition of a prebiotic or extra lipid to commercial diets is justified for production and distribution of golden shiners.