Donald L. Garling

Pretreatment of Soybean Meal with Phytase for Salmonid Diets to Reduce Phosphorus Concentrations in Hatchery Effluents

Abstract Performances of rainbow trout (Oncorhynchus mykiss) fed experimental diets containing phytase-treated or untreated soybean meal with graded levels of supplemental phosphorus (P) were compared with the performance of rainbow trout fed a standard commercial feed. Growth rates and feed conversions (feed fed/weight gain) of fish fed diets containing phytase-treated soybean meal were equal to or significantly better (P 0.05). Pretreatment with the enzyme phytase increased P availability in soybean meal by hydrolyzing phytin P to an available inorganic form. Converted phytin P replaced supplemental P in the diet and was utilized effectively by rainbow trout. The lower dietary P levels resulted in a 65–88% reduction of P in the effluent. Juvenile fish (1.9 g/ fish, mean initial weight) fed a commercial feed releas...

Pathways of Food Uptake in Native (Unionidae) and Introduced (Corbiculidae and Dreissenidae) Freshwater Bivalves

Abstract Nineteen species of adult freshwater bivalves were able to use water currents generated from within the mantle cavity to move non-suspended algae into the shell through non-siphon areas such as the anterior shell valve edge and the mid-ventral point of the shell. This was in addition to, and not in replacement of, uptake of planktonic algae through the inhalant siphon. Algae obtained from both the non-inhalant siphon areas and the inhalant siphon were equally captured and transferred to the stomach. Pseudofecal release was also more complex than typically stated. Pseudofeces were released from the inhalant siphon (as expected), plus from the anterior shell margin, and at the mid-point along the ventral shell edge (non-dreissenids). Pseudofeces that settled near the ventral shell margin was accessible for future uptake back into the mantle cavity. There were no species or body size differences in ability to capture food from non-planktonic sources. The extent to which natural populations utilize benthic food resources remains to be determined. However, our study demonstrates that bivalve communities are very adaptable in accessing a variety of food resources from both suspended material in the water column, as well as organic material from the sediments.

Dietary Androgen-Estrogen Combinations in Growth Promotion in Fingerling Rainbow Trout

Abstract Eight semipurified diets containing various combinations (totaling 2.0 mg/kg diet) of the androgens 17α-methyltestosterone (MT) and 5α-dihydrotestosterone (DHT) and the estrogen estradiol-17β (ES) were fed to four replicate groups of rainbow trout (Salmo gairdneri) fingerlings (initial weight = 0.7 g) for 10 weeks to determine relative growth-promoting effectiveness. Fish fed MT alone or in combination with DHT gained 27.3% more body weight than controls (P 0.20) on body weight. Feed conversion (weight of feed fed/fish weight gained) and average weight gain were recorded over bimonthly periods to examine the effects of treatments on these characteristics. Methyltestosterone enhanced growth (P < 0.05) without changing feed utilization. Decreases (P < 0....

Effect of Feed Color on Feed Acceptance and Growth of Walleye Fingerlings

Abstract Groups of walleye (Stizostedion vitreum vitreum) fingerlings (4.0 ± 0.3 cm total length), reared in water-upwelling units, were converted from a live diet to a red, yellow, or green, semipurified, soft diet over a 10-d period. Results of this experiment suggest that a high percentage (up to 90%) of small walleye fingerlings can be converted from live food to a semipurified diet whose color contrasts with the color of the rearing container.