Selection and Digestive Efficiencies of Gizzard Shad Feeding on Natural Detritus and Two Laboratory Diets

Abstract

Selective feeding on and digestion of detritus in surface sediments (organic matter < 10%, nitrogen < 0.4%) by age-0 and adult (ages 3 and 4) gizzard shad Dorosoma cepedianum in Acton Lake, Ohio (water temperature = 15–18°C) were compared with those of age-0 fish fed two particulate diets (low-quality diet: organic matter = 10%, nitrogen = 0.3%; high-quality diet: organic matter = 89%, nitrogen = 6.7%) at 18°C in the laboratory. Fish feeding on natural detritus and the low-quality diet exhibited mean selection efficiencies, ratios of nutrient weight percentages in the gizzard to those in the sediment or food, of 1.8–2.9 for total organic matter, 2.4–4.4 for total carbon, and 3.2–13.2 for total nitrogen. Fish fed the high-quality diet exhibited no selective feeding. Mean digestive efficiencies, 100 [ 1 – (feces value ÷ gizzard value)], for total organic matter, total carbon, and total nitrogen in the diets had ranges of 50–66, 51–64, and 62–84%, respectively. Age-0 fish feeding on natural detritus and the two laboratory diets exhibited similar digestive efficiencies. In addition, age-0 and adult gizzard shad were equally efficient at digesting the components of natural detritus. Gizzard shad apparently can ingest selectively the more nutritious portions of low-quality particulate diets in the field and laboratory and digest a substantial proportion of the nutrients present.