Diets and Factors Affecting Feeding Success of Age-0 Gizzard Shad

Diets, food selection, and factors affecting feeding success of small (5-9 mm total length, TL), medium (10-19 mm TL), and large (20-29 mm TL) larval and early juvenile gizzard shad (Dorosoma cepedianum) were examined in 2 large Missouri reservoirs. Diets and food selection shifted from mainly copepod nauplii and cyclopoids to rotifers and phytoplankton as fish grew. Mean length of ingested zooplankton rose slightly as gizzard shad grew from the small to medium length groups and then decreased for the large length group. Feeding success (feeding incidence and mean gut fullness) increased with fish size. Feeding incidences of small and medium gizzard shad were significantly higher at an upstream site than at a downstream site in 1 reservoir, but not in the other. Feeding incidence and, to a lesser degree, mean gut fullness of small and medium gizzard shad usually increased with food abundance, although correlations were weak. Feeding incidence and mean gut fullness were not usually correlated with secchi depth or temperature for any length group. These results indicate large shad are more efficient foragers than small shad and relations among feeding success, fish location, and food abundance may be complex and difficult to document in field studies.

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