Student Research Projects

Effects of Diet on Gut Morphology of Gizzard Shad

Student John Evans
Ashley Wright '10
Faculty Mentor(s)
Department Biology
Course BIO 489: Research in the Natural Sciences


In fish, planktivorous and omnivorous species can vary dramatically in intestine length. Omnivores typically have intestines that are 2-4 or more times the body length, whereas planktivores and other types of carnivores typically have much shorter intestines. Longer intestine length can help omnivores assimilate lower quality vegetative and detrital foods. Previous studies indicate that gizzard shad show a marked ontogenetic diet shift from obligate zooplanktivory to increased detritus consumption above 35mm standard length, with a corresponding increase in intestine length. In addition, the diet of gizzard shad (Dorosoma cepedianum) can vary substantially among lakes, making this species ideal for examining the relationship between diet and intestinal morphology. We examined the gut morphology of Gizzard Shad from six lakes, four from Florida (Apopka, Dora, Griffin and Newnans) where gizzard shad exhibit higher growth and feed on a mixed diet, one from Ohio (Acton), where gizzard shad are typically detritivorous and exhibit lower growth, and one from New York (Oneida), where previous diet analyses have focused primarily on the planktivory of young-of-year fish. We hypothesized that intestine length would be shorter in systems where gizzard shad fed more extensively on zooplankton, and for size classes that fed extensively on zooplankton. Relative intestine lengths showed significant differences among lakes, with intestines averaging 3.4-3.6 times the body length in Acton Lake and Lake Oneida but only averaging 3.0 times the body length in Lake Apopka. We also observed significant changes in relative intestine lengths with fish size. This is most clearly observed in Lake Oneida, with juvenile intestines shifting from 1.1 times the body length at 45mm Standard Length (SL) to 2.6 times the body length at 70mm SL as the fish shifted away from obligate zooplanktivory. Intestines of adult fish from Lake Oneida (253-306 mm SL) typically ranged from 3.5-4.7 times the body length. In addition, relative gizzard mass varied significantly with fish mass and among systems, with gizzards averaging over 2% of body mass in Lakes Apopka and Dora, whereas gizzards were less than 1.3% of body mass in Newnans Lake, Acton Lake and Lake Oneida. Overall, these results indicate that body length and gizzard mass can vary substantially with ontogeny and among systems, providing for effective digestive functioning suitable to local diet.


Science Undergraduate Research Travel Award


National Conference on Undergraduate Research, Mar 31-April 2, Ithaca, NY