| Summary: | Due to the character of the original source materials and the nature of batch digitization, quality control issues may be present in this document. Please report any quality issues you encounter to digital@library.tamu.edu, referencing the URI of the item. Includes bibliographical references (leaves 81-92). Issued also on microfiche from Lange Micrographics. Experiments with juvenile red drum, Sciaenops ocellatus, estimated 1) digestibility, 2) feed consumption and growth, and 3) gastric evacuation rate (GER) for two diets: shrimp tail-meat ("Shrimp"), representing natural forage and a commercially formulated, pelleted feed ("Rangen") of the type used in aquaculture. Effects of fish size on feed consumption, growth and GER also were evaluated for Rangen-fed fish. The digestibility study used 75, 250-g fish to estimate apparent digestibility coefficients (ADCs) for energy, protein and organic matter from chromium-marked, (re)pelleted versions of the Shrimp and Rangen diets. Shrimp provided substantially higher protein, energy and organic matter ADCs. A 32-day feeding trial under laboratory conditions evaluated feed consumption and growth rates. Sixty fish, placed individually in aquaria, were divided evenly into four fish size by diet groups-Large-Rangen, Medium-Rangen, Small-Rangen, Small-Shrimp. Nominal initial weights of Large, Medium, and Small fish were 250, 100, and 25 g. Feed consumption and maximum meal size, both measured as dry feed weight per unit live fish weight, for Rangen-fed fish decreased with increasing fish size. For Small fish, maximum meal size was about the same for Shrimp and Rangen, although examination of the stomach contents of Shrimp-fed fish just after feeding revealed the unexplained disappearance of 51% of the Shrimp diet, making interpretation of the Shrimp-consumption data problematic. A power-function model of fish growth fit to the growth data for Rangen-fed fish had a weight exponent of 0.52. A 33% higher growth rate was observed for Small fish fed Shrimp, compared to those fed Rangen. The serial-slaughter method and exponential-decay model were used to evaluate differences in GER between Rangen- and Shrimp-fed fish. Diet, but not fish weight, significantly affected the GER rate constant (Shrimp, 0.213 h??; Rangen, 0.100 h??), although comparison with two prior studies suggests that GER for the Rangen and Shrimp diets may be more similar when GER is evaluated over longer intervals than the 8 h used in this study. Results from the three experiments taken together suggest that energy-dense commercial diets are eaten less avidly and processed less efficiently by red drum, as compared to more natural forages.
|
|---|