While substantial progress has been made in replacing live prey with artificial diets in the feeding of marine fish larvae, it still remains impossible to successfully rear larvae on artificial diets without some period of co-feeding live prey or algae. This study investigated the presence and role of the gastrointestinal hormone cholecystokinin (CCK) in the red drum (Sciaenops ocellatus) to gain a better understanding of the factors limiting the utilization of artificial diets by red drum larvae. Work with other fish species has shown that CCK is the principal hormone which regulates the release of pancreatic enzymes into the gut lumen and emphasizes the potential importance of CCK in early red drum larvae. This work investigated the hypothesis that some signal present in the live prey or algae stimulates CCK and thereby initiates the digestive process in the larvae. First, the nucleotide and amino acid sequence of the putative red drum cholecystokinin precursor was determined and the development of CCK immunoreactive cells was examined. This work showed that red drum CCK is highly similar to CCK in other vertebrates and can be detected in the digestive tract of larval red drum within three days after the initiation of exogenous feeding. Next; postprandial trypsin, CCK, and CCK mRNA responses were quantified in red drum juveniles and larvae over a three hour period. Both CCK and trypsin were increased within thirty minutes following feeding while CCK mRNA levels were increased within the next two to three hours. Finally, the trypsin, CCK, and CCK mRNA responses of red drum larvae to homogenates of live prey and algae were examined. Homogenized rotifers appeared to be sufficient to induce both the CCK and trypsin responses in larval red drum. These results suggest that in addition to other factors, some component of live prey may initiate the release of CCK and prime the digestive process. Understanding these factors and their effects in early larvae may allow us to formulate and produce a prepared diet which will support growth and survival to metamorphosis equal to that provided by live feeds. / text

Ingestion and dispersal of seeds of desirable species by domestic livestock is potentially important as a range improvement practice, but the passage of seed by livestock has only been studied in a fragmented way, particularly for species adapted to rangelands of western North America. The objectives of this research were to examine the effects of different periods of exposure to in vitro and in vivo digestion processes in cattle on the germinability of several grass species, and determine if the in vitro incubation technique is a good predictor of seed fate following passage through the ruminant digestive tract. Seeds of 13 grass species adapted to the Intermountain West were exposed to in vitro incubation for 24, 48, and 72 hours, and then tested for germination at an optimal temperature regime (10°C night/20°C day) in a controlled environment chamber. Germination responses varied considerably among grass species with changes in length of exposure to in vitro incubation, but germination decreased for incubated seed compared to untreated seed for all species. Five species with the highest germination in in vitro incubation trials were fed to Holstein steers in in vivo digestion trials. Approximately 20% of the ingested seeds were recovered for all species 6 days after feeding, and the highest recovery occurred 2 and 3 days after feeding. Germination of undamaged, recovered seeds decreased as passage time through the digestive tract increased. Of the species tested, seeds of Psathyrostachys juncea, Thinopyrum ponticum, Agropyron cristatum X A. desertorum, and Elytrigia repens X Pseudoroegneria spicata have the greatest potential to survive passage through the digestive tract and germinate in appreciable numbers. The in vitro incubation technique may be used as a crude indicator of seed fate following passage through the digestive tract.