MANAGEMENT BRIEFS Evaluation of a Gastric Lavage Method for Use on Largemouth Bass

—The efficiency and delayed mortality caused by a new gastric lavage device was evaluated for use on largemouth bass Micropterus salmoides. A 12-V electric pump was specially fitted to flush stomach contents from largemouth bass larger than 200 mm. The device was easily operated by a single person and removed more than 90% of stomach contents. The lavage technique caused no immediate mortality of largemouth bass. Delayed (7-d) mortality of largemouth bass undergoing gastric lavage was not significantly different from that of controls. Further, mortality did not vary significantly with body length. Overall, the technique appears to be a viable method for rapidly collecting stomach contents from a broad size range of largemouth bass while causing minimal initial and delayed mortality. The food habits of fishes are an integral part of fisheries science, the utility of which are broad in nature. Diet data are valued in the assessment of predator–prey interactions (e.g., Storck 1986), interspecies competition (e.g., Long and Fisher 2000), seasonal diet shifts in prey (e.g., Hartman 1998), the influence of human perturbation (e.g., Pothoven et al. 1999), and in the development of bioenergetic models (e.g., Brandt and Hartman 1993). The inherent variability associated with these data frequently requires collection of large samples to allow accurate quantitative assessment. Methods resulting in high fish mortality, especially of game species, are typically not well received by the public and lack applicability for threatened or endangered species (Haley 1998; Brosse et al. 2002). Further, in low-density fish communities, mortality of even a few individuals may have population-scale implications (Meehan and Miller 1978; Light et al. 1983). Therefore, developing collection methods that adequately meet the quantitative needs of resource managers while having socially acceptable consequences are desired. Techniques employed to collect diet data have been numerous and varied in success (Foster 1977; * Corresponding author: [email protected] Received May 15, 2003; accepted December 19, 2003 Light et al. 1983). Methods developed have included forceps to physically remove prey items (Wales 1962), the use of rigid tube insertion into the stomach to facilitate prey removal (Van Den Avyle and Roussel 1980), emetics (Jernejcic 1969), intestinal flushing (Baker and Fraser 1976), and suction pumping (Giles 1980). Generally, the aforementioned techniques have critical shortcomings, which limit their utility (Foster 1977; Light et al. 1983). Consequently, cumbersome or inefficient techniques have given way to more efficient and rapid procedures, such as gastric lavage. Though apparatus vary, gastric lavage uses pressurized water to flush food items from the stomach of live fishes. In general, removal efficiency is high for the various gastric lavage techniques and postmortality of fish is low. Evaluations of techniques for collecting stomach contents from live fishes have repeatedly demonstrated the efficacy of the technique (Foster 1977; Light et al. 1983; Hartleb and Moring 1995; Brosse et al. 2002). The objectives of this study were to (1) evaluate the efficiency of a portable 12-V electric bilge pump as a means of collecting stomach contents from largemouth bass; (2) determine whether the gastric lavage technique caused significant initial or delayed (7-d) mortality of largemouth bass; and (3) ascertain whether largemouth bass body size influenced the mortality rates of fish undergoing gastric lavage. Though conceptually similar to other gastric lavage techniques developed (Foster 1977; Light et al. 1983; Hartleb and Moring 1995; Brosse et al. 2002), differences in apparatus used in this study, fish species anatomy, and prey item variability certainly warrant further evaluation of new methodologies like those developed here.