Efficiency of Gastric Lavage on Age-0 Brook Trout and the Influence on Growth and Survival

Accurate knowledge of food webs is important in understanding aquatic ecology. One common way to determine the food web structure of an aquatic ecosystem is to perform stomach content analysis. Gastric lavage has developed into the preferred method for collecting dietary data from live fish. The objective of this study was to determine the efficiency of gastric lavage for age-0 brook trout Salvelinus fontinalis. Also, to assess the effects on shortand long-term growth and survival, age-0 brook trout were monitored for 2 months following the gastric lavage procedure. Gastric lavage was extremely efficient (>97% of dry weight; >98% by number) at removing Ephemeroptera, Plecoptera, and Trichoptera larvae fed live to age-0 brook trout larger than 50 mm total length (TL). Neither growth nor survival was significantly influenced by gastric lavage. Long-term survival was excellent (94%) and did not differ from that of control fish. Gastric lavage is thus an efficient, safe method for stomach content analysis of age-0 brook trout larger than 50 mm TL. Accurate food web data are essential in understanding ecology in aquatic systems. Many studies have determined the prey of large adult fish (Diana 1979; Godinho et al. 1997; Eggleton and Schramm 2004; Webster and Hartman 2005), but very few have attempted to assess the diet of very small, age-0 fish in a nonlethal manner. Assessing the diet of age-0 fish is important because age-0 fish with increased energy reserves are more likely to survive difficult periods such as winter (Thompson et al. 1991). Furthermore, age-0 survival can play an important role in determining year-class strength (Hubbs and Trautman 1935; Garvey et al. 2004). It has also been shown that predator capture success rates decrease as prey size increases (Scharf et al. 1998); therefore, increased growth rates of age-0 fish allow them to outgrow predation risk more quickly, ultimately decreasing natural mortality rates. Because of the *Corresponding author: [email protected] 1Present address: Department of Biology, Susquehanna University, 514 University Avenue, Selinsgrove, Pennsylvania 17870, USA. Received September 29, 2010; accepted March 16, 2011 large influence age-0 growth can potentially have on year-class strength, accurate assessments of age-0 diet could help explain much of the variation in year-to-year differences in year-class strength. Gastric lavage has been widely used in fisheries as a tool to determine the stomach contents of live, wild-caught fish. Ensign et al. (1990) used gastric lavage on age-0 brook trout Salvelinus fontinalis and rainbow trout Oncorhynchus mykiss, and noted only two deaths immediately following the procedure. Foster (1977) used gastric lavage as a method for assessing the stomach contents of redfin pickerel Esox americanus (50–300 mm) and largemouth bass Micropterus salmoides (50–450 mm), and reported that the method was nearly 100% effective and had no significant influence on survival. Light et al. (1983) reported that gastric lavage was 98% effective for brook trout ranging from 57 to 355-mm total length (TL). They also monitored 14 fish for 3 weeks after the procedure and reported that no mortality had occurred. Although gastric lavage has been used successfully on small fish in the past, previous researchers did not assess the possible long-term effects or estimate efficiency specifically for age-0 fish. If gastric lavage is going to be used on large numbers of age-0 fish, a better understanding of its efficiency and possible influences on growth and survival is needed. Because information is needed regarding age-0 fish, one objective of this study was to determine the efficiency of gastric lavage for assessing age-0 brook trout stomach contents. We hypothesized that gastric lavage would be efficient at removing dietary items from age-0 brook trout. The second objective was to determine if performing gastric lavage on age-0 brook trout caused increased mortality or decreased growth. We expected that performing gastric lavage would increase the mortality rate in age-0 brook trout and have a negative influence on growth rates. 530 D ow nl oa de d by [ W es t V ir gi ni a U ni ve rs ity ], [ A nd re w H af s] a t 0 6: 29 0 6 Ju ly 2 01 1 MANAGEMENT BRIEF 531 METHODS Two hundred and ninety age-0 (∼50 mm TL) brook trout were donated from Bowden State Fish Hatchery, Bowden, West Virginia. The fish were transported to the West Virginia University Ecophysiology Laboratory and were maintained in a recirculating tank (0.58 × 0.58 × 2.13 m) at 12.5 ± 0.5◦C. All fish were acclimated to the recirculating system for at least 2 weeks before any gastric lavage experiments were done. During acclimation, fish were fed crushed pelletized fish food (40% protein, 10% fat) ad libitum daily. Gastric lavage technique.—When performing gastric lavage on age-0 brook trout, we simulated the methods of Foster (1977) and Light et al. (1983), with some slight modifications. Our lavage was made from a 5-cc syringe attached to a 16gauge, 57-mm (Model 4052; JELCO, Dublin, Ohio) intravenous catheter tube. All fish were anesthetized with tricaine methanesulfonate (MS-222; 100 mg/L) before gastric lavage was performed. Length (mm, TL) and wet weight (g) of all fish were measured before gastric lavage commenced. The syringe was filled with distilled water (∼5 mL), and the catheter was eased down the esophagus of the fish into the stomach cavity. The water in the syringe was then used to flush the stomach contents of the fish onto a preweighed, glass fiber filter with a pore size of 0.7 μm (Model AP40; Millipore, Billerica, Massachusetts) held by a 500-mL capacity filter unit (similar to Model MF75; Thermo Fisher Scientific, Rochester, New York). While the water from the syringe was being flushed through the fish stomach, the hand that was holding the fish would massage the abdomen walls to help the stomach contents ease out of the cavity. This flushing process was done three times on each fish to simulate a pulsed gastric lavage technique. The filter was placed on a preweighed aluminum pan, and stomach contents were counted and oven-dried at 80◦C to a constant weight. Gastric lavage efficiency.—Ninety of the 290 brook trout were selected for the gastric lavage efficiency experiments. The experiments were run on 16, 19, and 21 March 2010. The day before each of these dates, 30 brook trout were selected and separated evenly (five fish per tank) into six (330 × 190 × 203-mm) clear plastic fish tanks. All six of the clear plastic tanks had 3.18-mm holes drilled in the sides and were partially submerged in a larger (0.58 × 0.58 × 2.13-m) tank that was part of the recirculating system in which the fish had previously been. On the mornings of 16, 19, and 21 March 2010, live aquatic insect larvae from the orders Ephemeroptera, Plecoptera, and Trichoptera were collected from Coburn and Aarons creeks, Monongalia County, West Virginia. All aquatic insects used in this portion of the experiment were less than 15 mm in length (not including cerci). The families of aquatic insects used in this experiment are listed in Table 1. Once the insects had been captured, sorted to order, and counted, they were fed to the fish. Fish in two tanks were fed only Ephemeroptera, fish in two other tanks were fed only Plecoptera, and fish in the last two tanks were fed only Trichoptera (with cases removed). Thirty TABLE 1. Families of aquatic insects from the orders Ephemeroptera, Plecoptera, and Trichoptera captured from Aarons and Coburn creeks on 16, 19, 21, and 22 March 2010 and fed to brook trout during laboratory experiments.