50 Indian J. Fish., 64(3): 50-54, 2017 DOI: 10.21077/ijf.2017.64.3.59243-08 Introduction Gastric evacuation (GE) experiments have been used to quantify the daily ration of fsh fed either natural prey (Elliott and Persson, 1978; Bromley, 1994; Seyhan, 1994; Seyhan and Grove, 1998; Andersen, 2001) or formulated diet (Windell et al., 1972; Talbot and Higgins, 1983; Riche et al., 2004; Bascınar et al., 2016; Khan et al., 2016). GE experiments are often performed by maintaining individual fsh which is considered to be a standard practice (Jobling, 1981; Persson, 1981; Bromley, 1987; Andersen, 1999; Temming and Herrmann, 2001); however, some of the fsh species such as Atlantic herring Clupea harengus, Atlantic mackerel Scomber scombrus, Sprat Sprattus sprattus and sardines Sardinops sagax (Jenyns), cannot be maintained individually. Therefore, GE experiments in such species may only be performed using groups of fshes (Bernreuther et al., 2009). GE experiments in brook trout Salvelinus fontinalis (Mitchill, 1814) based on fsh fed individually have been conducted to determine the efects of body and meal sizes on GE rate (Khan et al., 2016). GE experiments in S. fontinalis fed in group might be interesting to compare the results with that of individually maintained experiments. In this study, small and large size groups of S. fontinalis were fed with three diferent ranges of meal sizes composed of commercial pellets similar to Khan et al. (2016). The main objectives of this study were to determine the efects of meal and body sizes on GE rate of S. fontinalis under group feeding. Materials and methods Fish and experimental conditions Small and large sized fsh of S. fontinalis were procured from the Surmene Faculty of Marine Sciences, Trabzon (Table 1). They were stocked in six separate holding tanks (three tanks for each size fsh) which were facilitated by a recirculating water system where the oxygen saturation was ensured by means of continuous air bubbling. The fsh were fed twice daily with high grade commercial pellets provided by Skretting Aquaculture (protein 44%; fat 21%; fbre 4%; ash 9%) for one month before conducting the experiments. The same batch of commercial pellets was used in all GE experiments. GE experiments All GE experiments were performed at the same time under similar environmental conditions. The experimental fsh were deprived of food for 72 h to ensure complete emptying of the stomachs before providing the experimental diet. Groups of large and small size fsh (exp. 1 and 4 in Table 1) were fed from a known amount of food to the apparent satiation. The uneaten pellets were Efects of meal and body sizes on gastric evacuation rate in brook trout Salvelinus fontinalis (Mitchill, 1814) fed commercial pellets in group feeding N. S. BASCINAR, N. BASCINAR * , U. KHAN * AND K. SEYHAN * Central Fisheries Research Institute, Vali Adil Yazar Cad., No. 14 Sana - 612 50, Yomra, Trabzon, Turkey * Department of Fisheries Technology Engineering, Faculty of Marine Science, Karadeniz Technical University Trabzon - 615 30, Turkey e-mail: seldabascinar@gmail.com ABSTRACT The efects of meal and body sizes on gastric evacuation (GE) of brook trout Salvelinus fontinalis (Mitchill, 1814) were determined following group feeding instead of feeding individually maintained fsh. The GE experiments included small (ranging from 64.75 to 69.72 g) and large fsh (ranging from 161.59 to 170.95 g). Fish in each size group was fed with three diferent meal sizes under similar conditions. The stomach contents were then recovered at predetermined postprandial times by serial slaughtering. The square root model adequately described the course of GE in S. fontinalis independent of meal size. The estimates of mass and length exponent obtained from S. fontinalis fed individually are in line with the present estimates. The result of this study would facilitate the planning and management of feeding regimes for S. fontinalis to minimise food waste and optimise growth. Keywords: Fish size, Group feeding, Meal size, Salmonidae, Square root model