GROWTH AND PHYSIOLOGICAL-RESPONSES TO SURGICAL AND GASTRIC RADIO TRANSMITTER IMPLANTATION TECHNIQUES IN SUBYEARLING CHINOOK SALMON (ONCORHYNCHUS-TSHAWYTSCHA)

We examined the effects of surgical and gastric transmitter implantati on techniques on the growth, general physiology and behavior of 230 su byearling chinook salmon (Oncorhynchus tshawytscha, Walbaum) (100 mm-1 54 mm fork length). The transmitter weighed 1.3 g in air (0.9 g in wat er) and comprised, on average, 6% of the body weight of the fish (in a ir). Individuals were randomly assigned to an experimental group (cont rol, surgical or gastric) and a sampling period (day 5 or day 21). Rel ative growth rate % as expressed as % body weight gained/day. General condition was assessed by necropsy. Physiological response variables i ncluded hematocrit, leucocrit and plasma protein concentration. The me an relative growth rates of control, surgical and gastric fish were no t significantly different at day 5. By day 21, the gastric group had a significantly lower relative growth rate (1.3%) as compared to the su rgical group (1.8%) and the control group (1.9%) (P = 0.0001). Mean he matocrit values were significantly lower in the surgical (41.8%) and g astric (42.2%) groups as compared to controls (47.3%) at day 5 (P = 0. 01), but all were within normal range for salmonids. No significant di fferences in hematocrit values were detected at day 21. Leucocrit valu es for all groups were less than or equal to 1% in 99% of the fish. Bo th tagged groups had significantly lower mean plasma protein levels as compared to controls at day 5 (P = 0.001) and day 21 (P = 0.0001). At day 21 the gastric group (64.4 g 100 ml(-1)) had significantly lower mean plasma protein levels than the surgical group (68.8 g 100 ml(-1)) (P = 0.0001). Necropsies showed decreasing condition of gastrically t agged fish over time, and increasing condition of surgical fish. Paire d releases of surgically and gastrically implanted yearling chinook sa lmon in the lower Columbia River in spring, 1996 revealed few signific ant differences in migration behavior through two reservoirs. We concl ude that gastrically implanted fish show decreased growth and conditio n over a 21 d period. We recommend a surgical implantation method for long-term studies of juvenile salmonids, however, gastric implantation may be suitable for short-term studies.