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<br />258
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<br />MANAGEMENT BRIEFS
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<br />ing the size of the fish at the beginning of the trial
<br />from that at the end of the trial.
<br />The degree of tissue encapsulation of the DTRs
<br />was judged by the thickness of the tissue covering
<br />all or part of the transmitter. Encapsulation was
<br />judged slight when there was a thin, easily ruptured
<br />layer of tissue (adhesions) covering part or all of
<br />the OTR, which was still visible through the cap-
<br />sule. A moderate degree of encapsulation was re-
<br />corded when the DTR was covered with thickened
<br />tissue but remained visible. Heavily encapsulated
<br />DTRs were not visible through thickened tissue
<br />adhesions. Massive adhesions of fibrous connec-
<br />tive tissue, whether the DTR was free or encap-
<br />sulated, was judged to be abnormal.
<br />For the second experiment, 50 rainbow trout
<br />were obtained on 21 October 1986 from brood
<br />stock at the Jones Hole National Fish Hatchery,
<br />Jones Hole, Utah. They were used to evaluate ex-
<br />pulsion of DTRs with different coatings. The fish
<br />were placed inside elevated concrete raceways
<br />(dcpth, 0.9 m; surface area, 4.5 m2) on 28 October
<br />1986, ancsthetized as above. weighed, measurcd
<br />(standard length, SL), and implanted by thc junior
<br />author. Twenty DTRs were coated with beeswax,
<br />20 with paraffin (Parowax@l), and 10 with siliconc
<br />(Silastic@ 382 medical grade elastomer). Beeswax
<br />and paraffin DTRs were solid cylinders cast to
<br />shape in smooth, washed aluminum foil and al-
<br />lowed to harden. The silicone-coated DTRs were
<br />round wooden dowels of the same size. Each DTR
<br />was of medium size and weighted to 10 g by in-
<br />sertion of a lead pellet, which was covered with
<br />one of the coatings. After surgery, the implanted
<br />fish were returned to the concrete raceway and held
<br />at II oC in circulating well water. The fish were fed
<br />a diet of pelleted food at 2% body weight/d. Race-
<br />ways were inspected daily to assess fish health and
<br />to look for any expelled DTRs. The experiment
<br />was terminated after 127 d (4 March 1987) when
<br />the water supply was inadvertently turned offand
<br />all fish died. The fish were frozen on that date and
<br />necropsied I week later.
<br />In the first experiment, one large DTR with its
<br />paraffin coating intact was found on the bottom
<br />of the tank 77 d after surgery. No other DTR was
<br />expelled during the 4l9-d study (4% expulsion rate),
<br />although one fish presumably escaped the tank and
<br />was missing at termination of the study. The ratio
<br />of transmitter weight to fish weight was similar for
<br />beeswax and paraffin groups: small DTRs, 0.5
<br />(beeswax) and 0.6% (paraffin); medium DTRs, 0.7
<br />and 0.7%; large DTRs. 1.4 and 1.3%.
<br />Both test groups of fish increased in average
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<br />weight and length during the study (final means
<br />were 383 mm and 70 I g for the beeswax group
<br />and 376 mm and 629 g for the paraffin group; N
<br />= 12 for both groups). The average increase in
<br />weight (mean, 211.9 g; SD, 254.3) or length (mean,
<br />44.7 mm TL; SD, 32.3) of fish receiving beeswax
<br />implants did not differ significantly from increase
<br />in weight (116.2 g; SO, 164.2) or length (29 mm;
<br />SD, 25.8) of fish with the paraffin implants (Stu-
<br />dent's (-test, P > 0.3). The one fish that expelled
<br />its DTR grew 19 mm (4.5%) during the study but
<br />lost 60 g (6.7%). There were no apparent relation-
<br />ships between the degree of DTR tissue encap-
<br />sulation, internal conditions in the fish, and the
<br />type of DTR coating. However, four of five fish
<br />that developed thick layers of connective tissue
<br />around the DTRs had beeswax-coated DTRs.
<br />Three fish (two with paraffin and one with bees-
<br />wax) had internal bleeding and visible tumors.
<br />In the second experiment, of the 50 fish im-
<br />planted 8 (16%) expelled their DTRs, which were
<br />recovered from the tank. One beeswax-, three par-
<br />affin-, and four silicone-coated implants were ex-
<br />pelled. The first expulsion was a paraffin DTR at
<br />52 d; the first silicone DTR was found at 67 d;
<br />and the single beeswax expulsion occurred at 116
<br />d. At study conclusion, fish remaining in all three
<br />study groups had increased in size (probabilities
<br />are (-tests of the size change)\ beeswax group by
<br />an average 38 mm (P = 0.0 I, N = 19), paraffin
<br />group by 40 mm (P = 0.0 I, N = 17), and silicone
<br />group by 32 mm (P = 0.13, N = 6). Average final
<br />size of the 8 fish that expelled DTRs (339 mm SL)
<br />did not differ significantly from that of the 42 fish
<br />that retained them (359 mm; (-test, P = 0.14). The
<br />ratio of DTR to fish weight was about 1.5% for
<br />beeswax dummies and paraffin and 1.4% for sil-
<br />icone dummies.
<br />When the fish were necropsied, all 19 DTRs
<br />with beeswax were encapsulated (9 moderate to
<br />heavy, 10 slight). Six with paraffin were not en-
<br />capsulated and 11 were encapsulated (1 medium,
<br />10 slight). Of the six with silicone, four were mod-
<br />erately, one was slightly, and one was not encap-
<br />sulated. Six fish presumably voided their DTR
<br />through their anus because their intestines were
<br />enlarged and their body walls were intact. Two of
<br />the fish presumably lost their DTR through the
<br />body wall, because their incisions were partly open
<br />and the old wounds ended in a blind sac.
<br />Expulsion of coated DTRs was low in the rain-
<br />bow trout we studied (3% beeswax, 13% paraffin,
<br />40% silicone). The average expulsion rate of par-
<br />affin-coated DTRs (13%) that we recorded was
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