Ž .
Table 1 continued Substances with parasiticidal
Treatment Control, mean
Treated, mean Dead eels
Ž .
effect data on substance concentration
infection category infection category
in treated group Ž
. Ž
. Ž
. ppm
S.D. S.D.
due to toxicity Ž
. Ž
. Ž
. Nitrate 18
3000 2.0 0.8
2.2 0.4 Ž
. Ž
. Ž
. N-methyl-glucamine 19
50 2.5 0.5
1.4 0.5 Ž
. Ž
. Ž
. Oxolinic acid 20
50 2.2 0.4
2.8 0.4 Ž
. Ž
. Ž
. Oxytetracycline 21
80 2.5 0.5
2.1 0.6 Ž
. Ž
. Ž
. pH 5 22
2.1 0.6 2.4 0.5
Ž .
Ž .
Ž .
Potassium oleat, 35 23 4
2.0 0.8 2.0 0.0
60 Ž
. Ž
. Ž
. Quinidine sulphate 24
30 2.6 0.5
2.6 0.5 Ž
. Ž
. Ž
. Sodium chloride 25
4000 1.8 0.5
1.5 0.5 Ž
. Ž
. 10 000
2.8 0.4 2.6 0.5
Ž .
Ž .
Ž .
Sulfadimidinum 26 75
2.5 0.5 2.5 0.5
Ž .
Ž .
Ž .
Tap water 27 2.8 0.4
2.5 0.5
w
Ž .
Ž .
Ž .
Tiguvon 28
20 2.8 0.4
3.0 0.0 20
Ž .
Ž .
Ž .
Toltrazuril 29 5
2.3 0.7 2.6 0.5
20 Ž
. Ž
. Ž
. 4-Hexylresorcinol 30
1 2.3 0.6
1.3 0.6 70
a
In tap water.
Ž Ž
.. including the biofilters
bithionol and formalin , to the recirculation unit while Ž
w
. biofilters were isolated temporarily 1 h, Detarox AP
and formalin or to one or more Ž
w
. rearing tanks temporarily isolated from recirculation 3 h, Virkon PF
. In the recircula- tion unit, the substances were added to the water reservoir supplying the rearing tanks. If
biofilters were included during the experiment, treated fish were examined 3–4 h after the initial exposure. If biofilters were isolated during the experiment the treatment was
regarded finished when rearing tanks were reconnected to biofilters and the fish were examined the following hour. For the bath treatments in separated tanks, untreated eels
in the same system were used as controls. Groups of eels caught before treatment and transferred to the aquarium with system water were used as controls for treatments
involving the entire recirculation system. Number and size of eels in a control group
Ž .
equalled the number of eels from the treated group Table 3 . Reinfection of treated eels Ž
was examined 3 and 7 days after some of the treatments no control groups on days 3 .
Ž and 7 . Changes in feeding activity and mortality were evaluated subjectively based on
. experience 3–4 weeks posttreatments. Effects of treatment on biofilters were examined
Ž
w y1
. by determining the ammonia concentration Merck , resolution: 0.5 mg l
every second day for 1 week posttreatment. High increase of ammonia was assumed to
indicate a negative effect of treatment.
3. Results
3.1. Aquarium trials 3.1.1. Screening substances
Ž .
Thirty substances formalin and tap water trials not included were screened for Ž
. Ž
. Ž
efficacy against T. jadranica on eels Table 1 . Acriflavin 25 ppm, , bithionol 0.25
.
w
Ž .
Ž
y1
. ppm , Detarox AP
30 ppm, tap water fresh raw squeezed garlic 0.2 g l , 200 ppm ,
Ž .
Ž .
w
Ž malachite green 1 ppm , potassium permanganate 20 ppm and Virkon PF
vet. 20 .
w
Ž .
ppm removed all trichodinids from the eel. Detarox AP 20 ppm, tap water; 45 ppm ,
Ž .
Ž .
Chloramine T 50 ppm and formalin 75 ppm, tap water removed almost all the parasites. Chloramine T and potassium permanganate were toxic to eels in therapeutic
concentrations, while none of the other effective substances appeared to be acutely toxic at a therapeutic dose. The remaining substances or concentrations showed no or little
Ž .
effect on the parasites; however, some were toxic to the eels Table 1 . For further Ž
.
w
Ž .
w
Ž examination bithionol 0.25 ppm , Detarox AP
45 ppm and Virkon PF vet. 20
. ppm were selected and these showed a high parasiticidal effect after 1, 1 and 3 h
Ž .
respectively Fig. 1 in aquarium experiments. 3.1.2. Tolerance
Bithionol caused mortality to pigmented eels and to glass eels at drug concentrations Ž
. higher than 0.4 or 0.1 ppm for 5 or 96 h, respectively Table 2 . Mortality was observed
Ž .
Fig. 1. Effect of exposure duration. Mean infection categories of eels ns 5 infected with T. jadranica. Eels Ž .
w
Ž .
w
were exposed to bithionol a , Detarox AP b or Virkon PF
vet. Infection categories were determined 4 h Ž
. Ž
. post bithionol and Vikon and 2 h postexposure Detarox .
Table 2 Tolerances of eels to Bithionol, Detarox AP
w
and Virkon PF
w
vet.: maximal concentration of the substances Ž
. ppm were 100 of the eels survived
Substance 5 h
96 h Bithionol
Glass eels 0.4
0.1 Pigmented eels
0.4 0.1
w
Detarox AP Glass eels
25 25
Pigmented eels 100
70
w
Virkon PF vet.
Glass eels 10
10
a
Pigmented eels 70
30
b
Pigmented eels 40
10
a
At 0, 5 and 10 ppt sodium chloride.
b
At 15 ppt sodium chloride.
after approximately 2–3 h of exposure. Mortality of pigmented eels occurred when exposed to Detarox AP
w
at concentrations higher than 100 or 70 ppm in 5 or 96 h, Ž
. respectively Table 2 . Mortality was observed after approximately 1 h of exposure.
w
Ž .
w
Glass eels tolerated maximally 25 ppm Detarox AP Table 2 . Virkon PF
vet. in concentrations higher than 70 or 30 ppm for 5 or 96 h, respectively, caused mortality to
pigmented eels at a salinity of 0–10 ppt . At a salinity of 15 ppt Virkon PF
w
vet. caused mortality at concentrations higher than 40 or 10 ppm at an exposure time of 5 or 96 h,
Ž .
w
respectively Table 2 . Mortality was observed after 3–4 h of exposure. Virkon PF Ž
. vet. concentrations higher than 10 ppm 0 ppt salinity caused mortality to glass eels at
Ž .
exposure times of both 5 and 96 h Table 3 . Mortality was observed after approximately 2 h of exposure.
3.2. Full-scale trials in eel farms Bithionol at 0.1 ppm reduced the mean infection categories of 1.2 and 2.3 to 0.1
Ž .
Trial B1 and B2, Table 3 . The mean infection category increased to 1.5 within 1 week Ž
. posttreatment B1 . No negative effects on eels or biofilters were observed. Detarox
AP
w
concentrations of 45 or 55 ppm reduced the mean infection categories of 1.5–2.7 Ž
. to 0.0–0.2 D1, D2, D3, Table 3 . Seven days posttreatment the infection categories
Ž .
increased to 1.4 and 0.6 D1 and D3, respectively . After start of exposure the
swimming activity of the eels increased. Between 1 and 11 2 h later their activity appeared to be normal. A few hours after reconnection of the biofilters, feeding activity
was low after which the activity returned to normal. No increase in mortality was observed. Virkon PF
w
vet. was administered as a bath treatment of 3 h in temporarily Ž
.
w
isolated rearing tanks V1 and V2, Table 3 . Initial exposures of 20 ppm of Virkon PF vet. effective under laboratory conditions, did not provide sufficient control under
Ž .
w
practical farm conditions data not shown . In subsequent exposures, Virkon PF vet.
added to an initial concentration of 25 ppm and supplemented with 15 ppm 1 h later reduced the mean infection category from 2.9 to 0.1; 3 days posttreatment the category
Ž .
had increased to 1.4 V1 . When supplemented with extra 20 instead of 15 ppm a mean Ž
. infection category of 2.1 was reduced to 0.05 V2 . During the treatments swimming
H.C.K. Madsen
et al.
r Aquaculture
186 2000
221 –
231 228
Table 3 Experimental treatments of trichodiniasis in recirculation plants: Design and efficacy expressed as reduction of infection category. Treated eels were examined 1 h
Ž .
posttreatment duration of treatment: hours of isolation of tanksrbiofilters ; experiments B1, B2 and F2: eels examined 3 h after treatment initiation Ž
. Experimental design
Mean infection category S.D. Ž
. Treatment ppm
No. of Mean
Treated Treatment
Treatment in Isolation of
Control Treated
Treated 3 Treated 7
Ž . examined
weights group:
in isolated the recircu-
biofilters h days later
days later Ž .
Ž . Ž . eels
g total weight
tank s h
lation system Ž
. Ž
. Ž
. Ž
. Ž
. B1 Bithionol 0.1
10 29
0.1 =
2.3 0.5 0.1 0.3
0.5 0.5 1.5 0.5
Ž .
Ž .
Ž .
B2 Bithionol 0.1 10
24 0.1
= 1.2 0.4
0.1 0.3 Ž
. Ž
. Ž
. Ž
. Ž
. D1 Detarox AP 45
15 2–10
5.2 =
1 2.7 0.5
0.2 0.4 0.8 0.4
1.4 0.5 Ž
. Ž
. Ž
. D2 Detarox AP 45
15 2–10
5.2 =
1 1.5 0.5
0.2 0.4 Ž
. Ž
. Ž
. Ž
. Ž
. D3 Detarox AP 55
15 4–6
1.5 =
1 1.9 0.5
0.0 0.0 0.3 0.5
0.6 0.5
a
Ž Ž
. . Ž
. Ž
. Ž
. V1 Virkon PF 25q 15
120 70–250
17.9 3
2.9 0.4 0.1 0.3
1.4 0.7
a
Ž Ž
. . Ž
. Ž
. V2 Virkon PF 25q 20
20 2.8
0.7 3
2.1 0.5 0.05 0.22
Ž .
Ž .
Ž .
F1 Formalin 75 20
125 3.3
3 3.0 0.5
1.0 0.7 Ž
. Ž
. Ž
. Ž
. F2 Formalin 85
10 2–10
5.2 =
1 2.6 1.0
1.2 0.6 2.8 0.5
Ž .
Ž .
Ž .
F3 Formalin 60 10
2–10 4.5
= 2.1 0.6
2.1 0.6
a
Added 1 h later.
activity increased but appeared to be normal 1–2 h posttreatment. No negative effects on feeding activity and mortality were observed. When the treated tanks were reconnected
to the recirculation system no negative effects were seen on the feeding or on the biofilters. A bath treatment of formalin at 75 ppm for 3 h reduced the mean infection
Ž .
category from 3.0 to 1.0 F1, Table 3 . Formalin also reduced the mean infection category from 2.6 to 1.2 when added to a concentration of 85 ppm in a recirculation
Ž .
system biofilters isolated 1 h . However, the mean infection category increased to 2.8 Ž
. Ž
. three days posttreatment F2 . Formalin 60 ppm added to a complete recirculation unit
Ž .
Ž .
biofilters included had no apparent effect on the parasites, fish nor biofilters F3 . All tested substances caused a slightly elevated mucus secretion on skin and gills.
4. Discussion
