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Does oral administration of oxolinic acid or oxytetracycline affect feed intake of rainbow trout?
ilquaculture, 92 ( 199 I ) IO9- 113 Elsevier Science Publishers B.V., Amsterdam
109
Does oral administration of oxolinic acid or oxytetracycline affect feed intake of rainbow trout? Svein Olaf Hustvedt, Trond Storebakken and Ragnar Salte .4KlGfFOUSK (institute ofAquacuiture Research]. N-1432 &NLH,
Norway
(Accepted 30 May 1990)
ABSTRACT Hustvedt, S.O., Storebakken, T. and Salte, R., 1991. Does oral administration of oxolinic acid or oxytetracycline affect feed intake of rainbow trout? Aquaculture, 92: 109- 1 13. Short-term oral drug intake was measured in rainbow trout (Oncorhynchus mykiss) using radioactively labelled diets. In Experiment 1, duplicate groups of trout were fed either a control diet without antibiotic addition, or diets containing either 10 g oxolinic acid (OA) or IO g oxytetracycline (OTC) per kg. In Experiment 2, triplicate groups of trout were fed diets containing either 1 or 10 g OA per kg. The trout, weighing 200-900 g, were kept in freshwater at 10°C. The fish were accustomed to feeding to satiation every 20 min, 20 h/day; the drugs were fed over a 6-h period. The amount of radioactive feed ingested by the fish was measured directly on anaesthetized fish with a portable gamma scintillation counter. The results showed that OA in the diet tended to reduce mean feed intake (mean reduction 17%) compared to controls. This reduction was, however, not significant (P=O.O9). Addition of OTC led to a 61% reduction in feed intake (P
INTRODUCTION
Oxolinic acid (OA) and oxytetracycline (OTC) are frequently used in therapy of bacterial infections in aquaculture. The predominant way of administering these antibiotics to fish is systemic treatment via the diet. Thus, knowledge about the acceptance of the feed supplemented with an antibiotic is important for oral treatment regimens. Reduced compliance in drug therapy due to the presence of distasteful drugs is a well known problem both in human and in veterinary medicine. Reduced palatability of medicated feed has earlier been linked directly to the taste of the drug in tests with sulfa derivatives (Gutsell and Snieszko, 1949; Snieszko and Griffm, 195 5; Snieszko and Wood, 1955 ) as well as in a test with erythromycin thiocyanate (Schreck and Moffltt, 1987 ). The aim of this study was to test whether the presence of 0044-8486/91/$03.50
0 1991 -
Elsevier Science Publishers
B.V.
S.O. HUSTVEDT ET AL.
110
OA or OTC in the diet affected the feed intake of rainbow trout (Oncorhynthus mykiss). MATERIALS AND METHODS
This study consisted of two experiments which were undertaken at AKVAFORSK at Sunndalsora. Six groups of rainbow trout (Oncorhynchus mykiss) were kept in indoor 1-m’ libre-glass tanks which were each supplied with freshwater. The lish were all in good health, i.e. no clinical signs of diseases were seen. The photoperiod was 24 h/day. The water flow rates were approximately 10 l/min. Water sources and water quality is described by Austreng ( 1976). In Experiment 1 (Expt. 1 ), each group consisted of 35 fish weighing 628 + 15 1 g (means? s.d. ), and in Experiment 2 (Expt. 2 ), each group consisted of 55 fish weighing 330 + 85 g. The water temperature was maintained at 10 ? 1 ‘C for at least 3 weeks before and during the experimental period. Handling stress was reduced to a minimum in the experiments, and the environment to which the fish were accustomed was maintained since the farming environment may influence feed intake (Ishiwata, 1968) The fish were fed a commercial, dry pelleted diet until 3 weeks prior to the experiments. Then a moist diet was fed, which also served as the control diet (Table 1) . The moist diet was manufactured by using a meat mincer equipped with a 5-mm die. Fish were fed to satiation by automatic feeders every 20 min, 20 h/day. The trout were starved for 12 h before initiation of each experiment. Radioactive silver iodide ( Ag”‘I) was added to each of the diets at a level of 74 MBq/kg in both experiments. In Expt. 1, duplicate groups of trout were fed either the control diet without antibiotic incorporation, or the diet with either 10 g OA or 10 g OTC per kg. In Expt. 2, triplicate groups of trout were fed diets containing either 1 or 10 g OA per kg. Both OA and OTC were supplied by the Norwegian Medicinal Depot, Oslo, Norway. The medicated diets were fed every 20 min over a 6-h period. Then all fish TABLE 1 Formulation
of the moist control diet
Ingredients
g/kg
Capelin Cooked Capelin Alginate Water
367 180 107 13 333
meal (NorSeaMink) wheat (70%) and oats (30%) oil (Protanal H 120)
This diet was supplemented with antibiotics and radioactive silver iodide in place of some cooked wheat and water, respectively. No supplemential vitamin or mineral levels were used.
DO ANTIBIOTICS AFFECT FEED INTAKE OF RAINBOW TROUT?
111
in each group were anaesthetized and the radioactivity from the ingested diet was counted for 2 x 10 s as described by Storebakken et al. ( 198 1) . The effect of the presence of OA or OTC in the medicated feed was tested by a nested model which includes the effect of drug and the effect of tank within drug. The effect of fish size within tank and treatment was tested by linear regression analysis. The counting results were corrected for background irradiation and decay. The amount of radioactive material ingested was calculated by means of the equation:
which was used by Storebakken et al. ( 198 1) . In this equation, F is the amount of radioactivity ingested (kBq) and M is the radioactivity counted under the fish stomach (counts/ 10 s). The feed intake was then calculated on the basis of the amount of radioactivity added to the feed. Repeated countings of the diets suggest that the radioactivity in the diets was distributed homogeneously (C.V. range, 1.5-3.6%) and that the instrument was stable during the experiments (C.V., 5.6%). RESULTS
The counting results measured for all fish (numbers of individual fish in each experiment given in Table 2) in the groups ranged from 0 to 400* lo3 counts/ 10 s and the corresponding feed intake was estimated to range from 0 to 4.4% of body weight. The results concerning intake of medicated feed and the control diet are presented in Table 2. The feed intake registrations showed that about 30% of the feed was rejected by the fish, confirming that feeding was in excess. TABLE 2 Intake of medicated feed during a 6-h feeding period Expt. no.
Drug
Fish weight (g) .f+ s.d.
No. of fish (n)
No. of tanks (n)
Feed intake (O/aof body weight ) m? s.d.
I
Control OA IOa OTC IOb
614+ 139 6302 142 638+ 177
36 35 34
2 2 2
2.09 + 0.43 1.73kO.37 0.81 to.35
2
OA I OA 10
3341- 87 327+ 81
54 56
3 3
1.13+0.41 1.17t0.45
“Oxolinic acid, g/kg feed. “Oxytetracycline. g/kg feed
112
SO. HUSTVEDT ET AL.
Supplements of OA in the diet tended to reduce mean feed intake (mean reduction 17%) compared to controls. This reduction was, however, not significant (P=O.O9). The ten-fold lower dietary concentration of OA used in Expt. 2 did not lead to feed intake which differed from that in Expt. 1. Addition of OTC resulted in a 6 1% reduction in feed intake (P-c 0.05 ) compared to controls. A considerable non-systematic variation in fed intake was seen. The coefficient of variation of the feed intake among fish within treatment ranged from 16.6% in the control group to 43.2% in the group fed with the diet with oxytetracycline. Weight of fish within treatment did not contribute significantly to the variation in feed intake expressed in g ( r2 = 0.0-O. 1) or % body weight (r* = 0.2-0.3). No significant effect of tank within treatment was seen. DISCUSSION
The reduced intake of medicated feed showed that the fish were rejecting a surprisingly high amount of the OTC diet, probably due to the unpalatability of the feed containing this drug. This was not as evident in fish fed the OA diet. It is worth noting that the amount of OA added to commercial medicated feed used in therapeutic treatment of bacterial infections is either 5 or 10 g/kg, which is within the range used in this study. In contrast, the amount of OTC added to commercial medicated feed is 100 g/kg, i.e. ten times higher than the amount added to the diet in this study. At low water temperatures, the amount of ingested feed declines, and the amount of drug in the feed has to be increased in order to obtain the therapeutic dosage. Our results indicate, however, that the consumption of OA would not be affected by the taste of the drug even at lower temperatures since the drug content would still be below 10 g/kg. A significant non-systematic variation in drug intake was evident. This variation masked the general effects of lish size on feed intake which were to be expected (reviewed by Brett, 1979; Brett and Groves, 1979). Our data do not offer any explanation of this variation, However, non-systematic variations in feed intake which are not explained by fish size and water temperature have previously been discussed by Storebakken and Austreng ( 1988a,b). In our experience, the isotope method used usually gives data with a considerably higher fish-to-fish variation than conventional studies on feed intake; a general discussion of this method has been given by Storebakken et al. (1981). When planning oral treatment regimens, it is important to be aware of the possible reduction of medicated feed intake due to the presence of distasteful drugs, and reduced consumption of medicated feed would adversely affect the efficacy of a given treatment. The non-systematic variation in our data limits the possibility of predicting medicated feed intake when antibiotics are
DO ANTIBIOTICS AFFECT FEED INTAKE OF RAINBOW TROUT?
113
added to the feed. The results, however, show that it may be advantageous to use a palatable drug, or to mask the taste of the drug, by encapsulation and/ or with an appetite enhancer, when the oral route of drug delivery is undertaken. ACKNOWLEDGEMENTS
The authors thank Olaug Kvendset, Vidar Vassvik and Georg 0stby for skillful technical assistance. This work was financially supported by the Norwegian Fisheries Research Council and the Agricultural Research Council of Norway.
REFERENCES Austreng, E., 1976. Fett og protein i for til laksefisk. 1. Fettinnhold i ternfor til lakseunger (Sulrno sakzr,L. ). Meld. Nor. Landbrukshsgsk., 55 (5), 16 pp. Brett, J.R., 1979. Environmental factors and growth. In: W.S. Hoar, D.J. Randall and J.R. Brett (Editors), Bioenergetics and Growth. Fish Physiology, Vol. 8. Academic Press, New York, NY. pp. 599-675. Brett, J.R. and Groves, T.D.D., 1979. Physiological energetics. In: W.S. Hoar, D.J. Randall and J.R. Brett (Editors), Bioenergetics and Growth. Fish Physiology, Vol. 8. Academic Press, New York, NY, pp. 279-352. Gutsell. J.L. and Snieszko, SF., 1949. Response of brook, rainbow, and brown trout to various dosages of sulfamerazine. Trans. Am. Fish. Sot., 77: 93-101. Ishiwata. N., 1968. Ecological studies on the feeding of fishes. IV. Satiation curve. Bull. Jpn. Sot. Sci. Fish., 34: 691-693. Schreck, J.A. and Moffttt, C.M., 1987. Palatability of feed containing different concentrations of erythromycin thiocyanate to chinook salmon. Prog. Fish-Cult., 49: 241-247. Snieszko. S.F. and Griffm, J.P., 1955. Kidney disease in brook trout and its treatment. Prog. Fish-Cult., 17: 3-l 3. Snieszko, S.F. and Wood, E.M., 1955. The effect of some sulfonamides on the growth of brook trout, brown trout, and rainbow trout. Trans. Am. Fish. Sot., 84: 86-92. Storebakken, T. and Austreng, E., 1988a. Feed intake measurements in fish using radioactive isotopes. I. Experiments with rainbow trout in fresh water. Aquaculture, 70: 269-276. Storebakken, T. and Austreng, E.. 1988b. Feed intake measurements in fish using radioactive isotopes. II. Experiments with Atlantic salmon and rainbow trout in sea-pens. Aquaculture. 70: 277-288, Storebakken, T., Austreng, E. and Steenberg, K., 1981. A method for determination of feed intake in salmonids using radioactive isotopes. Aquaculture, 24: 133-142.
109
Does oral administration of oxolinic acid or oxytetracycline affect feed intake of rainbow trout? Svein Olaf Hustvedt, Trond Storebakken and Ragnar Salte .4KlGfFOUSK (institute ofAquacuiture Research]. N-1432 &NLH,
Norway
(Accepted 30 May 1990)
ABSTRACT Hustvedt, S.O., Storebakken, T. and Salte, R., 1991. Does oral administration of oxolinic acid or oxytetracycline affect feed intake of rainbow trout? Aquaculture, 92: 109- 1 13. Short-term oral drug intake was measured in rainbow trout (Oncorhynchus mykiss) using radioactively labelled diets. In Experiment 1, duplicate groups of trout were fed either a control diet without antibiotic addition, or diets containing either 10 g oxolinic acid (OA) or IO g oxytetracycline (OTC) per kg. In Experiment 2, triplicate groups of trout were fed diets containing either 1 or 10 g OA per kg. The trout, weighing 200-900 g, were kept in freshwater at 10°C. The fish were accustomed to feeding to satiation every 20 min, 20 h/day; the drugs were fed over a 6-h period. The amount of radioactive feed ingested by the fish was measured directly on anaesthetized fish with a portable gamma scintillation counter. The results showed that OA in the diet tended to reduce mean feed intake (mean reduction 17%) compared to controls. This reduction was, however, not significant (P=O.O9). Addition of OTC led to a 61% reduction in feed intake (P
INTRODUCTION
Oxolinic acid (OA) and oxytetracycline (OTC) are frequently used in therapy of bacterial infections in aquaculture. The predominant way of administering these antibiotics to fish is systemic treatment via the diet. Thus, knowledge about the acceptance of the feed supplemented with an antibiotic is important for oral treatment regimens. Reduced compliance in drug therapy due to the presence of distasteful drugs is a well known problem both in human and in veterinary medicine. Reduced palatability of medicated feed has earlier been linked directly to the taste of the drug in tests with sulfa derivatives (Gutsell and Snieszko, 1949; Snieszko and Griffm, 195 5; Snieszko and Wood, 1955 ) as well as in a test with erythromycin thiocyanate (Schreck and Moffltt, 1987 ). The aim of this study was to test whether the presence of 0044-8486/91/$03.50
0 1991 -
Elsevier Science Publishers
B.V.
S.O. HUSTVEDT ET AL.
110
OA or OTC in the diet affected the feed intake of rainbow trout (Oncorhynthus mykiss). MATERIALS AND METHODS
This study consisted of two experiments which were undertaken at AKVAFORSK at Sunndalsora. Six groups of rainbow trout (Oncorhynchus mykiss) were kept in indoor 1-m’ libre-glass tanks which were each supplied with freshwater. The lish were all in good health, i.e. no clinical signs of diseases were seen. The photoperiod was 24 h/day. The water flow rates were approximately 10 l/min. Water sources and water quality is described by Austreng ( 1976). In Experiment 1 (Expt. 1 ), each group consisted of 35 fish weighing 628 + 15 1 g (means? s.d. ), and in Experiment 2 (Expt. 2 ), each group consisted of 55 fish weighing 330 + 85 g. The water temperature was maintained at 10 ? 1 ‘C for at least 3 weeks before and during the experimental period. Handling stress was reduced to a minimum in the experiments, and the environment to which the fish were accustomed was maintained since the farming environment may influence feed intake (Ishiwata, 1968) The fish were fed a commercial, dry pelleted diet until 3 weeks prior to the experiments. Then a moist diet was fed, which also served as the control diet (Table 1) . The moist diet was manufactured by using a meat mincer equipped with a 5-mm die. Fish were fed to satiation by automatic feeders every 20 min, 20 h/day. The trout were starved for 12 h before initiation of each experiment. Radioactive silver iodide ( Ag”‘I) was added to each of the diets at a level of 74 MBq/kg in both experiments. In Expt. 1, duplicate groups of trout were fed either the control diet without antibiotic incorporation, or the diet with either 10 g OA or 10 g OTC per kg. In Expt. 2, triplicate groups of trout were fed diets containing either 1 or 10 g OA per kg. Both OA and OTC were supplied by the Norwegian Medicinal Depot, Oslo, Norway. The medicated diets were fed every 20 min over a 6-h period. Then all fish TABLE 1 Formulation
of the moist control diet
Ingredients
g/kg
Capelin Cooked Capelin Alginate Water
367 180 107 13 333
meal (NorSeaMink) wheat (70%) and oats (30%) oil (Protanal H 120)
This diet was supplemented with antibiotics and radioactive silver iodide in place of some cooked wheat and water, respectively. No supplemential vitamin or mineral levels were used.
DO ANTIBIOTICS AFFECT FEED INTAKE OF RAINBOW TROUT?
111
in each group were anaesthetized and the radioactivity from the ingested diet was counted for 2 x 10 s as described by Storebakken et al. ( 198 1) . The effect of the presence of OA or OTC in the medicated feed was tested by a nested model which includes the effect of drug and the effect of tank within drug. The effect of fish size within tank and treatment was tested by linear regression analysis. The counting results were corrected for background irradiation and decay. The amount of radioactive material ingested was calculated by means of the equation:
which was used by Storebakken et al. ( 198 1) . In this equation, F is the amount of radioactivity ingested (kBq) and M is the radioactivity counted under the fish stomach (counts/ 10 s). The feed intake was then calculated on the basis of the amount of radioactivity added to the feed. Repeated countings of the diets suggest that the radioactivity in the diets was distributed homogeneously (C.V. range, 1.5-3.6%) and that the instrument was stable during the experiments (C.V., 5.6%). RESULTS
The counting results measured for all fish (numbers of individual fish in each experiment given in Table 2) in the groups ranged from 0 to 400* lo3 counts/ 10 s and the corresponding feed intake was estimated to range from 0 to 4.4% of body weight. The results concerning intake of medicated feed and the control diet are presented in Table 2. The feed intake registrations showed that about 30% of the feed was rejected by the fish, confirming that feeding was in excess. TABLE 2 Intake of medicated feed during a 6-h feeding period Expt. no.
Drug
Fish weight (g) .f+ s.d.
No. of fish (n)
No. of tanks (n)
Feed intake (O/aof body weight ) m? s.d.
I
Control OA IOa OTC IOb
614+ 139 6302 142 638+ 177
36 35 34
2 2 2
2.09 + 0.43 1.73kO.37 0.81 to.35
2
OA I OA 10
3341- 87 327+ 81
54 56
3 3
1.13+0.41 1.17t0.45
“Oxolinic acid, g/kg feed. “Oxytetracycline. g/kg feed
112
SO. HUSTVEDT ET AL.
Supplements of OA in the diet tended to reduce mean feed intake (mean reduction 17%) compared to controls. This reduction was, however, not significant (P=O.O9). The ten-fold lower dietary concentration of OA used in Expt. 2 did not lead to feed intake which differed from that in Expt. 1. Addition of OTC resulted in a 6 1% reduction in feed intake (P-c 0.05 ) compared to controls. A considerable non-systematic variation in fed intake was seen. The coefficient of variation of the feed intake among fish within treatment ranged from 16.6% in the control group to 43.2% in the group fed with the diet with oxytetracycline. Weight of fish within treatment did not contribute significantly to the variation in feed intake expressed in g ( r2 = 0.0-O. 1) or % body weight (r* = 0.2-0.3). No significant effect of tank within treatment was seen. DISCUSSION
The reduced intake of medicated feed showed that the fish were rejecting a surprisingly high amount of the OTC diet, probably due to the unpalatability of the feed containing this drug. This was not as evident in fish fed the OA diet. It is worth noting that the amount of OA added to commercial medicated feed used in therapeutic treatment of bacterial infections is either 5 or 10 g/kg, which is within the range used in this study. In contrast, the amount of OTC added to commercial medicated feed is 100 g/kg, i.e. ten times higher than the amount added to the diet in this study. At low water temperatures, the amount of ingested feed declines, and the amount of drug in the feed has to be increased in order to obtain the therapeutic dosage. Our results indicate, however, that the consumption of OA would not be affected by the taste of the drug even at lower temperatures since the drug content would still be below 10 g/kg. A significant non-systematic variation in drug intake was evident. This variation masked the general effects of lish size on feed intake which were to be expected (reviewed by Brett, 1979; Brett and Groves, 1979). Our data do not offer any explanation of this variation, However, non-systematic variations in feed intake which are not explained by fish size and water temperature have previously been discussed by Storebakken and Austreng ( 1988a,b). In our experience, the isotope method used usually gives data with a considerably higher fish-to-fish variation than conventional studies on feed intake; a general discussion of this method has been given by Storebakken et al. (1981). When planning oral treatment regimens, it is important to be aware of the possible reduction of medicated feed intake due to the presence of distasteful drugs, and reduced consumption of medicated feed would adversely affect the efficacy of a given treatment. The non-systematic variation in our data limits the possibility of predicting medicated feed intake when antibiotics are
DO ANTIBIOTICS AFFECT FEED INTAKE OF RAINBOW TROUT?
113
added to the feed. The results, however, show that it may be advantageous to use a palatable drug, or to mask the taste of the drug, by encapsulation and/ or with an appetite enhancer, when the oral route of drug delivery is undertaken. ACKNOWLEDGEMENTS
The authors thank Olaug Kvendset, Vidar Vassvik and Georg 0stby for skillful technical assistance. This work was financially supported by the Norwegian Fisheries Research Council and the Agricultural Research Council of Norway.
REFERENCES Austreng, E., 1976. Fett og protein i for til laksefisk. 1. Fettinnhold i ternfor til lakseunger (Sulrno sakzr,L. ). Meld. Nor. Landbrukshsgsk., 55 (5), 16 pp. Brett, J.R., 1979. Environmental factors and growth. In: W.S. Hoar, D.J. Randall and J.R. Brett (Editors), Bioenergetics and Growth. Fish Physiology, Vol. 8. Academic Press, New York, NY. pp. 599-675. Brett, J.R. and Groves, T.D.D., 1979. Physiological energetics. In: W.S. Hoar, D.J. Randall and J.R. Brett (Editors), Bioenergetics and Growth. Fish Physiology, Vol. 8. Academic Press, New York, NY, pp. 279-352. Gutsell. J.L. and Snieszko, SF., 1949. Response of brook, rainbow, and brown trout to various dosages of sulfamerazine. Trans. Am. Fish. Sot., 77: 93-101. Ishiwata. N., 1968. Ecological studies on the feeding of fishes. IV. Satiation curve. Bull. Jpn. Sot. Sci. Fish., 34: 691-693. Schreck, J.A. and Moffttt, C.M., 1987. Palatability of feed containing different concentrations of erythromycin thiocyanate to chinook salmon. Prog. Fish-Cult., 49: 241-247. Snieszko. S.F. and Griffm, J.P., 1955. Kidney disease in brook trout and its treatment. Prog. Fish-Cult., 17: 3-l 3. Snieszko, S.F. and Wood, E.M., 1955. The effect of some sulfonamides on the growth of brook trout, brown trout, and rainbow trout. Trans. Am. Fish. Sot., 84: 86-92. Storebakken, T. and Austreng, E., 1988a. Feed intake measurements in fish using radioactive isotopes. I. Experiments with rainbow trout in fresh water. Aquaculture, 70: 269-276. Storebakken, T. and Austreng, E.. 1988b. Feed intake measurements in fish using radioactive isotopes. II. Experiments with Atlantic salmon and rainbow trout in sea-pens. Aquaculture. 70: 277-288, Storebakken, T., Austreng, E. and Steenberg, K., 1981. A method for determination of feed intake in salmonids using radioactive isotopes. Aquaculture, 24: 133-142.