Chapter 2 Fish
TABLE 2-1 Antimicrobial and Antifungal Agents Used in Fish.a–f
| Agent | Dosage | Comments |
|---|---|---|
| Acriflavine | 4 mg/L × 4h78 | Rainbow trout/organic dye and antifungal agent |
| 10 mg/L × 4h73 | Channel catfish/PD | |
| Amikacin | 5 mg/kg IM q12h95 | |
| 5 mg/kg IM q72h × 3 treatments105 | ||
| 5 mg/kg ICe q24h × 3 days, then q48h × 2 treatments49 | Koi/PD | |
| Amoxicillin | — | Infrequently indicated in ornamental fish because few pathogens are Gram-positive |
| 12.5 mg/kg IM4 | Atlantic salmon/PD | |
| 25 mg/kg PO q12h97 | ||
| 40 mg/kg IV q24h18 | Seabream/PD | |
| 80 mg/kg PO q24h × 10 days18 | Seabream/PD | |
| 40-80 mg/kg/day in feed × 10 days67 | ||
| 110 mg/kg/day in feed1 | Channel catfish/PD | |
| Ampicillin | — | Infrequently indicated in ornamental fish because few pathogens are Gram-positive |
| 10 mg/kg q24h IM4,102 | ||
| 10 mg/kg q24h IV71 | Striped bass | |
| 50-80 mg/kg/day in feed × 10 days67 | ||
| Azithromycin (Zithromax, Pfizer) | 30 mg/kg q24h × 14 days22 | Chinook salmon/PD |
| 40 mg/kg ICe23 | Chinook salmon/PD | |
| Aztreonam (Azactam, Squibb) | 100 mg/kg IM, ICe q48h × 7 treatments80 | Koi/Aeromonas salmonicida; used by hobbyists |
| Benzalkonium chloride | 0.5 mg/L long-term102 | Quaternary amine with broad disinfection properties |
| 10 mg/L for 10 min102 | ||
| Bronopol (Pyceze, Novartis) | 15-50 mg/L × 30-60 min bath75,105 | For mycotic infections (eggs and fish); eggs may require the higher dose |
| Ceftazidime (Fortaz, Pfizer) | 22 mg/kg IM, ICe q72-96h × 3-5 treatments80 | Cephalosporin with good activity against Gram-negative bacteria (e.g., Pseudomonas) |
| Chloramine-T | 2.5-20 mg/L as immersion treatment15,102 | Disinfectant; used to control bacterial gill disease and some ectoparasites; dosage and duration varies widely with species and water quality |
| 20 mg/L as immersion × 4 hr64 | Rainbow trout, striped bass, yellow perch/PD | |
| Chloramphenicol | — | Florfenicol may be a better alternative than chloramphenicol (risk to humans) |
| 40-182 mg/kg q24h ICe54 | Carp/PD | |
| 50 mg/kg PO, IM once, then 25 mg/kg q24h97 | ||
| 50 mg/kg PO q24h13 | Rainbow trout/PD | |
| Ciprofloxacin | 15 mg/kg IM, IV69 | Carp, African catfish, rainbow trout/PD |
| Conazole (Prochloraz) | 10 mg/kg PO q24h12 | Rainbow trout/antifungal |
| Difloxacin | 10 mg/kg PO q24h21 | Atlantic salmon/PD; plasma levels were higher in marine fish compared with freshwater fish |
| 20 mg/kg PO q24h × 3 days19 | Goldfish/PD | |
| Enrofloxacin (Baytril, Bayer) | — | For a review of quinolones used in fishes see Samuelsen, 200684 |
| 2.5 mg/kg IV q24h17 | Seabream/PD; no ciprofloxacin detected | |
| 5 mg/kg PO, IM, ICe q24h97 | Red pacu/PD62 | |
| 5-10 mg/kg PO q24h102 | ||
| 5-10 mg/kg IM, ICe q48h62× 7 treatments | ||
| 10 mg/kg PO q24h17,84 | Atlantic salmon, seabream/PD; no ciprofloxacin detected | |
| 10 mg/kg PO, IV52 | Korean catfish/PD; ciprofloxacin detected | |
| 10 mg/kg ICe q96h × 4 treatments61 | Koi/PD (21°C, 70°F) | |
| 10 mg/kg PO in feed q24h57,67,94 | Atlantic salmon/PD | |
| 0.1% feed × 10-14 days | Oral or injectable form can be used | |
| 2.5-5 mg/L × 5 hr bath q24h62× 5-7 days | Red pacu/PD; change 50-75% of water between treatments | |
| Erythromycin | — | Commonly sold as tank treatment for aquarium fish; not recommended because of toxicity to nitrifying bacteria67 |
| 75 mg/kg PO q24h × 7 days14 | Barramundi/successful treatment of Streptococcus iniae | |
| 100 mg/kg PO, IM q24h × 7-21 days97,102 | ||
| 100-200 mg/kg PO q24h × 21 days65 | Salmonids/to control Renibacterium salmoninarum | |
| Florfenicol (Nuflor, Schering Plough) | 5-20 mg/kg PO q24h44 | Atlantic salmon/PD |
| 10 mg/kg IM q24h110,111 | Koi/PD | |
| 10-20 mg/kg PO q24h85,88 | Cod/PD | |
| × 10 days | ||
| 25-50 mg/kg PO q24h110,111 | Koi/PD | |
| 40 mg/kg IM112 | White-spotted bamboo shark/PD | |
| 40-50 mg/kg PO, IM, ICe q12-24h60,97 | Red pacu/PD60 | |
| 100 mg/kg IM q24h110,111 | Gourami/PD | |
| Flumequine (Apoquin aqualtes, Alpharma) | — | Quinolone; Gram-negative bacteria; freshwater fish at pH 6.8-7.2; decreased uptake in hard water; increase dose for marine fish |
| 10 mg/kg PO q48h34 | Cod, goldsinny wrasse/PD | |
| 12-25 mg/kg PO, ICe, IV q24h86 | Atlantic halibut/PD | |
| 25 mg/kg ICe q24h87 | Corkwing wrasse/PD | |
| 25-50 mg/kg PO q24h82 | Atlantic salmon | |
| 30 mg/kg IM, ICe67 | High antibiotic levels for several days when given IM | |
| 50-100 mg/L × 3 hr bath67 | ||
| 10 mg/kg q24h in feed × 10 days67 | ||
| Formalin | All doses based on volumes of 100% formalin (= 37% formaldehyde) | Mycotic infections on eggs; do not treat within 24 hr of hatching; caution: carcinogenic; do not use if highly toxic white precipitates of paraformaldehyde are present; some fish are very sensitive; test on small number first, monitor fish for respiratory distress and pale color; increased toxicity in soft, acidic water and at high temperature; treat with vigorous aeration because of oxygen depletion; toxic to plants |
| 0.23 mL/L bath up to 60 min67 | ||
| 1 mL/38 L as 12-24 hr bath followed by 30-70% water change, may be repeated28 | ||
| 1-2 mL/L bath, up to 15 min67 | For eggs only | |
| 25 mg/L (9.3 mg formaldehyde/L) bath for 144 hr108 | Striped bass | |
| Furazolidone | — | Nitrofuran; caution: carcinogenic; toxic to scaleless fish; absorbed from water; drug inactivated in bright light |
| 1 mg/kg PO, IV q24h72 | Channel catfish | |
| 30 mg/kg PO109 | Nile tilapia | |
| 67.5 mg/kg PO q12h × 10 days55 | Rainbow trout/PD; at 14°C (57°F), half-life  30 days and residue present at 40 days post 10-day treatment | |
| 25-35 mg/kg q24h in feed for 20 days42 | Some salmonids/not approved for fish intended for human consumption in the United States | |
| 50-100 mg/kg q24h in feed × 10-15 days67 | ||
| 1-10 mg/L tank water for ≥ 24 hr67 | ||
| Gentamicin | 1 mg/kg IM, ICe q24h91 | Channel catfish/PD |
| 2 mg/kg IM, then 1 mg/kg IM at 8 and 72 hr98 | Brown shark/PD | |
| 2.5 mg/kg IM q72h58 | Nephrotoxic; substantial risk in species for which dosages have not been determined77 | |
| 3.5 mg/kg IM q24h50 | Goldfish, toadfish/PD | |
| Iodine, potentiated (Betadine, Purdue Frederick) | ||
| Itraconazole | 1-5 mg/kg q24h in feed q1-7d97 | Systemic mycoses |
| Kanamycin sulfate (Kantrex, Adothecon) | 20 mg/kg ICe q3d × 5 treatments67 | Toxic to some fish |
| 50 mg/kg q24h in feed67 | ||
| 40-640 mg/L × 2 hr bath26 | Channel catfish | |
| 50-100 mg/L q72h × 3 treatments67 | Change 50-75% of water between treatments; absorbed from water | |
| Ketoconazole | 2.5-10 mg/kg PO, IM, ICe97 | Systemic mycoses |
| Malachite green (zinc-free) | — | Freshwater fish/mycotic infections; caution: mutagenic, teratogenic; toxic to some fish species and to fry; increased toxicity at higher temperatures and lower pH; stains objects, especially plastic; toxic to plants; not approved for use on fish intended for human consumption |
| 0.1 mg/L tank water q3d × 3 treatments67 | Remove residual chemical with activated carbon after final treatment | |
| 0.25 mg/L × 15 min q24h106 | Fungal control on fish eggs | |
| 0.5 mg/L × 1 hr bath67 | Freshwater fish eggs | |
| 1 mg/L × 30-60 min bath67 | Use 2 mg/L if pH is high | |
| 1 mg/L × 1 hr102 | Fungal control on fish eggs | |
| 2 mg/L × 15 min q24h102 | Fungal control on fish eggs | |
| 10 mg/L × 10-30 min bath67 | Freshwater fish eggs | |
| 50-60 mg/L × 10-30 sec bath67 | ||
| 100 mg/L topical to skin lesions67 | ||
| Methylene blue | 2 mg/L tank water q48h, up to 3 treatments67 | Preventing infections of freshwater eggs; toxic to nitrifying bacteria and to plants; stains many objects |
| Miconazole (Monistat, Janssen) | 10-20 mg/kg PO, IM, ICe97 | Systemic mycoses |
| 20 mg/kg PO q24h102 | ||
| 13 mg/L × 1-4 hr bath, repeat prn67 | ||
| Neomycin | 66 mg/L tank water q3d, up to 3 treatments67 | Commonly sold as tank treatment for aquarium fish; toxic to nitrifying bacteria; keep fish densities low |
| Nifurpirinol | — | Nitrofuran; caution: carcinogenic; toxic to scaleless fish; absorbed from water; drug inactivated in bright light |
| 0.45-0.9 mg/kg PO q24h × 5 days67 | ||
| 4-10 mg/kg in feed q12h × 5 days68 | ||
| 0.1 mg/L tank water q24h × 3-5 days67 | ||
| 1-2 mg/L × 5 min-6 hr bath67 | ||
| Nitrofurazone | — | Nitrofuran; caution: carcinogenic; toxic to scaleless fish; absorbed from water; drug inactivated in bright light; water soluble formulations preferred; change 50-75% of water between treatments |
| 2-5 mg/L tank water q24h × 5-10 days105 | ||
| 50 mg/L × 3 hr9 | Seabream/no residues were found in muscle following treatment | |
| 100 mg/L × 30 min bath67 | ||
| 100 mg/L × 6 hr9 | Tilapia/no residues were found in muscle following treatment | |
| Oxolinic acid | — | Quinolone; Gram-negative bacteria |
| 5-25 mg/kg PO q24h97 | ||
| 10 mg/kg q24h PO102 | Freshwater species/PD in many species | |
| 25 mg/kg ICe q24h87 | Corkwing wrasse/PD | |
| 25-50 mg/kg q24h PO102 | Marine species | |
| 50 mg/kg q24h × 5 days PO10,11 | Rainbow trout/PD | |
| 10 mg/kg q24h in feed × 10 days67 | ||
| 3-10 mg/L tank water × 24 hr67 | ||
| 25 mg/L × 15 min bath q12h × 3 days67 | Decreased uptake in hard water; better uptake in pH <6.9 | |
| Oxytetracycline | 3 mg/kg IV q24h20 | Red pacu/PD |
| 7 mg/kg IM q24h20 | Red pacu/PD | |
| 10 mg/kg IM q24h97 | Produces high levels for several days when given IM | |
| 20 mg/kg ICe102 | Some salmonids | |
| 20 mg/kg PO q8h97 | ||
| 25-50 mg/kg IM, ICe67 | ||
| 60 mg/kg IM q7d30 | Carp/PD | |
| 70 mg/kg PO q24h × 10-14 days104 | ||
| 82.8 mg/kg PO × 10 days8 | Walleye pike, tilapia, hybrid striped bass, summer flounder/PD | |
| 100 mg/kg IM q24h79 | Tench/PD | |
| 10-100 mg/L tank water67 | Higher doses in hard water; if fish still sick, retreat on day 3 after 50% water change; light sensitive, so keep tank covered to prevent photo-inactivation; drug turns dark brown when decomposing: change 50% of water immediately; change 50-75% of water between treatments | |
| 7 mg/g feed q24h × 10 days104 | ||
| 55-83 mg/kg q24h in feed × 10 days67 | ||
| 75 mg/kg PO q24h in feed × 10 days102 | ||
| 10-50 mg/L × 1 hr bath67 | Surface bacterial infections; yellow-brown foam may develop in treatment water | |
| Potassium permanganate | 2 mg/L as an indefinite bath105 | Heavily organic systems may require a higher dose; test efficacy by adding the appropriate amount of KMnO4 to a small amount of system water (without fish); red color should remain for at least 4 hr (if not, then KMnO4 should be added until the 4-hr test is completed) |
| 5 mg/L × 30-60 min bath67 | Freshwater fish/skin and gill bacterial infections; toxic in water with high pH; do not mix with formalin; can be toxic in goldfish95 | |
| 1000 mg/L × 10-40 sec bath67 | ||
| Sarafloxacin (Saraflox, Abbott) | 10-14 mg/kg PO q24h × 10 days97 | Fluoroquinolone |
| 10 mg/kg PO q24h102 | Marine Atlantic salmon | |
| 10 mg/kg PO q24h × 5 days27 | Channel catfish | |
| Silver sulfadiazine cream (Silvadene, Marion Merrill Dow) | Topical q12h58 | External bacterial infection; keep lesion out of water 30-60 sec after application; keep gills submerged |
| Sulfadimethoxine/ormetoprim (Romet, Hoffman-LaRoche) | ||
| Thiamphenicol | 15 and 30 mg/kg PO45 | Sea bass/PD; drug was not detected in plasma or tissues at either dose on day 7; recommended withdrawal times of 5 and 6 days, respectively |
| Tobramycin | 2.5 mg/kg IM, then 1 mg/kg IM q4d98 | Brown shark/PD |
| Trimethoprim/sulfamethoxazole | 30 mg/kg PO q24h × 10-14 days67 | Change 50-75% of water between treatments |
| 20 mg/L × 5-12 hr bath q24h × 5-7 days67 | ||
| 0.2% feed × 10-14 days67 | ||
| Triple antibiotic ointment (polymyxin B sulfate/bacitracin/neomycin sulfate) | Topical q12h58 | External bacterial infection; keep lesion out of water 30-60 sec following application; keep gills submerged |
a Not to be used in fish for human consumption.
b Preferable to treat a single fish of a species (biotest) to determine toxicity.
c Tank treatment: When treating the fishes’ resident aquarium, disconnect activated carbon filtration to prevent drug removal. Many drugs adversely affect the nitrifying bacteria, so water quality should be monitored closely (especially ammonia and nitrite concentrations). Always keep water well aerated and monitor fish closely. Perform water changes and reconnect filtration to remove residual drug following treatment. Discard carbon following drug removal.59
d Bath (immersion) treatment: Remove fish from resident aquarium and place in container with known volume of water and concentration of therapeutic agent. Watch closely for signs of toxicity (e.g., listing and dyspnea). Always keep water well aerated.
e Species of fish, temperature, and water quality parameters can influence the pharmacodynamics of many drugs, especially antimicrobials.
f For more information, refer to the web site by Reimschuessel et al.78 This is a comprehensive and informative resource for many drugs and other compounds used with aquatic animals.
TABLE 2-2 Antiparasitic Agents Used in Fish.a–d
| Agent | Dosage | Comments |
|---|---|---|
| Acetic acid, glacial | 1-2 mL/L × 30-45 sec bath67,105 | Monogenean trematodes, crustacean ectoparasites; safe for goldfish; may be toxic to smaller tropical fish |
| Albendazole | 5 mg/kg PO once66 | Atlantic salmon/PD |
| 10 mg/kg PO once92 | Atlantic salmon, rainbow trout, tilapia/PD | |
| 10-50 mg/L × 2-6 hr90 | Sticklebacks/treating Glugea anomala infection | |
| Chloramine-T | — | See Table 2-1 |
| Chloroquine diphosphate | ||
| Closantel (50 mg/mL)/mebendazole (75 mg/mL) (Supaverm, Janssen) | 1 mL/400 L once; may repeat in 3-7 days following a water change if necessary105 | Very safe and effective in koi for external monogeneans; reported to be highly toxic to goldfish and medaka; used in the United Kingdom to kill digenean trematodes of sheep |
| Copper sulfate | — | Marine fish/protozoan, trematode ectoparasites; copper levels must be assessed with a commercial kit, and adjusted as needed; toxic to gill tissue; immunosuppressive; extremely toxic to invertebrates and many plants; copper removed by activated carbon |
| 0.012 and 0.094 mg/L bath for 28 days31 | European eel | |
| 0.02 mg/L bath × 65 or 72 hr32,33 | Rainbow trout | |
| 0.1-0.2 mg/L102 | Use higher dose in hard water | |
| Maintain free ion levels at 0.15-0.2 mg/L tank water, until therapeutic effect67 | ||
| Maintain copper levels at 0.2 mg/L tank water × 14-21 days104 | Citrated copper sulfate; prepare stock solution of 1 mg/mL (3 g CuSO4 · 5H2O and 2 g citric acid monohydrate in 750 mL distilled water) | |
| Maintain free ion levels at 0.25-1 mg/L × 24-48 hr bath36 | ||
| 100 mg/L × 1-5 min bath7 | Prepare stock solution of 1 mg/mL (1 g CuSO4 · 5H2O in 250 mL distilled water) | |
| Diflubenzuron (Dimilin, Union Carbide) | 0.01 mg/L tank water × 48 hr q6d × 3 treatments95 | Crustacean ectoparasites; inhibits chitin synthesis; drug persists in water long-term; marketed for control of terrestrial insects; may need EPA license for use in the United States |
| Dimethyl phosphonate | — | See trichlorfon |
| Dimetridazole | 28 mg/kg in feed q24h × 10 days76 | Rainbow trout/Ichthyophthirius multifiliis; not available in United States |
| Enamectin (Slice, Schering Plough) | 50 μg/kg q24h × 7 days PO89 | Atlantic salmon/PD; an avermectin compound used to control sea lice (Lepeophtheirus salmonis, Caligus elongatus, C. teres, and C. rogercressyi) |
| Fenbendazole | 1 mg/kg IV16 | Channel catfish |
| 5 mg/kg PO × 1 dose53 | Channel catfish | |
| 6 mg/kg q24h PO47 | Rainbow trout | |
| 50 mg/kg PO q24h × 2 days, repeat in 14 days104 | ||
| 0.2% in feed × 3 days, repeat in 14-21 days57 | ||
| 40 mg/kg in feed q4d × 2 treatments102 | Carp/Bothriocephalus acheilognathi | |
| 1.5 mg/L × 12-hr bath47 | Rainbow trout | |
| 2 mg/L tank water q7d × 3 treatments67 | Nonencysted gastrointestinal nematodes | |
| 2.5 mg/g feed × 2-3 days, repeat in 14 days104 | ||
| Medicated brine shrimp, feed 2 consecutive days and repeat in 14 days104 | Place live brine shrimp in 400 mg fenbendazole per 100 mL water × 15-20 min, immediately before feeding to fish | |
| Formalin | — | Formalin combination follows |
| All doses based on volumes of 100% formalin (= 37% formaldehyde) | Protozoan, trematode, crustacean ectoparasites; caution: carcinogenic; do not use if highly toxic white precipitates are present; some fish are very sensitive: test on small number first, monitor for piping and pale color; increased toxicity in soft, acidic water and at high temperature; treat with vigorous aeration because of oxygen depletion; toxic to plants | |
| 0.015-0.025 mL/L tank water67 | For Ichthyophthirius, use 0.025 mL/L tank water q48h × 3 treatments; change up to 50% of water on alternate days | |
| 0.125-0.25 mL/L, up to 60 min bath, repeat q24h × 2-3 days prn67 | When using maximum dose, treat q3d | |
| 0.4 mL/L up to 1 hr bath q3d, up to 3 treatments95 | Soft water | |
| 0.5 mL/L up to 1 hr bath q3d, up to 3 treatments95 | Hard water | |
| Formalin (F)/malachite green (M) | (F) 0.025 mL/L + (M) 0.1 mg/L tank water q48h × 3 treatments67 | Combination synergistic for Ichthyophthirius; change up to 50% water on alternate days; several premixed commercial products available; malachite green should never be used on fish intended for human consumption |
| Freshwater | 3-15 min bath, repeat q7d prn67 | Marine fish/ectoparasites; aerate well; monitor closely; some small fish are sensitive |
| 4-5 min bath57 | ||
| Hydrogen peroxide (3%) | 1-1.5 mg/L × 20 min bath101 | Atlantic salmon/sea lice |
| 17.5 mL/L × 4-10 min bath, once36 | Ectoparasites; monitor closely; may be harmful to smaller fish | |
| Ivermectin | — | Do not use; neurologic signs and death at therapeutic doses;36,102 toxic to many environmental invertebrates102 |
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