Cutaneous antibodies in excised skin from channel catfish, Ictalurus punctatus Rafinesque, immune to Ichthyophthirius multifiliis

This study determined whether cutaneous antibodies were present in the excised skin of channel catfish, Ictalurus punctatus Rafinesque, immune to Ichthyophthirius multifiliis Fouquet (Ich). Theronts were immobilized on or near the excised skin from immune fish. The survival of immobilized theronts was significantly reduced after exposure for 8 h to the culture of excised skin from immune fish. Culture fluids from excised skin of immune fish immobilized theronts with a peak in the immobilization titre at 24 h post-exposure. Immobility of theronts in the culture fluid from immune skin was removed after immunoabsorption with theronts. Indirect immunofluorescent staining of theronts treated with culture fluid from excised skin of immune fish revealed strong and uniform fluorescence on the cilia and cell surface of theronts. Western blot analysis of the culture fluid from immune fish revealed a 70-kDa band which corresponded to the molecular weight of catfish immunoglobulin heavy chain. The results of this study show that cutaneous antibodies to Ich theronts were present in and released from the excised skin from fish immune to Ich. Immobilization and killing of the theronts are two characteristics of the antibody response that appear to prevent the successful invasion of theronts into excised skin.     

Cutaneous antibodies from channel catfish, Ictalurus punctatus (Rafinesque), immune to Ichthyophthirius multifiliis (Ich) may induce apoptosis of Ich theronts

This study explored the existence of apoptosis (programmed cell death) in Ichthyophthirius multifiliis Fouquet (Ich) theronts and determined the effect of cutaneous antibodies in skin culture fluid from fish immune to Ich on theront apoptosis. Apoptosis was detected in theronts and was clearly distinguished by fluorescent microscopy after staining with acridine orange and propidium iodide. The apoptotic theronts showed characteristic chromatin condensation and nuclear fragments containing chromatin pieces. The externalization of phosphatidylserine on the plasma membrane of apoptotic theronts was detected with fluorescein isothiocyanate-conjugated annexin using flow cytometry. Theront apoptosis was induced using the skin culture fluid from fish immune to Ich, which contained cutaneous antibodies against Ich. The highest apoptosis appeared in theronts exposed to immune skin culture fluid at a 1:10 dilution, compared with those at 1:20 and 1:40 dilutions. A direct correlation was noted between the percentage of apoptotic theronts and exposure duration to immune skin culture fluid. The study indicated that antibody reaction with theronts (immobilization) played an important role in theront apoptosis, but it could not be excluded that other components released from the excised skin had effects on theronts.     

Protective effect of cutaneous antibody produced by channel catfish,Ictalurus punctatus (Rafinesque), immune to Ichthyophthirius multifiliis Fouquet on cohabited non-immune catfish

Fish which survive a sublethal ichthyophthiriasis acquire protective immunity against Ichthyophthirius multifiliis Fouquet (Ich). This study evaluated the protective effect of cutaneous antibody secreted by channel catfish, Ictalurus punctatus (Rafinesque), immune to Ich on cohabited non-immune catfish. Non-immune and immune fish controls were separately maintained and infected with theronts. The Ich infection was assessed by scoring 0, < 50, 50-100, and > 100 trophonts fish(-1) at 5 days post-infection. The results of infection showed that cohabited fish at the ratio of 15 non-immune to two immune fish had < 50 trophonts fish(-1). Eighty per cent of the cohabited fish at the ratio of 10 non-immune to two immune fish showed 0 or < 50 trophonts fish(-1). The 76% of control non-immune fish had more than 100 trophonts fish(-1). The control immune fish had 0 trophonts fish(-1). Anti-Ich antibody was detected using enzyme-linked immunosorbent assay in water samples taken from tanks containing immune fish after the water samples were concentrated 40-fold. The study suggests that immune fish cohabited with non-immune fish may protect non-immune fish against Ich infection.     

Induced cross-protection in channel catfish, Ictalurus punctatus (Rafinesque), against different immobilization serotypes of Ichthyophthirius multifiliis

Abstract Channel catfish, Ictalurus punctatus (Rafinesque), were immunized with Ichthyophthirius multifiliis (Ich) theronts and trophonts, and the immune response and host protection against both homologous and heterologous serotypes of Ich were evaluated. Immunizations were done with two immobilization serotypes (ARS4 and ARS6) of live theronts by bath immersion (trial I) and with sonicated trophonts by intraperitoneal (i.p.) injection (trial II). Cutaneous and serum antibody titres against Ich following immunization were measured and survival of catfish was determined after theront challenge. Theronts were immobilized by the antiserum from fish immunized with homologous theronts or trophonts, but not by the serum of fish immunized with the heterologous serotype. Serum from fish immunized by immersion with live theronts showed higher enzyme-linked immunosorbent assay titres against both homologous and heterologous serotypes than fish immunized by i.p. injection of trophonts. Channel catfish immunized by immersion with live theronts or by i.p. injection with sonicated trophonts developed an immune response against Ich and provided cross-protection against challenge from both serotypes (ARS4 and ARS6) of the parasite. Sonicated trophont antigens in aqueous solution by i.p. injection could stimulate an immune response in fish, but the immunity was of short duration.     

Immune responses and host protection of channel catfish, Ictalurus punctatus (Rafinesque), against Ichthyophthirius multifiliis after immunization with live theronts and sonicated trophonts

The humoral immune responses and host protection of channel catfish, Ictalurus punctatus (Rafinesque), against Ichthyophthirius multifiliis (Ich) were determined after immunization with live theronts and sonicated trophonts. Immunizations with live theronts or sonicated trophonts were carried out by both bath immersion and intraperitoneal (i.p.) injection. Cutaneous and serum immunoglobulin (Ig) levels and anti-Ich antibodies were measured 12 and 21 days post-immunization. The level of Ich infection and survival of catfish were determined after theront challenge. Cutaneous and serum anti-Ich antibodies were significantly higher (P < 0.05) in fish immunized with live theronts by immersion or i.p. injection, or with sonicated trophonts administered by i.p. injection, than in fish immunized with sonicated trophonts by immersion, with bovine serum albumin by i.p. injection, or non-immunized controls. Host protection was noted only in fish immunized with live theronts by immersion or i.p. injection or with sonicated trophonts by i.p. injection. There was a positive correlation between higher levels of anti-Ich antibodies and host survival in the immunized fish.     

Protective Immunity of Goldfish Against Ichthyophthirius multifiliis Infection Induced by Different Trophont Vaccine Preparations

Ichthyophthirius multifiliis, commonly called “Ich,” is a protozoan parasite that infects the epidermis and gills of freshwater fish. Here, we used goldfish (Carassius auratus) to determine whether the four vaccine preparations (live trophonts, formalin‐fixed trophonts, freeze‐thawed trophont lysates, and trophont cilial and cell cortical fractions) of I. multifiliis (Fouquet) can elicit resistance of immunized fish against subsequent theront challenge, and whether a relationship exists between in vitro immobilization of theronts in sera or mucus from immunized fish and host protective immunity against the parasite. Experimental goldfish were randomly divided into five groups with five parallel controls, with each group or subgroup consisting of 20 individuals. Each test goldfish was immunized with one of the four Ich vaccine preparations administered by one of the three routes: live trophonts by gavage (Group 1), formalin‐fixed trophonts by injection (Group 2) or by immersion (Group 3), freeze‐thawed trophont lysates by injection (Group 4), and trophont cilial and cell cortical fractions by injection (Group 5). The fish were then challenged by a standard Ich theront challenge on Day 21 postimmunization. For every 10 d following immunization, we tested the in vitro immobilization of Ich theronts by sera or mucus from immunized and control fish. We found that although all control (nonimmunized) and Group 3‐immunized goldfish died following theront challenge, more than half (55–65%) of the immunized fish from Groups 1, 2, 4, and 5 survived. Furthermore, except for the fish from Groups 3 and 4, the number of mean days to death in each test group was significantly higher than that in the respective control. These results indicate that goldfish immunized by injection or by gavage with any of the four vaccine preparations gained resistance to Ich infection. Further analysis indicated that this protective immunity was closely associated with the in vitro immobilization of Ich theronts by fish sera or mucus.     

Ichthyophthiriasis in carp, Cyprinus carpio L.: fate of parasites in immunized fish

Abstract. The host-parasite relationship between O-group carp and the ciliatc Ichthyophthirius multifiliis Fouquet was investigated, with the specific aim of characterizing the fate of parasites encountering immunized fish. Carp were immunized by repeated controlled infections; immunized fish and control fish naive to I. multifiliis were then infected in the caudal fin epidermis by a single controlled exposure to theronts, which were applied in a droplet suspension to the tail surface. The number of parasites present within the caudal fin was monitored over a subsequent 5-day period by means of in situ parasite mapping. Results indicated that, contrary to previous reports, theronts penetrated the skin of immunized fish in numbers comparable to those of fish receiving a primary infection. However, the majority of parasites which penetrated immune skin did not complete normal development; 79% of the parasites which had initially penetrated the immune skin were not relocated within 2h of exposure, and since no parasite material was detected at penetration sites, it was concluded that these parasites had prematurely exited the skin rather than been killed in situ. Subsequently, these sites became populated by leucocytes, predominantly macrophages, and the infiltrations continued for up to 5 days after the initial exposure. In contrast, at sites where mature trophonts had exited the skin of fish following a primary infection, more diffuse leucocytic infiltrations were recorded, and these were predominated by neutrophils. Differences in the response to parasite exit from immunized and previously unexposed control fish skin are discussed, with particular reference to the mode of protection and the fate of parasites encountering immune fish.     

Susceptibility of three strains of blue catfish,Ictalurus furcatus (Valenciennes), to Ichthyophthirius multifiliis

This study compared the susceptibility of three blue catfish strains (D&B, USDA 101 and USDA 102) to the parasite Ichthyophthirius multifiliis (Ich). In Trial I, a cohabitation study (all strains stocked communally) was conducted and fish were exposed to theronts at 0, 200, 1000, 5000 or 25 000 theronts fish^?1, respectively. All fish died when exposed to theronts at 5000 or 25 000 theronts fish^?1. When exposed to 1000 theronts fish^?1, USDA 102 strain of blue catfish showed significantly lower mortality (78.5%) compared to USDA 101 and D&B strains (92.7% and 100%). In Trial II, the same three strains of blue fish were evaluated for their susceptibility to Ich with strains challenged in separate tanks by adding Ich theronts at 0, 200 and 1000 theronts fish^?1, respectively. All D&B and USDA 101 blue catfish died; however, 42.3% of USDA 102 strain survived the infection when exposed to 1000 theronts per fish. The results indicate that there are differences among strains of blue catfish for susceptibility to Ich, and these differences will be useful in the development of improved catfish germplasm for commercial aquaculture.     

Apoptosis in Ichthyophthirius multifiliis is associated with expression of the Fas receptor of theronts

The expression of type I membrane Fas receptors on the surface of Ichthyophthirius multifiliis (Ich) theronts and the possible association between Fas expression and theront apoptosis induced by the immune antibody was examined. Fas receptors were detected on the theront surface using fluorescein isothiocyanate-conjugated mouse monoclonal antibody against Fas. Fas-positive theronts significantly increased with time during in vitro incubation and with increasing theront concentration. Furthermore, the immune cutaneous antibody induced theront apoptosis; however, Fas ligand did not. A highly significant correlation was noted between theront Fas expression and immune cutaneous antibody-induced theront apoptosis. Numbers of apoptotic theronts increased with increasing number of Fas-positive theronts. The data indicated that theront apoptosis induced by immune cutaneous antibody appears to be positively correlated with the expression of Fas on the surface of Ich theronts.     

Ichthyophthirius multifiliis: standardization of the infection-response model in Ameca splendens (Miller & Fitzsimons)

Abstract. The goodeid fish Ameca splendens (Miller & Fitzsimons) was exposed to the parasite Ichthyophthirius multifiliis . Exposure levels were 2000,3000,6000 and 12000 theronts per fish. After 3 days, infection levels were determined and the body area of the fish was measured. A rise in the number of trophozoites per fish was observed, up to a level of 6000 theronts per fish. Standardization of infection and response by area, to theronts per square centimetre and trophozoites per square centimetre respectively, produced a significant linear relationship, up to an exposure of 2800 theronts per square centimetre, and also removed the between-tank within-dose variation. The measures of controlling exposure to 1. multifiliis and evaluating response in previous research are reviewed. Adoption of the technique described here will facilitate the collation of research on ichthyophthiriasis by permitting comparisons of different studies utilizing different sizes and species of fish.     

多子小瓜虫滋养体糖蛋白残基的种类和分布研究

应用伴刀豆凝集素A、麦胚凝集素、大豆凝集素和荆豆凝集素Ⅰ,检测寄生于金鱼皮肤、鳃和鳍上的多子小瓜虫滋养体糖蛋白残基的种类和分布。研究结果发现,伴刀豆凝集素A和麦胚凝集素免疫阳性染色在金鱼皮肤、鳃和鳍寄生的滋养体上均有分布,麦胚凝集素免疫阳性染色强于伴刀豆凝集素A,未见有大豆凝集素和荆豆凝集素Ⅰ免疫阳性染色。鳃上寄生的滋养体伴刀豆凝集素A免疫阳性染色最强,皮肤次之,鳍最弱。鳍上寄生的滋养体麦胚凝集素免疫阳性染色最强,皮肤次之,鳃最弱。研究结果表明,滋养体有单糖D-甘露糖和D-葡萄糖,以及氨基衍生物乙酰氨基葡萄糖。寄生于鳃上的滋养体D-甘露糖和D-葡萄糖可能较多,寄生在鳍上的滋养体乙酰氨基葡萄糖可能较多。     

鱼类抗刺激隐核虫感染的黏膜免疫研究进展

刺激隐核虫是一种原生纤毛类寄生虫,可以感染几乎所有海水硬骨鱼类并导致死亡,给海水鱼类养殖业造成巨大经济损失。由于刺激隐核虫体表寄生的特性,使其成为研究鱼类黏膜免疫机制的良好病原模型,可为高效疫苗的研发提供理论依据。本文综述了鱼类抗刺激隐核虫感染的黏膜免疫研究进展,以期为开展海水鱼类抗刺激隐核虫感染的免疫防控措施研究提供理论支撑。已有研究表明,受刺激隐核虫感染后,斜带石斑鱼皮肤黏液或其培养上清液能使幼虫发生阻动,由皮肤中的抗体分泌细胞产生的特异性IgM抗体在抗寄生虫感染中发挥重要作用;同时在刺激隐核虫感染时,多种免疫细胞如NCC细胞、中性粒细胞等在寄生虫周围聚集,趋化因子以及趋化因子受体表达量在寄生虫感染部位上调,暗示其调节的免疫细胞也参与抗虫免疫;此外,研究发现黄斑蓝子鱼对刺激隐核虫具有天然抗性,其血清和皮肤黏液对刺激隐核虫幼虫和滋养体均具有杀灭作用,已从其血清中分离到一种天然抗虫蛋白—L-氨基酸氧化酶,为刺激隐核虫病的防控提供新的途径;在理论研究的基础上,通过免疫实验证实疫苗防控刺激隐核虫病是可行的。     

Use of salt to control ichthyophthiriosis and prevent saprolegniosis in silver perch, Bidyanus bidyanus

The ciliate protozoan, Ichthyophthirius multifiliis , and the fungus, Saprolegnia parasitica , cause the diseases ichthyophthiriosis and saprolegniosis respectively. Both diseases are difficult to control and can cause high mortalities of freshwater fish, including the Australian silver perch, Bidyanus bidyanus (Mitchell). The efficacy of salt (NaCl) in controlling and preventing these diseases in silver perch was evaluated in aquaria and tanks. Low pH levels were also evaluated as a control for ichthyophthiriosis. Concentrations of 2 or 3 g L⁻¹ salt controlled infestations of I. multifiliis , and fish were free of both theronts and trophonts by day 8 at temperatures of 17.3–21.3 °C and by day 6 at 19.2–23.5 °C. Fish treated with 1 g L⁻¹ salt remained infested and all fish in a control treatment (0 g L⁻¹ salt) died. Although the mean survival rates of infested fish at pH levels of 5 or 6 were only 13.9% and 7.6%, respectively, there were no theronts or trophonts on surviving fish after 12 days. Silver perch harvested from a pond and treated with 2 or 3 g L⁻¹ salt did not become infected with S. parasitica and survival was 100%, whereas 16.6% of untreated (0 g L⁻¹ salt) fish became infected and survival was only 66.7%. A concentration of 2 g L⁻¹ NaCl is recommended for the control of ichthyophthiriosis and the prevention of saprolegniosis in silver perch held in tanks, aquaria and re-circulating aquaculture systems.     

Immunosuppression in juvenile carp, Cyprinus carpio L.: the effects of the corticosteroids triamcinolone acetonide and hydrocortisone 21-hemisuccinate (cortisol) on acquired immunity and the humoral antibody response to Ichthyophthirius multifiliis Fouquet

Abstract. Juvenile carp, Cyprinus carpio L., were immunized against Ichthyophthirius multifiliis following controlled exposure to the infective theront stage. On challenge, with a potentially lethal dose of theronts, all immunized fish survived, in contrast to 100% mortality in non-immunized fish. Fourteen days following exposure to the challenge infection, immune and non-immune fish were injected intraperitoneally with either triamcinolone acetonide or hydrocortisone 21-hemisuccinate (cortisol) at doses of 100 μg or 10 μg/g body weight. Controls, including immunized and non-immunized fish, were injected with saline or left untreated. Six days following corticosteroid administration, fish were exposed to challenge infections of I multifiliis. All fish treated with corticosteroid developed heavy infections with up to 100% mortality. Repeat experiments gave comparable results. Serum antibody levels recorded in similarly treated fish at intervals of 12 h and/or 1 week following corticosteroid administration were found to be relatively unaffected. The results are discussed in relation to the immune response to I multifiliis .     

肉桂活性成分肉桂醛杀灭离体多子小瓜虫效果

研究从肉桂中分离纯化出具有抑杀多子小瓜虫活性的化合物。以乙醇为提取剂,用索氏超声提取法从肉桂中提取浸膏,再用石油醚、乙酸乙酯、甲醇为萃取剂,萃取不同有效组分,以不同浓度分别进行杀灭离体多子小瓜虫实验,发现石油醚萃取物的杀虫效果最优。然后对石油醚萃取物采用硅胶层析柱和制备型高效液相色谱进行分离纯化,利用质谱和核磁波谱分析,最终鉴定其杀虫活性成分为肉桂醛;将肉桂醛溶于二甲基亚砜并用二倍梯度稀释法配成不同浓度的药液测试其对离体小瓜虫的杀灭活性。结果表明,100%杀灭滋养体和感染性幼虫的剂量分别为50和8 mg/L,半数有效浓度分别为13.9和1.8 mg/L;使用剂量在50 mg/L可完全抑制小瓜虫包囊孵化。     

槟榔、川楝子复方中草药对大黄鱼4种酶活性的影响及对刺激隐核虫的杀灭效果分析

海水小瓜虫病是养殖大黄鱼(Larimichthys crocea)和数十种海水鱼类较难控制的主要疾病,它是由刺激隐核虫(Cryptography irritans)感染引发,严重威胁鱼类养殖产业的健康发展。本研究利用复方中草药"HD-2"(槟榔、川楝子、绵马贯众、大青叶、穿心莲等以一定比例混合,超微粉碎经过200目过筛后收集粉末)投喂大黄鱼,研究大黄鱼溶菌酶(LZM)、总超氧化物歧化酶(T-SOD)、碱性磷酸酶(AKP)、酸性磷酸酶(ACP)等非特异性免疫指标变化和不同用药方式对刺激隐核虫的杀灭效果。结果显示,口服"HD-2"可以促进鱼体LZM、T-SOD、AKP、ACP活性升高,以添加2%中草药组在提高4种酶活性方面作用显著,投喂后第14~21天酶活性最高。"HD-2"对体外刺激隐核虫幼虫的杀灭实验证实:4 h内在50 mg/L浓度下对幼虫没有杀伤作用,80 mg/L、100 mg/L、200 mg/L浓度分别可以杀死20%、54%、89%的幼虫,400 mg/L浓度下幼虫被全部杀死,幼虫4 h半致死浓度为109 mg/L。在室内为期15 d的大黄鱼小瓜虫病治疗实验中,A组按20 g/kg添加"HD-2"药物口服,同时按100 mg/L浓度药浴,存活率为50%;B组按20 g/kg添加药物口服,同时按50 mg/L浓度药浴,存活率50.67%;C组,在无药浴情况下,仅按20 g/kg添加药物口服,存活率为42.67%;A、B、C组存活率均显著高于对照组存活率2.67%(P0.05)。此外,A、B、C 3组中,大黄鱼胸鳍上白点数量明显少于对照组;同时,3个组的大黄鱼鳃丝上隐核虫数量均呈显著下降趋势(P0.05),实验结束时几乎观察不到虫体;而对照组大黄鱼鳃丝上隐核虫数量明显上升。实验过程中A、B、C 3组大黄鱼释放到体外的包囊数量明显下降,第12天时其包囊数量分别下降100%、91.1%、77.7%,与对照组差异极显著(P0.01)。综上所述,口服和药浴同时用药具有最佳效果,仅口服中草药亦能达到良好治疗效果。从实用性和成本考虑,建议仅进行口服处理,即能保障大黄鱼较高成活率,中草药添加量为2%,投喂时间为6~14 d。该结果为防控鱼类小瓜虫病提供了理论参考和技术支撑,在养殖生产中将具有良好的应用前景。     

Two in vitro methods for screening potential parasiticides against Ichthyophthirius multifiliis using Tetrahymena thermophila

Ichthyophthirius multifiliis (Ich) is a ciliate parasite that infects many species of freshwater fishes worldwide and causes heavy economic losses in aquaculture. Currently, parasiticides for controlling this parasite are limited, and few pond‐practical chemical therapies exist. Hence, the search for new parasiticides is urgently needed. One challenge confronting the screening of potential parasiticides is the difficulty in raising enough parasite for efficacy testing as Ich is an obligate parasite. This study used species of Tetrahymena, Ich‐related and cultivable ciliate protozoa, to evaluate two in vitro methods to test parasiticides. Plate counting and MTS assays (CellTiter 96^® AQ_ueous Non‐Radioactive Cell Proliferation Assay) were used to compare lethal concentrations or median lethal concentrations (LC₅₀) of copper sulphate, formalin and malachite green between T. thermophila and Ich theronts or between T. thermophila and Ich tomonts. The parasiticides that killed T. thermophila have been demonstrated to kill theronts or tomonts. These in vitro methods using T. thermophila can be used to screen novel parasiticides against Ich.     

20种中草药杀灭离体小瓜虫的药效研究

选用20种不同中草药,研究其不同浓度的水提物对多子小瓜虫(Ichthyophthirius multifiliis)成虫、包囊和幼虫的离体杀灭实验效果。结果显示:0.1 g/L槟榔和乌梅对各个阶段的虫体均有杀灭效果,0.1 g/L大黄和黄芩1 h内对幼虫有杀灭效果,1.0 g/L浓度能杀灭成虫和包囊,表明槟榔、乌梅、大黄、黄芩的杀虫效果相对较好;贯众、乌药、枳壳等13种中药浓度达到10 g/L、50 g/L或100 g/L才具有一定杀虫作用,但效果不很显著;熟地黄、茯苓和黄芪即使浓度达到100 g/L时,也不能杀灭虫体。     

Effects of Water pH and Hardness on Infection of Silver Catfish,Rhamdia quelen,Fingerlings by Ichthyophthirius multifiliis

The aim of this study is to determine the effect of (1) different pH levels (5, 6, 7, 8, and 9) with water hardness 20 mg/L CaCO₃ and (2) pH 5 and 7 with varying water hardnesses (20, 60, and 120 mg/L CaCO₃) on the intensity of infection by Ichthyophthirius multifiliis in fingerlings of the silver catfish, Rhamdia quelen. In Experiment 1, the lowest and highest mortality rates were observed in fingerlings exposed to pH 5 and 9, respectively; in Experiment 2, fish kept at pH 5 and 7 with hardness 20 mg/L CaCO₃ showed significantly lowest and highest cumulative mortality, respectively, than those maintained in other conditions. The lowest intensity of trophonts/fingerling was observed at pH 5 and hardness 20 mg/L CaCO₃ in both experiments. We conclude that infection by I. multifiliis is less severe in silver catfish maintained at pH 5 and hardness 20 mg/L CaCO₃. High water hardness led to an increased intensity of trophonts and decreased survival in silver catfish kept at pH 5, but decreased intensity of trophonts and improved survival when the fish were kept at pH 7.     

Use of formalin and copper to control ichthyophthiriosis in the Australian freshwater fish silver perch (Bidyanus bidyanus Mitchell)

Infestations of the protozoan parasite, Ichthyophthirius multifiliis, cause the serious disease ichthyophthiriosis in freshwater fish throughout the world. Formalin is a recommended treatment for ichthyophthiriosis in the Australian fish silver perch (Bidyanus bidyanus Mitchell), but the disease is difficult to control in ponds, particularly at low water temperatures. Experiments were carried out to develop an improved treatment regime for formalin and to evaluate copper as a therapeutant. Silver perch fingerlings infested with I. multifiliis were stocked into 55 L aquaria at temperatures of 14.8–17.6 °C and alkalinities of 70–110 mg L^?1. Formalin (34–38% formaldehyde) or copper (24.5% copper sulphate) were added to the aquaria and then monitored and readjusted to nominal concentrations daily. A concentration of 30 mg L^?1 formalin controlled ichthyophthiriosis, but fish treated with 20 mg L^?1 remained infested with theronts and trophonts on day 17; survival at both concentrations was 100%. A concentration of 10 mg L^?1 formalin did not control ichthyophthiriosis and all fish were dead from the infestation by day 17. Fish treated with 0.1 or 0.2 mg L^?1 copper were free of theronts and trophonts by days 17 and 14, respectively, and survival was 100%. Survival at 0.05 mg L^?1 copper was 100%, but fish remained infested. At 0.25 mg L^?1 copper, survival was 82.5% and there were no theronts or trophonts on gill and skin tissues of fingerlings by day 14. There was total mortality of fish treated with 0.5 or 1.0 mg L^?1 copper suggesting these concentrations are toxic to silver perch. All fish in infested‐control treatments died. In earthen ponds containing silver perch, 0.2 mg L^?1 copper was depleted to below 0.1 mg L^?1 within 24 h, and concentrations of 25–38 mg L^?1 formalin were depleted to below 15 mg L^?1 within 48 h. Treatment regimes involving daily applications of formalin or copper controlled ichthyophthiriosis in silver perch in earthen ponds at costs of $US466.37 and $US65.58 hectare^?1 day^?1 respectively. This study has developed a new formalin‐treatment regime for the control of ichthyophthiriosis, and demonstrated that copper sulphate is a potential therapeutant for this serious disease of silver perch.