Toxicity of Four Chemotherapeutic Agents to Rabbitfish Siganus rivulatus

As aquaculture evolves from extensive pond culture to intensive tank and cage systems, chemical dips and baths are increasingly being used to treat a concomitant increase in ectoparasitic and bacterial infestations. Some of the main disease‐causing agents are ectoparasites on the skin and gills of fish. Consequently, application of chemotherapeutics is increasing in aquaculture industries in order to control outbreaks of parasitic infestations. However, the toxic effect of commonly used chemotherapeutic agents on specific aquacultured fish species is often unknown. The present work was performed to test the effect of four commonly used chemical treatments on rabbitfish, Siganus rivulatus. The lethal concentrations for 50% of population (LC₅₀) of formalin, copper sulfate, potassium permanganate, and hydrogen peroxide for S. rivulatus juveniles treated for 1 h were assessed. Formalin and potassium permanganate tolerance values were determined by calculating 72‐h LC₅₀ values through probit analysis. The 72‐h LC₅₀ values for the formalin toxicity tests were 551.0 and 1.68 mg/L, respectively. LC₅₀ of copper sulfate and hydrogen peroxide could not be determined from the concentrations tested but were found to be >3 and >700 mg/L, respectively. Accordingly, treatment concentrations of formalin and potassium permanganate used for other fish species could be lethal to S. rivulatus, but the species appears to be quite tolerant to copper sulfate and hydrogen peroxide.     

Acute Toxicity of Copper to Juvenile Freshwater Prawns,Macrobrachium rosenbergii

Abstract

Copper sulfate is an algicide that is commonly used for phytoplankton and filamentous algae control and has been used as a therapeutant in aquaculture. The objectives of this study were to determine the acute toxicity of copper sulfate and the safe level for use in freshwater prawn, Macrobrachium rosenbergii, production ponds in a high calcium and alkalinity environment. Six concentrations of copper sulfate (0, 0.2, 0.4, 0.6, 0.8, 1.0 mg/L) were tested in 8-L glass aquaria for 48 hours with three replicate aquaria per treatment. Concentrations of calcium hardness and alkalinity were set at 100 mg/L using calcium chloride and sodium bicarbonate, respectively. After 48 hours, survival of the control treatment (0% CuSO₄) averaged 97%, which was significantly higher (P< 0.05) than that of all other treatments. The survival in the 0.2 mg/L and 0.4 mg/L (70% and 73%, respectively) concentrations of CuSO₄ were significantly greater (P< 0.05) than higher dose treatments; but were not significantly different from each other (P> 0.05). Treatments containing 0.6, 0.8, and 1.0-mg/L copper sulfate demonstrated a dramatic decrease in prawn survival, which averaged 30, 7, and 0%, respectively. Regression analysis of the data predicted 48-hour LC₅₀ for copper sulfate tobe0.46 mg/L. Since recommended application rates for use of copper sulfate as an algicide are 1.0 mg/L or more for water with alkalinities of 100 mg/L, copper sulfate treatments are not recommended for prawn production ponds.     

Chemical Prevention and Treatment of Winter Saprolegniosis (“Winter Kill”) in Channel Catfish Ictalurus puncfatus1

The efficacies of formalin, potassium permanganate, sodium chloride, and copper sulfate as prophylactic treatments for saprolegniosis (“winter kill”) in channel caffish Icralums puncratus were evaluated. Formalin and copper sulfate were also evaluated as postinfective treatments for the disease. Each of the five experiments was conducted with 5–to 7-g channel catfish placed in static water aquaria maintained in refrigerated tanks. Water temperature was reduced from 25 to 10 C within 36 h and maintained at 10 ± 0.5 C for 28 d. Fish were exposed to cultured Saprolegnia sp. at 20 C, and morbidity and mortality data were recorded for 28 d. Saprolegnia sp.-associated mortalities occurred 7–10 d after exposure. Formalin (25 mg/L) was effective as both a prophylactic and postinfective treatment for saprolegniosis. Copper sulfate was effective in preventing saprolegniosis at a concentration of 0.1 mg/L, but was ineffective as a postinfective treatment. Sodium chloride at 5,000 mg/L was effective in preventing saprolegniosis, but was not practical for use in the commercial catfish industry. Potassium permanganate (up to 0.5 mg/L) was not effective in preventing or treating saprolegniosis in channel caffish. Based on the results of this study, it may be possible to prevent saprolegniosis in channel catfish using formalin or copper sulfate during winter when fish are immunosuppressed by rapid decreases in water temperature or to treat infected fish with formalin. However, the routine use of chemicals to control this disease should not be recommended until studies on their efficacy under typical caffish culture conditions and the effect of long-term use of chemicals on fish and on the environment are completed.     

Saprolegnia diclina IIIA and S. parasitica employ different infection strategies when colonizing eggs of Atlantic salmon,Salmo salar L.

Here, we address the morphological changes of eyed eggs of Atlantic salmon, Salmo salar L. infected with Saprolegnia from a commercial hatchery and after experimental infection. Eyed eggs infected with Saprolegnia spp. from 10 Atlantic salmon females were obtained. Egg pathology was investigated by light and scanning electron microscopy. Eggs from six of ten females were infected with S. parasitica, and two females had infections with S. diclina clade IIIA; two Saprolegnia isolates remained unidentified. Light microscopy showed S. diclina infection resulted in the chorion in some areas being completely destroyed, whereas eggs infected with S. parasitica had an apparently intact chorion with hyphae growing within or beneath the chorion. The same contrasting pathology was found in experimentally infected eggs. Scanning electron microscopy revealed that S. parasitica grew on the egg surface and hyphae were found penetrating the chorion of the egg, and re‐emerging on the surface away from the infection site. The two Saprolegnia species employ different infection strategies when colonizing salmon eggs. Saprolegnia diclina infection results in chorion destruction, while S. parasitica penetrates intact chorion. We discuss the possibility these infection mechanisms representing a necrotrophic (S. diclina) vs. a facultative biotrophic strategy (S. parasitica).     

Slow‐release Coated Copper Sulfate as an Algicide for Aquaculture

A coated copper sulfate algicide designed for controlled release of copper was evaluated for its effectiveness in controlling phytoplankton in hybrid catfish, ♀Ictalurus punctatus × ♂Ictalurus furcatus, ponds. Copper concentrations were greater in ponds receiving weekly treatments with copper sulfate crystals than in ponds in which the coated copper sulfate was suspended in porous bags and left in ponds during the study. However, the coated copper sulfate treatment provided a similar degree of phytoplankton control for a period of about 4 mo. Copper additions did not negatively affect catfish survival, production, or feed conversion in either the copper sulfate crystal treatment or in the coated copper sulfate treatment as compared with the control (P > 0.05). Flavor scores for fish did not differ between control and treatments (P > 0.05). The coated copper sulfate appeared to be a potentially effective method for controlling phytoplankton in aquaculture ponds. It would be easier to apply and require fewer applications, and the coated copper algicide would not present a fish toxicity issue that can arise from high copper concentration immediately following copper sulfate crystal treatment.     

Antifungal Activity of Rhein and Aloe‐Emodin from Rheum palmatum on Fish Pathogenic Saprolegnia sp.

Saprolegnia infections cause severe economic losses among freshwater fish farming. In this study, two known compounds, rhein and aloe‐emodin, were isolated from Rheum palmatum, and the in vitro inhibitory activity of both compounds against mycelial growth and spore germination of Saprolegnia was tested. Both rhein and aloe‐emodin were able to decrease Saprolegnia mycelial growth and spore activity in all tested concentrations after exposure for 48 h. Complete inhibition of mycelial growth was observed at 20 mg/L for rhein and at 50 mg/L for aloe‐emodin, while spore germination was 100% prevented at 16 and 40 mg/L for rhein and aloe‐emodin, respectively. Because rhein showed stronger in vitro anti‐Saprolegnia activity, it was further tested in vivo to measure the prevention and treatment efficacy on Saprolegnia infection of grass carp. Its acute activity to grass carp was also evaluated. The results revealed that exposure to rhein at 20 mg/L for 7 d could prevent 93.3% of infections by Saprolegnia in abraded grass carp, while 67.7% of infected fish could be recovered by treatment with rhein. The 48‐h median lethal concentration (48 h‐LC₅₀) to grass carp was 148.5 mg/L, which is about 7.4 times the effective dose indicating the safety for the use of rhein. This study suggests that rhein has promising anti‐Saprolegnia activity and may be an option in preventing and controlling Saprolegnia infection.     

In vitro activity of chemicals and commercial products against Saprolegnia parasitica and Saprolegnia delica strains

Oomycetes of the genus Saprolegnia are responsible for severe economic losses in freshwater aquaculture. Following the ban of malachite green in food fish production, the demand for new treatments pushes towards the selection of more safe and environment‐friendly products. In the present work, in vitro activity of ten chemicals and three commercial products was tested on different strains of Saprolegnia, using malachite green as reference compound. The compounds were screened in agar and in water to assess the minimum inhibitory concentration (MIC) and the minimum lethal concentration (MLC), respectively. Two strains of Saprolegnia parasitica and one isolate of Saprolegnia delica were tested in triplicate per each concentration. Among tested chemicals, benzoic acid showed the lowest MIC (100 ppm) followed by acetic acid, iodoacetic acid and copper sulphate (250 ppm). Sodium percarbonate was not effective at any tested concentration. Among commercial products, Virkon^?S was effective in inhibiting the growth of the mycelium (MIC = MLC = 1,000 ppm). Actidrox® and Detarox® AP showed MIC = 5,000 and 1,000 ppm, respectively, while MLCs were 10‐fold lower than MICs, possibly due to a higher activity of these products in water. Similarly, a higher effectiveness in water was observed also for iodoacetic acid.     

In Vitro Screening of Fungicidal Chemicals for Antifungal Activity against Saprolegnia

Saprolegnia is an important fish fungal pathogen that often results in significant economic losses to freshwater aquaculture. To find effective drugs to control saprolegniasis, 30 fungicidal chemicals used in agriculture were screened, in which kresoxim‐methyl and azoxystrobin, with minimum inhibitory concentration (MIC) values of 1.0 and 0.5 mg/L, respectively, showed good in vitro antifungal activities against Saprolegnia. Azoxystrobin has the most promising anti‐Saprolegnia activity with 50% effective concentration (EC₅₀) value of 0.212 mg/L against mycelial growth and minimum fungicidal concentration (MFC) value of 0.13 mg/L against spores, while EC₅₀ and MFC values to kresoxim‐methyl are 0.240 and 0.25 mg/L, respectively. Through the acute toxicity assay using goldfish, Carassius auratus, azoxystrobin exhibited wider margin of safety with a safe concentration (SC) value of 0.553 mg/L than kresoxim‐methyl with an SC value of 0.131 mg/L. These findings demonstrated that azoxystrobin has the potential for the development of therapy for the control of Saprolegnia in aquaculture. Both kresoxim‐methyl and azoxystrobin were tested with a post‐antifungal effects (PAFE) assay and the results revealed that the two chemicals had no significant effect on fungal growth inhibition after a 1‐hour exposure, indicating that the treatment needs to be carried out over an extended period.     

Reduction of in vitro growth in Flavobacterium columnare and Saprolegnia parasitica by products containing peracetic acid

Commercial products containing peracetic acid (PAA) are strong disinfectants with a wide spectrum of antimicrobial activity and have been suggested as potential therapeutic agents in aquaculture. The aim of this study was to compare the in vitro reduction of growth on two fish pathogens, Flavobacterium columnare and Saprolegnia parasitica, by seven commercial PAA‐containing products. Flavobacterium columnare was exposed to 1, 2, 4, 6, 8 and 10 mg L^?1 PAA and S. parasitica was exposed to 0.5, 1, 2, 4, 6, 8 and 10 mg L^?1 PAA in petri dishes for 24 h incubation. The reduction of growth was measured in comparison to a PAA‐free control. A reduction of the growth was observed for both pathogens with increasing PAA concentration. Hydrogen peroxide (H₂O₂) possibly has a role in the effectiveness of the products, since products with lower PAA concentrations had a higher concentration of H₂O₂. The commercial products with a low concentration of PAA and a low PAA:H₂O₂‐ratio were generally more effective against pathogens. The practical application of the products with low PAA concentration should be prioritized.     

巨须裂腹鱼水霉菌的分离鉴定及其对脾脏转录组的影响

为分析感染水霉菌对巨须裂腹鱼脾脏转录组的影响，探索水霉菌感染巨须裂腹鱼的分子机制，实验随机选取生活在同一水域中的5尾健康和5尾感染水霉菌的巨须裂腹鱼，采用PDA琼脂培养基和分子生物学方法对巨须裂腹鱼水霉菌进行分离鉴定，并采用Illumina HiSeqTM 2000 高通量测序平台，对健康和感染水霉菌的巨须裂腹鱼脾脏组织进行转录组测序，并对测序数据进行拼接、注释和差异表达基因分析。结果显示，从巨须裂腹鱼皮肤上分离鉴定得到3株水霉菌；转录组数据显示，健康组和感染水霉病组分别获得46 619 504 条和43 912 876 条数据，与健康组相比，感染水霉菌组共有1 889 个基因发生差异表达，其中1 414 个基因上调，475 个基因下调，随机选取6个差异表达基因进行实时荧光定量PCR (RT-qPCR)验证，验证结果与转录组测序一致。对健康组和感染水霉菌组的差异表达基因进行GO功能富集发现，上调基因主要富集于241个功能中，下调基因主要富集于60个功能中，上述基因主要涉及分子功能类、细胞组分类和生物过程类等生理功能；KEGG通路富集分析发现，差异表达基因主要富集在免疫疾病、内分泌和代谢疾病、病毒感染性疾病、消化系统及排泄系统等。研究表明，感染水霉菌会影响巨须裂腹鱼脾脏组织多种基因的表达量，实验结果为进一步探索巨须裂腹鱼水霉菌的感染机制奠定了基础。     

In vitro Antifungal activity of essential oils from Tymbra,Origanum, Satureja species and some pure compounds on the fish pathogenic fungus,Saprolegnia parasitica

In the present study, the chemical composition and antifungal activity of the essential oils of the three Lamiaceae species, black tyme (Thymbra spicata L.), oregano (Origanum onites L.) and savory (Satureja tymbra L.) against Saprolegnia parasitica Coker strains (3) were evaluated. The composition of oils was analysed by gas chromatography/mass spectrometry (GC/MS). The major constituent of the oils was carvacrol (82.68% in Thymbra spicata, 82.24% in Origanum onites and 52.38% in Satureja tymbra). The antifungal activity of essential oils was determined by a tube dilution and disc diffusion method. All essential oils inhibited fungal strains at concentration of 100 μL mL^?1. The essential oil of O. onites and T. spicata was the most active (MIC 10 and 50 μL mL^?1, respectively). Thymol did not show inhibiting activity. The essential oils exhibited stronger inhibition than pure carvacrol. Essential oil derived from Tymbra, Origanum and Satureja species has the potential to be used as health control of rainbow trout (Oncorhyncus mykiss) against S. parasitica infection. This study describes the antifungal activity of three essential oils for developing alternative and native control methods against Saprolegniasis.     

In vitro and in vivo antifungal activity of Satureja cuneifolia ten essential oil on Saprolegnia parasitica strains isolated from rainbow trout (Oncorhynchus mykiss,Walbaum) eggs

In the present study, the chemical composition and the antifungal properties against Saprolegnia parasitica (in vitro and in vivo) of the essential oils of thyme (Satureja cuneifolia) from Mediterranean region of Turkey were evaluated for the first time. The composition of oils was analysed using gas chromatography/mass spectrometry (GC/MS). The major constituents of oil of S. cuneifolia were cavracrol (46,84%) and cymene (16.90%). Antifungal effects of S. cuneifolia essential oil against S. parasitica strains (A1 and E1) were detected by disc diffusion and tube dilution assays. The antifungal effect of S. cuneifolia was determined to be stronger against S. parasitica E1 isolate (MIC 50 μL mL^?1, MLC 250 μL mL^?1) compared with S. parasitica A1 isolate (MIC 50 μL mL^?1, MLC 500 μL mL^?1). Following in vitro assays, effective doses of S. cuneifolia for disease control in rainbow trout eggs experimentally infected with S. parasitica were investigated. For this aim, infected eggs were treated with the essential oil (0, 5, 10, 20 and 50 ppm) during incubation period (21 days) after fertilization. Formalin (5 mL L^?1) was used as positive control. Hatching rate of eggs at the end of incubation period were calculated. The highest hatching rates were recorded in S. parasitica E1 strain at 5 and 10 ppm concentrations of S. cuneifolia and in S. parasitica A1 strain at 10 and 20 ppm (P < 0.05).     

Levels of Vitellogenin in Male Japanese Medaka (Oryzias latipes) Exposed to the Chemotherapeutics: Oxytetracycline,Romet-30®, and Copper Sulfate

ABSTRACT

Japanese medaka (Oryzias latipes) were exposed to oxytetracycline and Romet-30^® at daily doses via feed of 0.06 mg, 0.11 mg, and 0.28 mg per gram body weight for 11 days, and at daily doses of 0.05 mg, 0.10 mg, and 0.15 mg per gram body weight for 5 days, respectively. In addition, fish were exposed to copper sulfate in their aquaria water at 1.85 mg/L for 1 h each day (over a span of 1 day, 7 consecutive days, or 1 day in every 3 to 5 days for a total of seven doses). Vitellogenin levels were measured in fish using a sandwich enzyme-linked immunosorbent assay (ELISA). Vitellogenin levels were not induced from exposure to either oxytetracycline or Romet-30® (P > 0.05); however, copper sulfate for 1 h on 1 day showed a decrease in vitellogenin from the control fish and other treatment groups (P = 0.007). Under these test conditions, oxytetracycline, Romet-30, and copper sulfate were not found to act in medaka as estrogenic compounds by inducing vitellogenin.     

Anesthetic Efficacy of Clove Oil,Propofol, 2‐Phenoxyethanol,and Ketamine Hydrochloride on Persian Sturgeon,Acipenser persicus,Juveniles

Anesthetics are commonly used in the aquaculture industry to reduce stress and prevent mortality of fish during transportation, handling, and surgical procedures. This study assessed the efficacy of four anesthetic agents (clove oil, propofol, 2‐phenoxyethanol [2‐PE], and ketamine hydrochloride) on Persian sturgeon, Acipenser persicus, juveniles. In addition, results of the first experiment were used to evaluate sedation concentrations suitable for transportation of Persian sturgeon. The concentrations of anesthetics or sedatives evaluated in the first experiment were: 25, 50, 75, and 100 mg/L for clove oil; 1, 1.25, 2.5, and 5 mg/L for propofol; 110, 330, 550, and 770 mg/L for 2‐PE; and 1250, 2500, 3750, and 5000 mg/L for ketamine hydrochloride. Results show significant reduction in time to anesthesia and significant increase in recovery time with increase in concentration of all anesthetics. The most clinically useful concentrations of anesthetics tested were between 25 and 50 mg/L for clove oil, less than 1 mg/L for propofol, 330 mg/L for 2‐PE, and none of the tested concentrations for ketamine hydrochloride. In the second experiment, juveniles were placed in low concentrations of anesthetic solutions for 24 h and survival assessed. The four anesthetics tested are suitable for light sedation during transportation of A. persicus juveniles. Results are helpful to scientists working with Persian sturgeon aquaculture and restocking programs.     

Toxicity of Peracetic Acid to Fish: Variation among Species and Impact of Water Chemistry

There has been strong interest in the use of peracetic acid (PAA) in aquaculture as it can be used to disinfect water and hard surfaces and thereby eliminate or lower the burden of fish pathogens. Unfortunately, there has been little research on the toxicity of PAA to fish. Twelve species of fingerling fish that are important to aquaculture were exposed to PAA for 24 h in static toxicity bioassays in well water. These fish were: fathead minnow, Pimephales promelas; black‐nose crappie, Pomoxis nigromaculatus; bluegill, Lepomis macrochirus; blue tilapia, Oreochromis aureus; channel catfish, Ictalurus punctatus; golden shiner, Notemigonus crysoleucas; goldfish, Carassius auratus; grass carp, Ctenopharyngodon idella; largemouth bass, Micropterus salmoides; rainbow trout, Oncorhynchus mykiss; sunshine bass, Morone chrysops × M. saxatilis; and walleye, Sander vitreus. Median lethal concentration (LC₅₀) values were estimated with the trimmed Spearman–Karber method using nominal PAA concentrations. The mean 24‐h LC₅₀ values ranged from 2.8 to 9.3 mg/L PAA. Fathead minnow were very sensitive and blue tilapia were very tolerant to PAA exposure; LC₅₀ values of other species tested were within the range of 4.1–6.2 mg/L PAA. More importantly, the 24‐h no‐observed‐effect concentration (NOEC) ranged from 1.9 to 5.8 mg/L PAA; the NOEC would be considered as the safe range for culturists to investigate the use of PAA. Decreased alkalinity/hardness increased the toxicity of PAA, while a small increase of dissolved organic content had no effect on PAA toxicity. Results of the present study are important information on the safe application of PAA for the aquaculture industry.     

Chemical composition and in vitro antifungal activity of Sambucus ebulus and Actinidia deliciosa on the fish pathogenic fungus,Saprolegnia parasitica

The aim of the present study was to determine the chemical composition of Sambucus ebulus and Actinidia deliciosa ethanolic extracts as well as their in vitro antifungal activity on the mycelial growth of the water mold, Saprolegnia parasitica. The preliminary minimum inhibition concentration (MIC) and minimum lethal concentration (MLC) were determined by the HeMP method and finally, concentrations of each extract ranging from 1 to 10% were prepared by an agar dilution method to assess the in vitro antifungal activity, quantitatively. Both herbal extracts inhibited growth of Saprolegnia hyphae in vitro. Complete in vitro growth inhibition was found at a concentration of ≥5% for S. ebulus, whereas it was not observed even at 10% concentration of A. deliciosa. Based on gas chromatography coupled with mass spectrometry (GC/MS) analysis, the main constituents of S. ebulus include monophthalate (66.17%), fatty acids (26.47%), phytol (4.25%), and acetic acid (2.11%). Using colorimetric assays, A. deliciosa contained phenolic contents at 162 mg gallic acid (GAE)/g DW and flavonoid contents at 2.31 mg quercetin (QE)/g DW. In conclusion, the results of this study indicated that S. ebulus and A. deliciosa showed some antifungal activities against S. parasitica with formerly exhibiting stronger activity (p < 0.05).

     

Acute and Chronic Effects of Ammonia on Juvenile Cuttlefish,Sepia pharaonis

The aim of this study was to provide a reference value for the safe regulation and control of ammonia nitrogen in the aquaculture of Sepia pharaonis. The effects of acute and chronic toxicity of ammonia on the cuttlefish, S. pharaonis, were tested experimentally using juvenile S. pharaonis. The results showed that the half‐lethal concentration (LC₅₀ ) values of ammonia nitrogen in juvenile S. pharaonis with a body weight of 6.52 ± 0. 23 g at 24, 48, 72, and 96 h were 31.72, 25.77, 23.33, and 18.33 mg/L, respectively, and the corresponding un‐ionized ammonia nitrogen (UIA‐N) concentrations were 1.66, 1.35, 1.22, and 0.96 mg/L, respectively. Compared with the control, the survival rate, specific growth rate, and feed intake of juvenile S. pharaonis declined significantly, and the feed conversion ratio and hepatosomatic index increased significantly at 56 d after exposure to >1 mg/L ammonia nitrogen. Juvenile S. pharaonis should be maintained at a concentration of ammonia nitrogen of no more than 1 mg/L (UIA‐N is 0.056 mg/L) in culture, and removing harmful nitrogenous wastes from the seawater is critical in maintaining cuttlefish culture.     

Use of Onion (Allium cepa) and Garlic (Allium sativum) Wastes for the Prevention of Fungal Disease (Saprolegnia parasitica) on Eggs of Rainbow Trout (Oncorhynchus mykiss)

This study was designed to prevent fungal disease (Saprolegnia parasitica) that occurs on rainbow trout eggs (Oncorhynchus mykiss) by using wastes of onion (Allium cepa) and garlic (Allium sativum) plants. For this purpose, fertilized rainbow trout eggs were exposed to garlic skin, garlic stem and onion skin aqueous methanolic extracts by bathing in concentrations of 0.4, 0.8, 1.6 and 3.2 g/L, whereas the control group was left untreated. The larvae in all groups were monitored until they become free-swimming larvae, the number of eggs died due to fungus was recorded, and the data obtained from experimental groups and control group were compared. As a result, it was determined that onion skin had no effect on the number of eggs that died due to fungus (p > .05), while garlic skin and garlic stem extracts significantly reduced the number of fungal infestations without affecting the number of live larvae or the embryological development of the eggs (p < .05). In light of these data, we conclude that garlic skin (0.4, 0.8, and 1.6 g/L) and garlic stem (0.8 and 1.6 g/L) aqueous methanolic extracts are effective at preventing Saprolegnia parasitica infestation on rainbow trout eggs and may be used in aquaculture.     

Protective effects of a synbiotic against experimental Saprolegnia parasitica infection in rainbow trout (Oncorhynchus mykiss)

A combination of probiotics and prebiotics as synbiotics allows assessing their synergistic effects. This study evaluated the effects of a synbiotic supplement on growth performance, haematological parameters and resistance to Saprolegnia parasitica in rainbow trout, Oncorhynchus mykiss (Walbaum) fingerlings. Fish fed a dietary synbiotic in three levels of 0.5, 1.0 and 1.5 g kg^?1 thrice a day. The fingerlings were challenged with Saprolegnia parasitica after 60 days post feeding and their mortalities recorded up to 15 days. The fingerlings at all three experimental treatments showed significant (P < 0.05) increases in final mean weights and specific growth rates (SGR). The best feed conversion ratio (FCR), feed conversion efficiency (FCE) and maximum survival rate were also obtained by the fish fed 1.0 g synbiotic kg^?1 diet. Furthermore, supplementation with synbiotic significantly increased blood factors at all treatments. After challenges with Saprolegnia parasitica, the synbiotic‐fed groups showed significantly higher survival rates compared with the control group. These results reveal that a dietary synbiotic of 1.0 g kg^?1 fed for 60 days leads to increased growth performance and survival rate as well as improved feeding efficiency in rainbow trout fingerling, rendering them more resistant against infection by Saprolegnia parasitica.     

Impact of Copper Sulfate on Plankton in Channel Catfish Nursery Ponds

Many fish culturists are interested in applying copper sulfate pentahydrate (CSP) to channel catfish, Ictalurus punctatus, nursery ponds as a prophylactic treatment for trematode infection and proliferative gill disease by killing snails and Dero sp., respectively, before stocking fry. However, copper is an algaecide and may adversely affect phytoplankton and zooplankton populations. We evaluated the effects of prophylactic use of copper sulfate in catfish nursery ponds on water quality and phytoplankton and zooplankton populations. In 2006, treatments of 0 mg/L CSP, 3 mg/L CSP (0.77 mg/L Cu), and 6 mg/L CSP (1.54 mg/L Cu) were randomly assigned to 0.04‐ha ponds. In 2007, only treatments of 0 and 3 mg/L CSP were randomly assigned to the 16 ponds. Ponds treated with CSP had significantly higher pH and significantly lower total ammonia concentrations. Treatment of both CSP rates increased total algal concentrations but reduced desirable zooplankton groups for catfish culture. CSP has been shown to be effective in reducing snail populations at the rate used in this study. CSP treatment also appears to be beneficial to the algal bloom, shifting the algal population to green algae and increasing total algal biomass within 1 wk after CSP treatment. Although zooplankton populations were adversely affected, populations of important zooplankton to catfish fry began rebounding 6–12 d after CSP treatment. Therefore, if CSP is used to treat catfish fry ponds of similar water composition used in this study, fry should not be stocked for about 2 wk after CSP application to allow time for the desirable zooplankton densities to begin increasing.