Quality Changes in Gamma Irradiated Marinades of Anchovy (Engraulis anchoita) During Refrigerated Storage

The effect of gamma irradiation (0, 1.8, and 3.3 kGy) on the microbiological, chemical, and color characteristics of marinated (7% acetic acid and 10% NaCl) and vacuum-packed anchovy fillets was analyzed during 20 months of refrigerated storage (4 ± 1°C). Acidity, pH, water activity (a_w), total volatile basic nitrogen (TVBN), lipid oxidation, and color parameters were determined. Mesophilic and psychrotrophic bacteria, sulphite-reducing clostridia, total and fecal coliforms, Staphylococcus spp., yeasts, and molds were investigated. Gamma irradiation reduced the initial mesophilic bacterial counts and inhibited mesophils growth during 20 months. As a result, the production of TVBN during storage was lower in irradiated samples than in control. Also, lipid oxidation was lower in irradiated samples than in nonirradiated. The color of anchovy fillets was not affected by the irradiation treatment. Even if nonirradiated anchovy fillets presented a high stability in comparison with the traditional product (in flasks with vegetable oil and spices), gamma irradiation improved the microbiological and chemical quality of anchovy fillet marinades without inducing changes on its characteristic color for 20 months.     

Control of Bacterial Pathogens by Liquid Smoke and Sodium Lactate During Processing of Cold-Smoked and Dried Salmon Strips

Abstract

Liquid smoke and sodium lactate (NaL) were evaluated as inhibitors to control microbial growth in Alaskan native-style smoked and dried salmon strips. Brined salmon strips were dipped in aqueous solutions of liquid smoke (25%, 50%, 75%, 100%) or NaL (20%, 40%) and then inoculated with 3000 CFU of Staphylococcus aureus/100 g sample prior to drying in a laboratory smoke house without application of smoke, at 30°C for 5 days. S. aureus populations increased to 10⁵/g in non-dipped control samples, 4.5 × 10³/g in 20%, and 4.6 × 10²/g in 40% NaL samples. Liquid smoke was not effective at a concentration of 25%, but reduced S. aureus levels below detectable limits when used at higher concentrations. When the additives were tested by a processor in Alaska, aerobic populations were less than 30 CFU/g with 30% NaL and 50% liquid smoke and the water activity (a_w) of these finished products was below 0.85, a level that would inhibit further microbial growth. Processors should test their products for microbiological populations, WPS and a_w until they can show that their process is adequate to control bacterial pathogens.     

Influence of Water and Glycerol Contents on the aw of Fish Pastes

Abstract

The influence of fish water content on the characteristics of water activity (a_w) of reduced paste was studied. Two fish species were used: a fat species, mackerel (Scomber japonicus marplatensis), and a lean species, Brazilian sandperch (Pseudopercis semifasciata). Glycerol (from 15 to 50%) was used to decrease a_w of the cooked fish paste.(54.12% and 77.89%) in mackerel, two relationships of a_w versus percent added glycerol were obtained, and for Brazilian sandperch one relationship was obtained.     

Preparation of Cookies with Various Native Seaweeds Found on the Korean Coast

ABSTRACT

We investigated the quality characteristics of cookies prepared using different seaweeds native to the Korean coast. Flour made from four different seaweed species (Sargassum fulvellum, Enteromorpha linza, Codium fragile, and Hizikia fusiforme) was used to replace 5% of the regular flour while preparing the cookies. The seaweeds significantly affected solvent retention capacity, thus interfering with gluten network formation. Consequently, the addition of seaweed changed several variables in the cookies, such as moisture content, spread factor, and breaking stress. In sensory evaluation, cookies with Hizikia fusiforme were the most preferred, confirming the possibility of developing cookie products using this seaweed species.     

The Influence of Seaweed Composite Flour on the Physicochemical Properties of Muffin

Seaweed has a great potential to be used as an important ingredient in food processing, as it contains a significant content of soluble polysaccharides and has a potential function as a dietary fiber. In this study, seaweed powder (Kappaphycus alvarezii) was incorporated (2–10%) with wheat flour for the production of muffins. The effect of seaweed composite flour on the quality of muffins was investigated using various techniques, such as texture profile and proximate analyses, as well as sensory evaluation. Modification of the muffin formulation to include seaweed powder improved the composition of ash, crude fiber, and moisture content, while the protein and carbohydrate levels decreased, compared to the control sample. An increase in the seaweed component reduced the muffin height, volume, and specific volume. According to the experimental texture profile analysis data, the seaweed affected the textural characteristics of the muffins, increasing the hardness and decreasing the springiness. Sensory evaluation revealed that seaweed powder could be used in the muffin formulation up to 6%, without significantly impacting the color, aroma, and taste attributes relative to the control sample. For overall acceptability, however, the panelists preferred muffins without seaweed powder.     

Impacts of Hydrocolloids on Physical,Microbiological and Sensorial Qualities of Swai-Fish-Based Emulsions Subjected to High Pressure Processing

The objective of this study was to examine how konjac flour or carboxymethylcellulose (CMC) could improve the physical, microbiological, and sensorial qualities of pressurized Swai fish-based emulsions. The properties of the pressurized batches were also compared with those of the heated emulsions. Accordingly, Swai fish-based emulsions containing mixed fermented-soybeans were stabilized by either konjac flour or CMC, 0.1–0.3%. The fish batters were then subjected to pressurization (600 MPa/25°C/20 min) or thermal treatment (72°C/30 min). The results showed that both hydrocolloids enabled improvement of the color of fish emulsions. Regarding the impact of hydrocolloids on other properties, CMC addition enhanced water holding capacity, gel strength, and elasticity more than konjac flour addition. Regarding processing effects, pressurization gave rise to products with greater water holding capacity and higher sensorial scores than the thermal treatments. However, thermal treatments increased the gel strength and elasticity of the products more than pressurization. Overall, both processes could equally inhibit bacterial cells and some spores of B. subtilis.     

Apparent digestibility of selected ingredients in diets for juvenile grouper, Epinephelus coioides (Hamilton)

Apparent digestibility coefficients (ADCs) for dry matter (ADC_dm) and crude protein (ADC_cp) of selected feed ingredients were determined in vivo for grouper using passive faeces collection (Guelph System). A reference diet (RF) and test diets (consisted of 70% RF and 30% test ingredient) with 1% Cr₂O₃ as an inert indicator were used. An RF contained 45% protein, 10% fat and 15.7 kJ g^?1 metabolizable energy. Three isonitrogenous and isocaloric diets, each contained a test ingredient (white fish meal, white cowpea meal and ipil‐ipil leaf meal), were used in a growth study based on ADC_cp of feed ingredients. An RF without Cr₂O₃ was a control. The ADC values of experimental diets were also determined. In grouper, the ADC_dm of white cowpea meal, defatted soybean meal, wheat flour and shrimp meal (74–76%) were significantly lower than that of squid meal (99%), but comparable with those of the fish meals (84–89%). No significant difference was observed between the ADC_dm of ipil‐ipil leaf meal, rice bran and wheat flour (56–73%). The ADC_cp of white cowpea meal and defatted soybean meal were similar to those of the fish meals, squid meal and shrimp meal (94–99%). The ADC_cp of wheat flour was comparable with that of ipil‐ipil leaf meal (79–83%). Rice bran had the lowest ADC_cp value of 43%. Based on specific growth rate (SGR), the growth of fish fed white cowpea meal‐based diets was similar to that of the control fish (3.2–3.3% day^?1). Also, no significant difference was observed between the ADC_dm (68–72%) and ADC_cp (88–91%) of white cowpea meal‐based diet and the control diet. The results suggest that ADC values can be used as indicators to determine the nutritional value of feed ingredients. White cowpea meal can be incorporated as a protein source in practical diet for grouper at 20.5% of the diet with no adverse effect on growth.     

Inducing synchronous ovarian maturation in the crayfish,Procambarus clarkii,via eyestalk interventional injection as compared with eyestalk ablation and combined injection of serotonin and domperidone

We examined the feasibility of inducing synchronous ovarian maturation in the crayfish, Procambarus clarkii, via eyestalk interventional injection (EI) using a Bletilla striata polysaccharide (BSP) gelatin containing tranexamic acid (TRA), domperidone (DOM) or serotonin (5‐HT). In total, 360 females were randomly assigned to seven experimental groups and a control group. The average survival rate (SR%) and average synchronous ovarian maturation rate (SMR%) in survivors in the EI groups, EI‐TRA, EI‐DOM, EI‐5HT were compared with bilateral eyestalk ablation (BEA), unilateral eyestalk ablation (UEA), abdominal injection (AI) of DOM (0.5 mg crayfish^?1) alone (AI‐DOM) or combined with 5‐HT (0.5 mg crayfish^?1) (AI‐DOM+5‐HT). The experiment covered a prolonged period of 32 days until two ovigerous females were observed in BEA. EI‐DOM achieved a SMR (66.67 ± 9.62%) higher than the control (22.05 ± 3.06%) (P < 0.05), but lower than BEA (88.89 ± 11.11%), UEA (63.33 ± 18.56) and AI‐DOM+5‐HT (59.26 ± 10.14%) (P > 0.05). EI‐DOM also achieved a higher SR (53.33 ± 3.85%) than BEA (15.56 ± 2.22), UEA (24.44 ± 5.88) (P < 0.05) and AI‐DOM+5HT (51.11 ± 4.44) (P > 0.05). However, EI‐TRA (SR = 28.89 ± 4.44, SMR = 37.78 ± 2.22) and EI‐5‐HT (SR = 15.56 ±4.44, SMR = 22.22 ± 11.11) failed to induce significantly higher SMR than the control. These findings suggest that EI methods, such as EI‐DOM, may have positive characteristics for the development of inexpensive and less labour‐intensive techniques for induction of ovarian maturation in decapods.     

Moisture Adsorption Isotherms and Thermodynamic Properties of Penaeus vannamei Meat with and without Maltodextrin Addition

ABSTRACT

Moisture adsorption isotherms of freeze-dried Penaeus vannamei meat containing maltodextrin (PV-MD) and maltodextrin-free (PV) samples were determined at temperatures of 5, 15, 25, 35, and 45°C with water activity (a_w) ranging from 0.112 to 0.931. The adsorption behaviors of PV and PV-MD followed type III isotherms. The equilibrium moisture content of PV and PV-MD decreased with increasing temperature and increased with increasing a_w. The monolayer moisture content increased with the addition of maltodextrin and was observed to be 0.0611–0.0824 and 0.0734–0.1034 g water/g dry solids for PV and PV-MD, respectively. Eight models were employed to fit experimental data, and the Guggenheim-Anderson-de Boer (GAB) model achieved the best fit. For both PV and PV-MD, the differential enthalpy and entropy and integral enthalpy decreased with increasing moisture content. The integral entropy was negative in value and increased with increasing moisture content. The spreading pressure increased with increasing a_w but decreased with increasing temperature. A plot of differential enthalpy versus entropy satisfied the enthalpy-entropy compensation theory, and the adsorption behavior of P. vannamei meat was enthalpy-driven and spontaneous. Addition of maltodextrin increased the differential enthalpy and entropy, integral enthalpy, and spreading pressure, but decreased the integral entropy of P. vannamei meat.     

Effects of Modified Atmospheric Packaging Conditions on the Quality Changes of Pasteurized Oyster (Crassostrea belcheri) Meat during Chilled Storage

ABSTRACT

The effects of different atmospheric conditions on the quality and the shelf life of pasteurized oyster meat in chilled storage were investigated. The alternatives tested for pasteurized oyster meat were normal air (Control), 75% CO₂/25% N₂ (MAP-1), 75% CO₂/25% O₂ (MAP-2), 75% CO₂/5% O₂/20% N₂ (MAP-3), and vacuum packing (VP). The various observations of microbiological (total viable count (TVC), Enterobacteriaceae, Pseudomonas spp., lactic acid bacteria (LAB), and hydrogen sulfide–producing bacteria), physical (color coordinates L*, a*, and b*, and cutting strength), chemical (moisture, pH, total volatile basic nitrogen (TVB-N), peroxide value (PV), and thiobarbituric acid reactive substances (TBARS)) and sensory properties were performed every 3 days over a total of 27 days. During storage across all the treatments, L*, a*, cutting strength, pH, moisture content, and sensory scores decreased; whereas, b*, TVB-N, PV, TBARS, and microorganisms increased. However, among the various alternatives, MAP-1 had the best retention of oyster quality during storage. Based on sensory and microbiological qualities, the shelf lives in chilled storage were 9 days for control, 15 days for VP, 21 days for MAP-2 and MAP-3, and 24 days for MAP-1-treated cases.     

Blood oxygen tension and content in carp, Cyprinus carpio L., during hypoxia and methaemoglobinaemia

Carp respond to water hypoxia with an evaluation in the rate of gill ventilation. In order to characterize closer the adequate stimulus for the increase in respiratory drive specimens of carp, Cyprinus carpio L., were exposed simultaneously to moderate environmental hypoxia (P^wO²? 75mmHg, 10kPa) and elevated water nitrite concentration (089 ± 0-lmmol/l) for 24h. The differential effects of these treatments were utilized to distinguish between the responses to an immediate reduction in water and arterial Po_a (P,O²), and to the slowly developing reduction of arterial oxygen content (C^aO²) and functional oxygen saturation (S^aO²). After onset of hypoxia gill ventilation quickly increased, leading to a reduction in P_aCO₂. Slowly rising blood methaemoglobin levels resulted in a gradual decline in C^aO² and S^aO² over 24h, whereas P002 remained steady for the entire exposure period. This pattern of lowered P^aco² and P_aO₂, essentially constant for 24 h, together with the lack of any correlation with changes in C^aO², suggests PO₂ (P^a,O² and/or P^wo²) as the primary stimulus in the regulation of ventilation of carp.     

Lack of arterial PO<Subscript>2</Subscript> downregulation in Atlantic salmon (<Emphasis Type="Italic">Salmo salar</Emphasis> L.) during long-term normoxia and hyperoxia

Regulation of arterial partial pressure of O₂ (P_aO₂) in Atlantic salmon (Salmo salar) was investigated during resting conditions in normoxic and hyperoxic water. Dorsal aorta cannulated adult Atlantic salmon (1.2–1.6 kg, n = 8) were exposed to 2 week sequential periods of normoxia [16.7 ± 1.1 kPa (mean ± SD)] and hyperoxia (34.1 ± 4.9 kPa) in individual tanks containing seawater (33.7 ± 0.2 ppt) at stable temperature conditions (8.7 ± 0.7°C) and a light regime of L:D = 12:12. Tank design and sampling procedures were optimized to provide suitable shelter and current for the fish, and to allow repeated, undisturbed sampling of blood from free-swimming fish. Fish were sampled regularly through the experimental period. P_wO₂, P_aO₂, blood ion composition (Na⁺, K⁺, Cl⁻), acid–base status (pH, PCO₂, HCO₃ ⁻), haematocrit and glucose were measured. The most frequently observed P_aO₂ values were in the range of 60–80% of P_wO₂, both during normoxia and hyperoxia, and P_aO₂ values were significantly lower during normoxia than during hyperoxia. Blood pH, PCO₂ and HCO₃ ⁻ were significantly elevated during hyperoxia, while, Na⁺, Cl⁻ and Hct were significantly lower. K⁺ and glucose showed no significant differences. This study demonstrates a lack P_aO₂ regulation in Atlantic salmon to low partial pressures, in contrast to previous reports for many aquatic gill breathing animals. Both during normoxia and hyperoxia, P_aO₂ reflects P_wO₂, and alterations in external PO₂ consequently result in proportional arterial PO₂ changes. Physiological adaptation to hyperoxia, as illustrated by changes in several blood parameters, does not include down-regulation of P_aO₂ in Atlantic salmon. The lack of P_aO₂ regulation may make Atlantic salmon vulnerable to the oxidative stress caused by increased free radical formation in hyperoxic conditions.     

挤压蒸煮操作参数对鱼蛋白高水分模拟产物组织化效果的影响

对高水分鱼蛋白的挤压组织化进行研究, 以双轴挤压设备操作参数中的进料水分、腔体温度、螺杆转速、进料速率和电机转速为影响参数, 挤压模拟产物的纤维化程度、硬度、弹性、咀嚼性和色泽为响应因素, 通过中心组合设计及响应面分析法, 探讨了高水分挤压重组技术对鱼蛋白模拟肉类产物特性的影响。结果表明: 首先, 高水分组织化模拟产物具有明显的天然肉类的纤维结构、方向性、弹性和口感。其次, 进料水分对产物的纤维化度、硬度和咀嚼性影响相当显著(P<0.01), 对模拟物色泽中的L^*和a^*影响显著(P<0.05), 进料水分的增加使产物的纤维化度、硬度、咀嚼性和a^*降低, 但提升产物 L^*; 腔体温度对产物的咀嚼性和a^*影响特别显著(P<0.01), 对硬度影响显著(P<0.05), 升高腔体温度会增加的产物咀嚼性和a^*, 硬度则先上升后下降; 进料速率对产物的纤维化度影响极其显著(P<0.01)。     

Quality Evaluation of Grass Carp (Ctenopharyngodon idella) Protein Concentrate Supplemented Noodles

ABSTRACT

The aim of the present study was to evaluate the quality of wheat flour noodles supplemented with 0%, 10%, 20% and 30% grass carp protein concentrate (GCPC). Proximate composition, color analyses, cooking properties (cooking time, cooking loss, swelling index and water absorption index), texture profile analyses (TPA), and sensory evaluations were performed. Significant (p ≤ 0.05) increases in the crude protein (18.94–35.19%), crude fat (0.88–1.06%), and ash (0.89–1.02%) were recorded for GCPC supplemented cooked noodles. Brightness (L*), redness (a*) and yellowness (b*) of GCPC 10–30% fortified cooked noodles was recorded as 77.00–69.97, 1.50–2.81 and 19.08–22.25, respectively. Cooking loss (CL) and optimal cooking time were significantly (p ≤ 0.05) increased with increased level of GCPC from 0%-30%, with readings of 6.13% ?8.90% and 7.53–11.77 min, respectively. Swelling and water absorption indices showed a decreasing trend at 2.33–1.77 and 102.6–78.49%, respectively. A significant (p ≤ 0.05) decreasing trend in hardness (24.50–19.03N) was observed for cooked noodles with increased level of GCPC, while the remaining TPA parameters were significantly different at p> .05. Sensory analyses showed higher preference for control noodles and noodles fortified with 10% GCPC.     

Partial replacement of fishmeal with corn protein concentrate in diets for rainbow trout (Oncorhynchus mykiss): Effects on growth performance,physiometabolic responses,and fillet quality

An 8‐week feeding trial was run to investigate the replacement of fishmeal with corn protein concentrate (CPC; Empyreal^®) in rainbow trou (100.5 ± 2.3 g) diet. Fishmeal was increasingly replaced with 0 (Control), 30 (CPC₃), 60 (CPC₆), 90 (CPC₉) and 120 (CPC₁₂) g/kg CPC. The results showed that the substitution of fishmeal with CPC up to 90 g/kg did not cause significant differences in the growth indices as compared to the control group, while further replacement resulted in the reduction of the growth performance. The fillet crude protein showed no significant difference between the control diet and diets containing up to 90 g/kg CPC (p > .05). Serum biochemical parameters such as albumin and glucose did not change notably, while the highest levels of alanine aminotransferase and lactate dehydrogenase were seen in the CPC₁₂ group (p < .05). Also, serum lysozyme activity was increased with the elevation of dietary CPC up to 90 g/kg (p < .05). The redness and yellowness of the fillet were markedly elevated with the dietary incorporation of CPC (p < .05). Taken together, the optimum range of fishmeal substitution with CPC was 81.0–82.2 g/kg CPC in rainbow diet based on the broken‐line regression analysis.     

Effect of Traditional and Liquid Smoke on the Quality of Sea Catfish Sausages (Sciades herzbergii,Bloch, 1794)

ABSTRACT

Smoking is a technique used to improve the sensory attributes and increase the shelf life of fish. The objective of the present study was to evaluate the nutritional, physicochemical, microbiological, and sensory characteristics of sausages made with sea catfish (Sciades herzbergii) fillets subjected to the traditional and liquid smoking processes. The traditionally smoked sausages showed lower (p < .05) moisture content and higher protein, fat, and mineral levels, higher weight loss during processing, higher pH, higher a* (red intensity), and lower L* (luminosity) values. The percentage of shrinkage, water holding capacity, water activity, hardness, cohesiveness, and elasticity were not influenced (p > .05) by the smoking methods tested. The microbial counts of both treatments were in compliance with the current Brazilian legislation. The sensory acceptance of the liquid smoked sausages was higher (p < .05) when compared to the traditionally smoked sausages for the attributes of color, aroma, texture, flavor, and overall acceptance, with scores ranging from 6 (liked slightly) to 7 (liked moderately). Between the two smoking methods tested, liquid smoking presented better sensory acceptance, easier execution, greater process control, and less environmental impact; thus, it is a viable alternative to the traditional smoking of sea catfish (Sciades herzbergii) sausages.     

Effects of Water Hardness and Calcium: Magnesium Ratios on Reproductive Performance and Offspring Quality of Macrobrachium rosenbergii

This study evaluated the effect of specific calcium and magnesium ratios at two hardness values on reproductive performance and offspring quality of Macrobrachium rosenbergii brood‐females. Hatchery water containing 110.5 mg/L CaCO3 hardness was considered baseline as it has been used successfully to hatch and rear larvae and was used as the control treatment. At each hardness value of 150 and 190 mg/L CaCO₃, four experimental water treatments were made in triplicate. Each treatment was adjusted using soluble salts (CaCl₂·H₂O, MgSO₄·7H₂O, and MgCl₂·6H₂O) to provide the hardness and calcium to magnesium ratios of 0:20, 20:80, 50:50, and 80:20 needed. Each of the experimental tanks (140 L) were stocked with six females and one male. The results indicated that both hardness and Ca:Mg ratios affect brood‐female reproductive qualitative parameters such as intermolt period, egg hatchability, egg dry weight, and egg‐clutch somatic index (ESI) parameters (P < 0.05) but not fecundity and eggs per spawn. The results revealed that brood‐females at 150 mg/L hardness showed greater reproductive performance than at 190 and 110.5 mg/L hardness. The findings also demonstrated that the treatment 50Ca50Mg at 150 mg/L hardness with 38.8 mg/L calcium and 12.9 mg/L magnesium had optimum reproductive performance and offspring quality for M. rosenbergii brood‐females.     

Changes in arterial PO₂, physiological blood parameters and intracellular antioxidants in free-swimming Atlantic cod (Gadus morhua) exposed to varying levels of hyperoxia

Free-swimming Atlantic cod (Gadus morhua) were exposed to water oxygen pressures (P _wO₂) ranging from 18.1 to 41.5 kPa and sampled for blood using an indwelling caudal artery cannula. Arterial blood oxygen pressure (P _aO₂) increased with increasing P _wO₂, from 12.0 kPa in normoxia (18.1 kPa) to 34.2 kPa in the highest hyperoxic level tested (41.5 kPa). Blood CO₂ pressure and plasma bicarbonate concentration increased with P _wO₂, indicating reduced ventilation with increased P _wO₂. Plasma glucose, sodium and potassium were not affected by water oxygen level. Blood oxidative stress biomarkers, reduced glutathione, oxidized glutathione and the oxidative stress index (ratio between oxidized and total glutathione) differed intermittently between normoxia and hyperoxia. The oxidative stress index was higher in the blood of exposed compared to unexposed control cod. Together with elevated P _aO₂, these findings suggest increased production of reactive oxygen species and increased oxidative stress in Atlantic cod exposed to hyperoxia.     

Apparent digestibility of some nutrient sources by juvenile mud crab, Scylla serrata (Forskal 1775)

As part of preliminary work aimed at the development of a formulated diet for the mud crab, Scylla serrata, an experiment was conducted with juvenile mud crabs (95.65±2.17 g) to determine apparent digestibility coefficients (ADC) for cellulose, fish meal, shrimp meal, blood meal, soybean meal, wheat flour and cod liver oil. Apparent digestibility coefficients for dry matter (ADC_dm), energy (ADC_energy) and protein (ADC_protein) were in the ranges 70.0–95.7%, 77.4–97.1% and 57.7–97.9% respectively. Soybean meal had the highest ADC_dm and wheat flour had the lowest value (P<0.05), while the ADC_dm for fish meal, blood meal and shrimp meal were not different (P≥0.05). Similarly, soybean meal had the same ADC_energy as that of fish meal, but higher than those of cod liver oil, blood meal and shrimp meal (P<0.05). Moreover, the ADC_protein for blood meal or shrimp meal were not significantly different from fish meal (P≥0.05); nevertheless, they were lower than that of soybean meal and higher than that of wheat flour (P<0.05). Of significant interest was the ADC_dm (78.0%) and ADC_energy (77.4%) for cellulose, which indicates that plant‐based nutrient sources may well be a useful component of formulated diets for mud crabs.     

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.