Ovarian fluid pH enhances motility parameters of rainbow trout (Oncorhynchus mykiss) spermatozoa

All evidence to date suggest that sperm motility is the primary determinant of fertilization success in externally fertilizing fish species. Ovarian fluid, which comprises 10–30% of the total egg volume in salmonids, enhances sperm motility with respect to swimming speed, trajectory and the duration of movement. It was recently demonstrated that there is individual variability in sperm motility enhancing potential of ovarian fluid of particular females. In the present study we examined the effect of particular ovarian fluids collected from 31 females on the sperm motility parameters of one male of rainbow trout (Oncorhynchus mykiss) using computer-assisted sperm analysis (CASA). During our experiment we also monitored the pH of ovarian fluid. We found that particular fluids differed in the ability to activate spermatozoa; sperm remained immotile in four fluids and exhibited 50–100% motility in 27 samples. The percentage of motile sperm, velocity and duration of movement positively correlated with ovarian fluid pH (r² = 0.34–0.62). These data strongly suggest that the pH of the ovarian fluid is the primary determinant of sperm motility in rainbow trout under natural conditions of fertilization.     

Evaluation of krill (Euphausia superba) meal as a partial replacement for fish meal in rainbow trout (Oncorhynchus mykiss) diets

We studied partial replacement of fish meal (FM) by krill meal (KM) and how fluoride from KM enriched-muscles and bones of rainbow trout reared in freshwater affected these fish. Diets that replaced FM with KM at proportions of 0, 7, 15 and 30% (control, KM7, KM15, and KM30) were fed to groups of rainbow trout for 92 days and growth was observed. In fish fed KM7 and KM15, weight gain (WG), feed intake (FI) and specific growth rate (SGR) were unchanged compared with fish fed the control diet, but in fish fed KM30, WG, FI and SGR significantly decreased. After the experiment, fluoride concentration in dorsal muscles of each experimental group was below the detected limit (1 mg/kg), but in vertebral bones, the fluoride concentration increased with each increase in KM inclusion in the diets: 490 mg/kg (control), 755 mg/kg (KM7), 1100 mg/kg (KM15), and 2400 mg/kg (KM30). Tissue specimens of liver of each experimental group had no histopathological changes. Therefore, accumulation of fluoride in vertebral bones apparently adversely affected growth of the vertebral bones thus affecting the growth performance as shown by the decrease in WG, FI and SGR.     

Comparison of conventional and molecular techniques to investigate the intestinal microflora of rainbow trout (Oncorhynchus mykiss)

The concept of the use of probiotic organisms or prebiotic compounds to modify the fish gut microflora is becoming a popular topic for investigation. A major flaw in many such studies is a failure to consider fully the nature of the established microflora, which is to be modified pre-, or probiotically. Since it is widely accepted that a large proportion of bacteria are non-culturable, the use of conventional bacteriological (culture) techniques alone to investigate fish intestinal microflora may be expected to bias results. We report a study designed to investigate the normal intestinal microflora of rainbow trout (Oncorhynchus mykiss) using both conventional bacteriological and molecular methods.Over an 18 month period, the intestinal microflora of a single population of laboratory-raised rainbow trout was investigated. Bacteria isolated using bacteriological techniques were identified using the BiOLOG system and 16S rRNA gene sequencing. Dominant bacteria consistently were Aeromonas sp. and Carnobacterium piscicola, demonstrating that the microflora is stable in fish kept in defined conditions. Restriction Fragment Length Polymorphism (RFLP) and 16S rRNA gene sequence analysis was used to investigate anaerobic and non-culturable bacteria. An obligate anaerobe, Clostridium gasigenes, was shown to be among the dominating intestinal microflora.     

Automated image analysis as a tool to quantify the colour and composition of rainbow trout (Oncorhynchus mykiss W.) cutlets

The goal of this paper is to propose and evaluate automated image analysis methods for describing muscle cutlets in rainbow trout. The proposed automated image analysis methods were tested on a total of 983 scanned images of trout cutlets, and included quality traits such as fat percentage, flesh colour and the size of morphologically distinguishable subparts of the cutlet. A sub-sample of 50 images was randomly selected for manual segmentation of the cutlet, the dorsal fat depot and the red muscle and regions. The identification of these regions by manual and automatic image analysis correlated strongly (r = 0.97, r = 0.95 and r = 0.91, respectively). The estimated fat percentage obtained from image analysis, based on the area of visible fat and the colour of the cutlet flesh, correlated well with chemical fat percentage measured by mid-infrared transmission spectroscopy (MIT) (r = 0.78). The automated image analysis methods are therefore a reliable means of predicting the fat percentage of trout cutlets. Principal component analysis (PCA) loading plots were used to identify subsets of variables from the image analysis of special significance for further studies; cutlet area, dorsal fat depot area, red muscle area, back height, cutlet width, and width of left and right abdomen wall were among the variables selected. PCA loading plots of different colour variables indicated that simple statistical coefficients such as percentiles and mean values can be used to quantify different aspects of flesh colour. In conclusion, the methods presented here provide a powerful toolbox for describing important morphological structures and quality traits of trout cutlets.     

The effect of trigger depth on self-feeder utilisation, growth and the vertical distribution of tank-held rainbow trout Oncorhynchus mykiss (Walbaum)

This study investigated the effect of placing a self-feeding trigger at either a) 1 cm below the water surface or b) mid-water (35 cm below the surface), on self-feeder usage, growth, feed wastage and fin damage of juvenile rainbow trout, Oncorhynchus mykiss (Walbaum). The vertical distribution of trout was also measured for the first 31 days of self-feeding. Group-held trout (n = 10 fish group^− 1, 5 groups treatment^− 1), weighing 51.06 g ± 8.09 g (mean ± SD) were held in 200 l cylindroconical tanks (depth = 75 cm) for 62 days. Trigger placement had no significant effect upon self-feeder conditioning, and upper trigger group (UTG) and lower trigger group (LTG) fish took an average of 16 ± 7.4 days and 14 ± 9.8 days to reach a stable level of self-feeding, respectively. Specific growth rate was significantly higher in UTG fish (1.83 ± 0.20 vs. 0.95 ± 0.21 for UTG vs. LTG fish, respectively) whilst condition factor and self-feeder utilisation (ration size, 1.21 ± 0.18 vs. 0.52 ± 0.15 kg tank^− 1 for UTG vs. LTG fish) were also significantly higher in UTG fish. Trigger depth had no significant effect on size heterogeneity, mortality, feed wastage, feed conversion ratio (FCR) or the incidence of caudal and dorsal fin splitting and fin erosion. Dorsal fin splitting decreased with time in UTG but not in LTG fish. Caudal fin erosion increased with time in UTG (upper lobe only) and LTG (both lobes). The vertical distribution of fish also differed between treatments and more LTG fish preferred the lower part of the tank. Placing a self-feeding trigger at a mid-water depth can significantly limit growth, condition factor and self-feeder utilisation in juvenile rainbow trout, in addition to hindering recovery from dorsal fin erosion.     

Effects of diets containing a bacterial protein meal on growth and feed utilisation in rainbow trout (Oncorhynchus mykiss)

Triplicate groups of rainbow trout with initial weight 361 g were fed either a fish meal based control diet or diets containing 9, 18 or 27% bacterial protein meal (BPM) or 9% of an autolysate (AU) of the BPM. No significant treatment effects were found on specific growth rates (SGR), feed intake, feed efficiency ratio (FER), or retention of nitrogen, amino acids or energy. The apparent digestibility coefficients (ADC) of nitrogen, energy and most indispensable amino acids decreased when BPM was included in the diet. The ADC of lipid, sum of amino acids, arginine, lysine, threonine and most of the dispensable amino acids were reduced at 27% BPM inclusion compared to the control, 9% and 18% BPM diets. None of the ADC estimated was different in the 9% AU diet compared to the 9% BPM diet. The loss of nitrogen and energy in faeces per kg gain increased as the dietary BPM or AU levels increased, and the energy used for activity and maintenance was higher in fish fed the 27% BPM diet than in fish fed the other diets (P < 0.05). There were no significant differences in the urea concentrations in plasma, liver and muscle, whereas the uric acid level in plasma was elevated in trout fed the 27% BPM diet. Histological evaluation of tissue from the stomach, pyloric caeca, mid-intestine and distal intestine did not reveal any diet-related morphological changes.In conclusion, no significant differences in growth and feed efficiency were found in the rainbow trout fed diets containing up to 27% BPM, and the AU did not increase fish performance compared to the BPM. Based on the data from this study, at levels up to 27% dietary inclusion, BPM is a good replacement for fish meal in diets for rainbow trout.     

Morphometric evaluation of changes in the digestive tract of rainbow trout (Oncorhynchus mykiss) due to fish meal replacement with soy protein concentrate

Effects of the complete replacement of fish meal (FM) by soy protein concentrate (SPC) in high-energy diets (23 MJ kg^− 1 gross energy) on intestinal and liver histology were investigated in rainbow trout (Oncorhynchus mykiss). We developed a novel morphometric method to quantify the changes at the macro- and micromorphology level. Fish were acclimatized to the diet for 90 d and were then fed 1.0 g kg BW^− 1 d^− 1 once per day for 14 d before 10 fish per diet were randomly sampled, 6 h after their last meal. Fold height, epithelium length, stroma proportion of the proximal and distal intestines were not affected by the diet. No significant diet effect was detected on the features of the valve in the distal intestine. Fold height was linked to epithelium length in the proximal and distal intestines and this relationship was not modified by FM replacement. Enterocyte height and width were lower in SPC-fed fish in the distal intestine, but in the proximal intestine their morphology was not affected by the diet. There was no diet effect on the number of cells infiltered between the enterocytes in the proximal and distal intestines. The enterocyte nucleus was closer to the apex in the proximal and distal intestines in SPC-fed fish, but the features of the nucleus were not affected by the diet. The mean hepatocyte volume was on an average 36% lower in SPC-fed fish and was positively correlated to the hepatosomatic index for fish fed this diet only. In conclusion, SPC used in the present study did not either cause inflammatory reaction of the gut nor affected the epithelium surface. We suggest that the modifications due to SPC are linked to variations in the metabolic status of the enterocyte.     

虹鳟IgM重链恒定区的表达及兔抗血清的制备

为了能够成功表达虹鳟IgM,本研究利用生物信息学软件对虹鳟IgM的亲水性及抗原性进行了分析,根据GenBank收录的虹鳟IgM重链恒定区,参照生物信息学分析结果,设计用于扩增截短的IgM基因的引物,以虹鳟头肾RNA提取物为模板,利用RT-PCR方法扩增虹鳟截短的IgM重链恒定区部分基因片段,连接原核表达载体pET-27b,利用大肠杆菌Rosetta进行表达。SDS-PAGE及HPLC结果显示,纯化后截短的IgM大小约为47.7 ku,且纯度达到90%。利用其制备兔抗血清后ELISA分析结果显示,所制备的兔抗血清与本研究所表达的截短IgM蛋白的反应效价为1∶40 000,与虹鳟血清提取的全长IgM反应效价为1∶20 000并且呈现出抗原计量依赖性。研究表明,重组IgM蛋白与虹鳟血清中的天然IgM重链恒定区具有近似的结构,利用其所制备的兔抗血清能够与虹鳟鱼体中的天然IgM发生特异性反应。     

Oral pharmacological treatments for ichthyophthiriosis of rainbow trout (Oncorhynchus mykiss)

The aim of this work was to explore the efficacy of a veterinary drug, Triclabendazole (5-chloro-6-(2, 3-dichlorophenoxy)-2-methylthio-1H-benzimidazole), in an inclusion complex with β-cyclodextrin as a suitable treatment for parasitic diseases caused by Ichthyophthirius multifiliis in rainbow trout. The efficacy was determined by the reduction in the infection intensity. The complexes were prepared by the kneading method and were characterized by DSC and X-ray diffractometry. The selected stoichoimetry was 1:3 because of the higher percentage of Triclabendazole complexed with cyclodextrin. Administration of Triclabendazole and complex was carried out by including appropriate doses in animal feed. Our studies suggest that the Triclabendazole–cyclodextrin complex results in a reduction in the infection degree and trophont size is decreased in the animals treated. The oral treatment of Triclabendazole in inclusion complexes may be an alternative to bath treatments in trout farming.     

Effects of soybean meal based diet on growth performance, gut histopathology and intestinal microbiota of juvenile rainbow trout (Oncorhynchus mykiss)

Effects of soybean meal (SBM) based diet on growth performance, histology of the intestinal epithelium and on the gut microbiota of juvenile rainbow trout (Oncorhynchus mykiss) were investigated on two trials lasting for 8 weeks (Trial I) and 18 weeks (Trial II). The microbiological characterization was done both with conventional plating techniques, biochemical profiling and length heterogeneity analysis of PCR amplified 16S rDNA (LH-PCR).Typical histological changes were found after 18 weeks of SBM feeding (Trial II). Mean height of simple foldings were significantly higher within the group fed with fish meal (FM) based diet. These changes were not, however, reflected in the appearance, behavior and weight gain of the fish, although the feed conversion rate (FCR) was higher, compared to fish fed with the traditional FM feed.In both SBM and FM groups the counts of cultivable intestinal bacteria dropped within the first 4 weeks of feeding (Trial I). Subsequently, the bacterial numbers increased in the FM group, but not in the SBM group by the 8th week of the trial. The LH-PCR data suggested also that diet-related qualitative changes in the microbiota had occurred (Trial II). The main identified bacteria were mainly representatives of the genera Aeromonas, Sphingomonas and Chryseomonas, and among the lactic acid bacteria, Lactococcus and Lactobacillus.Future research will be directed to the identification and eventual elimination the SBM-associated factors involved in the inflammatory responses and unfavorable FCR, in particular by modifying the intestinal microbiota.     

虹鳟肠炎红嘴病病理模型的构建

为探讨鲁氏耶尔森菌侵染虹鳟的致病机制,本实验建立了鲁氏耶尔森菌感染虹鳟引起的肠炎红嘴病的病理模型,制定相应的临床症状及组织病理学评分系统,并对该模型进行研究。将43尾平均体质量约为12 g的健康虹鳟随机分成5组:3个实验组(n=30)、对照组(n=10)和哨兵组(n=3)。3个实验组分别采用2.0×106、2.0×107和2.0×108 CFU/m L的鲁氏耶尔森菌感染浓度,通过腹腔注射方式进行人工感染试验。对感染鲁氏耶尔森菌的虹鳟肠、肝脏、脾脏和肾脏组织进行镜检及临床症状、剖检病变判断,结合细菌学检测,按制定的评分系统评价各组肠炎红嘴病造模效果,确定最佳造模方案。结果显示,各攻毒组虹鳟感染后72 h均出现不同程度死亡,临床症状表现为红嘴、肛门红肿、鳍(胸鳍、腹鳍、臀鳍)等出现不同程度充血,下颌部、腹部出现出血点等。组织病理学可见肝脏、脾脏、肾脏及肠组织均有炎性细胞浸润现象出现,肝细胞、肠上皮细胞和肾小管上皮细胞等实质细胞变性、坏死,脾脏部位淋巴细胞减少、红细胞死亡堆积。综合各组得分发现,2.0×107 CFU/m L组的鲁氏耶尔森菌感染虹鳟造模效果最佳,患病虹鳟的临床症状显著且组内差异较小,病程迁延较长,便于研究。研究表明,对体质量约12 g的虹鳟幼鱼腹腔注射0.1 m L浓度为2.0×107 CFU/m L的鲁氏耶尔森菌可成功构建肠炎红嘴病病理模型。     

Fat or lean? The quantitative genetic basis for selection strategies of muscle and body composition traits in breeding schemes of rainbow trout (Oncorhynchus mykiss)

Quantitative genetic analyses of fish composition have been strongly biased towards lipid deposition, rather than protein deposition. This is partly at odds with desires of the modern aquaculture industry, to improve the efficiency of lean growth. Using a quantitative genetic approach, we examined the selection potential in both protein and lipid components of wet weight growth in rainbow trout over a two-year growth period. Two diet treatments were applied to test the hypothesis that an experimental, high protein, low lipid diet (HP) would enhance selection potential compared to the current modern, normal protein, high lipid diet (NP). We found that lipid traits (lipid body weight, percent muscle and body lipid; h² = 0.40) were more heritable than corresponding protein traits (protein body weight, percent muscle and body protein; h² = 0.18), indicating a higher selection potential for lipid traits. The results revealed further that breeding for improved lipid composition over the whole growth period is easier than for protein composition. This was shown by the high favourable genetic correlations between differently aged fish for lipid traits. In contrast, the respective correlations for protein traits were low or even negative. Similarly, the genetic correlations between muscle and body composition were higher for lipid than for protein, enhancing selection efforts to change lipid traits. Heritabilities increased with age, implying that selection practiced on old (> 800 g) rather than young (< 60 g) fish should be more effective in achieving a compositional response. Although the diet had a significant effect on the composition traits, there was no general trend for diet differences in heritabilities of either protein or lipid traits. Thus, the hypothesis of increased selection potential on HP diet was not supported. In conclusion, lipid traits are both more variable and exhibit more favourable genetic architecture for selection compared to protein traits.     

Abnormal swimming behavior and increased deformities in rainbow trout Oncorhynchus mykiss cultured in low exchange water recirculating aquaculture systems

Two studies were conducted to evaluate rainbow trout Oncorhynchus mykiss health and welfare within replicated water recirculating aquaculture systems (WRAS) that were operated at low and near-zero water exchange, with and without ozonation, and with relatively high feed loading rates. During the first study, rainbow trout cultured within WRAS operated with low water exchange (system hydraulic retention time (HRT) = 6.7 days; feed loading rate = 4.1 kg feed/m³ daily makeup flow) exhibited increased swimming speeds as well as a greater incidence of “side swimming” behavior as compared to trout cultured in high exchange WRAS (HRT = 0.67 days; feed loading rate = 0.41 kg feed/m³ daily makeup flow). During the second study, when the WRAS were operated at near-zero water exchange, an increased percentage of rainbow trout deformities, as well as increased mortality and a variety of unusual swimming behaviors were observed within WRAS with the highest feed loading rates and least water exchange (HRT ≥ 103 days; feed loading rate ≥ 71 kg feed/m³ daily makeup flow). A wide range of water quality variables were measured. Although the causative agent could not be conclusively identified, several water quality parameters, including nitrate nitrogen and dissolved potassium, were identified as being potentially associated with the observed fish health problems.     

Low feed pellet water stability and fluctuating water salinity cause separation and accumulation of dietary oil in the stomach of rainbow trout (Oncorhynchus mykiss)

Regurgitation (belching) of oil is a problem in sea farmed rainbow trout kept in water with fluctuating salinity. This often coincides with abdominal distension syndrome, which is associated with osmoregulatory stress and lipid indigestion. The present study investigated combined effects of water stability in extruded feeds and fluctuating water salinity on feed consumption, growth, nutrient digestibility, gastrointestinal transit, and accumulation of water and oil in the stomach of rainbow trout. Diets were produced with high or low water stability, which were characterised by a novel water stability test. In an initial 84 days growth experiment, each diet was fed to six groups of 772 g trout, of which three tanks were supplied with full-strength seawater, and three tanks were fluctuated between seawater and freshwater (7 h per day during 3 successive days per week). No significant effects were seen, although the feed intake appeared slightly lowered by low dietary water stability at fluctuating salinity. In a second experiment, each diet was fed to four groups of 1 kg trout, of which two tanks were supplied with full-strength seawater, and two tanks were fluctuated between seawater and brackish water (17‰ 7 h per day daily). Low water stability of the diet resulted in accumulation of oil in the stomach, and this response was worsened when the salinity of the rearing water fluctuated. It also corresponded with reduced lipid digestibility. Consequently, low water stability of the diet caused an oil separation in the stomach that may result in oil-belching in rainbow trout suffering from osmoregulatory stress.     

Phosphorus utilization in rainbow trout (Oncorhynchus mykiss) fed practical diets and its consequences on effluent phosphorus levels

Excessive dietary phosphorous (P) concentrations in effluents from aquaculture present a major environmental problem. We therefore studied the effect of dietary P and vitamin D₃ on P utilization by rainbow trout-fed practical diets and on P concentrations in the soluble, particulate and settleable components of the effluent from fish tanks. Rainbow trout (average weight: 78 g, initial biomass: 13 kg in 0.7 m³ tanks) were fed for 11 weeks, practical diets that varied in total P, available P, and vitamin D₃ concentrations. Soluble, particulate (10–200 μm) and settleable (>200 μm) P in the effluent were sampled every 0.5–6 h for 1–3 days in the third and eleventh weeks of the experiment. Trout in all diets more than doubled their weight after 11 weeks. Increasing the concentrations of available dietary P from 0.24% to 0.88% modestly enhanced growth rate. Feed conversion ratio (FCR) and biomass gain per gram P consumed decreased as dietary P concentrations increased. Carcass P, daily P gain, and plasma P concentrations were lower in fish fed with low P diets. Soluble P concentrations in the effluent peaked immediately after and again 4–6 h after feeding, and is a linear function of available dietary P. No soluble P would be produced during consumption of diets containing less than 0.22±0.02% available P. Above this dietary concentration, soluble P would be excreted at 6.9±0.4 mg/day/kg for each 0.1% increase in available dietary P. Particulate P concentrations in the effluent were independent of dietary P concentrations. Settleable, presumably fecal, P concentrations tended to increase with dietary P concentrations. In trout fed with low P (0.24% available P, 0.6% total P) diets, 60% of total dietary P were retained by the fish and the remaining 40% were excreted in the effluent as settleable P (20–30%) and particulate or soluble P (10–20%). In trout fed with high P (0.59–0.88% available P; 0.9–1.2% total P) diets, 30–55% of total dietary P was retained by fish, and the remaining 15–25% appeared in the effluent as settleable P, 20–55% as soluble P, and 5–10% as particulate P. Vitamin D₃ did not affect fish growth nor effluent P levels. Physicochemical management of aquaculture effluents should consider the effect of diets on partitioning of effluent P, the peaks of soluble P concentration following feeding, and the contributions of particulate P to total P in the effluent. Increasing our understanding of how dietary P is utilized and is subsequently partitioned in the effluent can contribute significantly towards alleviating this important environmental and industry problem.     

Occurrence of two forms of Y chromosome in rainbow trout (Oncorhynchus mykiss) males from Rutki strain

Morphologically differentiated sex chromosomes are found in only few salmonid species. Some populations of rainbow trout, Oncorhynchus mykiss, exhibit chromosomal polymorphism related to sex. We found sex-related chromosomal polymorphism in fish from the synthetic Rutki strain, Poland, in approximately 85% (n = 22) of examined males (XY-like) whereas the remaining males (n = 4) possessed chromosomes similar to these observed in females (XX-like). To investigate whether males possessing XX-like chromosomes were genotypic males or genotypic females with altered phenotypic sex, androgenetic progeny of four males (representing both XY-like and XX-like forms, n = 2 + 2) was examined. Androgenetic progeny (F₁) of all four fathers consisted of both phenotypic females and males. F₁ male progeny of two fathers showed XX-like chromosomes whereas F₁ male progeny of the other two fathers possessed YY-like (supermale) chromosomes. F₁ were reared further until they were sexually mature. Two males from each of four F₁ families were used to produce F₂ androgenetic and control F₂ generation. All F₂ individuals, androgenetics and control, were phenotypic males at sexual maturation. The results indicate that males possessing XX-like chromosomes are genetic males and they are not sex-reversed females. Thus, the Y chromosome can exist in different morphological forms in farmed rainbow trout. The Y^S chromosome (shorter form, unlike the X chromosome) has a shorter or absent p-arm and lacks the pericentromeric cluster of AT-rich chromatin and the 5S rDNA sequences that are found in the Y^L chromosome (longer form, like the X chromosome).     

Diet energy source affects lysine utilization for protein deposition in rainbow trout (Oncorhynchus mykiss)

We have previously shown that lysine utilization for body protein deposition (PD) in rainbow trout was affected by digestible energy (DE) content of the diet. When lysine intake limits PD, additional DE intake from fish oil improves efficiency of lysine utilization for PD. It is unclear whether other energy-yielding nutrients have the same effect on lysine utilization. Different energy sources that may be converted to different tricarboxylic acid (TCA) cycle metabolic intermediates can have different abilities to spare lysine for PD. An experiment was therefore carried out to examine the effects of different energy-yielding nutrients, on growth, nitrogen gain and lysine utilization by rainbow trout. Fish weighing 5.0 g ± 0.1, were fed diets with either limiting (1.5%) or marginally adequate (2.0%) lysine levels. Acetyl-CoA precursors (fish oil), pyruvate precursors (mixture of alanine, serine, glycine, and cystine) and α-ketoglutarate + oxaloacetate precursors (mixture of aspartate, glutamine and glutamate) were then added to the control diets (at the expense of raw corn starch) to produce a series of experimental diets with 20 MJ DE. Fish were pair-fed for 16 weeks and then to satiation for an additional 6 weeks. Results suggest that different energy sources affect lysine utilization differently. When feed intake was similar, additional DE from pyruvate and α-ketoglutarate/oxaloacetate precursors did not improve PD. When lysine was limiting, pyruvate precursors reduced feed intake and PD. Fatty acids, which similarly to lysine may be converted to acetyl-CoA, appear to be more effective in sparing lysine for PD than other metabolic substrates that have different entry points into the TCA cycle. Rainbow trout appears to have a higher tolerance for an excess of amino acids that are α-ketoglutarate/oxaloacetate precursors (glu, gln, asp) than pyruvate precursors.     

Use of treated mine water for rainbow trout (Oncorhynchus mykiss) culture: a production scale assessment

In previous proof-of-concept work, it was shown that the use of treated coal mine water for rainbow trout (Oncorhynchus mykiss) culture in a cage was technically feasible, though only a 50-fish bioassay was grown and no work on production-related issues was conducted. To further advance the use of treated mine water, an under-utilized water resource throughout Mid Appalachia, work was conducted to assess the effects of using treated coal mine water for the intensive production of rainbow trout in a flow-through system. During this study, comprehensive water quality data were collected to supplement fish weight and length data taken during routine monthly sampling events. The 8000 fish grew well in the raceway system over the 9 months of production, where a feed conversion ratio of 1.4 and a condition factor of 5.1 × 10⁻⁴ were measured with stocking and harvest densities of 26.4 and 50.2 kg/m³, respectively. Further, total net production was 3275 kg (7220 lb) with 98.6% survival. Throughout the study, dissolved ion concentrations (Fe, Al, Mg, Ca, and SO₄) often exceeded recommended tolerance limits. Further, elevated ammonia nitrogen concentrations generated from a component of the mine water-treatment process were identified as a potential limiting factor for aquaculture development. However, when the non-ideal effects of high ionic strength and the speciation of dissolved metal–ligand complexes were taken into account, the concentrations of free metal ions were within recommended tolerance limits.     

Antioxidant processes are affected in juvenile rainbow trout (Oncorhynchus mykiss) exposed to ozone and oxygen-supersaturated water

Two groups of juvenile rainbow trout (Oncorhynchus mykiss) were exposed for 4 h to either hyperoxic (>40 mg O₂/l) or ozonised (5.2 μg O₃/l) water containing supersaturated oxygen. Gill, liver, blood cells and plasma were taken 1, 5, 12, 24 and 48 h following the exposure periods and antioxidant responses and oxidative damage studied in terms of, respectively, antioxidant enzyme activities/glutathione status and lipid peroxidation. Observed biochemical changes were significant at p<0.05. Ozonation elevated oxidised glutathione (GSSG) levels, increased lipid peroxidation and decreased reduced glutathione (GSH) levels in gills 1 h following exposure, which indicate oxidative stress. However, the longer-term effects (48 h) following ozone exposure resulted in increased GSH levels in both gills and liver and, measured as oxidative stress index (OSI), were indicative of enhanced potential of tissues to resist oxidative stress. Ozonation also resulted in elevated activity of superoxide dismutase (SOD) at 5–12 h following exposure in gills compared to 24–48 h in liver, indicating either differential regulation and time-courses of response, or an earlier impact of ozonolysis products on gills than liver. In contrast, catalase activity was elevated in both gills and liver at 24 h by the effects of hyperoxia alone. Hyperoxia also decreased GSSG levels in both gills and liver, but had no effect on lipid peroxidation. Increases were seen in the activities of selenium-dependent glutathione peroxidase as a result of ozonation (gills; 5 and 24 h) and hyperoxia (liver; 1 h), and in total GPX (Se-dependent and independent) as a result of ozonation (both tissues; 48 h), but no effects were seen on glutathione reductase (GR) in either tissues. Levels of GSH were increased in blood cells at various times following hyperoxia. Overall, the results show (i) differential antioxidant and pro-oxidant effects of ozonation compared to hyperoxia, (ii) gills and possibly blood as the first line of impact and defence, with later effects on liver, and (iii) that even after 24–48 h following ozone exposure, all antioxidant defences had not returned to pre-exposure values.