Evaluating the effects of prolonged peracetic acid dosing on water quality and rainbow trout Oncorhynchus mykiss performance in recirculation aquaculture systems

Peracetic acid (PAA) is an effective disinfectant/sanitizer for certain industrial applications. PAA has been described as a powerful oxidant capable of producing water quality benefits comparable to those expected with ozone application; however, the water oxidizing capacity of PAA in aquaculture systems and its effects on fish production require further investigation, particularly within recirculation aquaculture systems (RAS). To this end, a trial was conducted using six replicated RAS; three operated with semi-continuous PAA dosing and three without PAA addition, while culturing rainbow trout Oncorhynchus mykiss. Three target PAA doses (0.05, 0.10, and 0.30 mg/L) were evaluated at approximately monthly intervals. A water recycle rate >99% was maintained and system hydraulic retention time averaged 2.7 days. Rainbow trout performance metrics including growth, survival, and feed conversion ratio were not affected by PAA dosing. Water quality was unaffected by PAA for most tested parameters. Oxidative reduction potential increased directly with PAA dose and was greater (P < 0.05) in RAS where PAA was added, indicating the potential for ORP to monitor PAA residuals. True color was lower (P < 0.05) in RAS with target PAA concentrations of 0.10 and 0.30 mg/L. Off-flavor (geosmin and 2-methylisoborneol) levels in culture water, biofilm, and trout fillets were not affected by PAA dosing under the conditions of this study. Overall, semi-continuous PAA dosing from 0.05-0.30 mg/L was compatible with rainbow trout performance and RAS operation, but did not create water quality improvements like those expected when applying low-dose ozone.     

Effects of traditional rainbow trout (Oncorhynchus mykiss) breeding on dissolved organic nitrogen pools and microbial activity in the water

Seasonal effects of rainbow trout (Oncorhynchus mykiss) breeding in traditional, flow‐through ponds on abundance and activity of bacteria, and on pools and cycling of dissolved free and combined amino acids (DFAA and DCAA), were studied in three aquaculture systems in Denmark. The fish breeding was found to increase both abundance and production of bacteria by about 60% (annual average of all three systems). The bacterial production correlated positively with temperature, and was 10 to 60‐fold higher in summer than winter. Concentrations of DFAA (range: 45–690 nM) increased by 40–350% (mean of 89%) during passage in the systems. The bacterial uptake of DFAA was stimulated by 42% (annual average value of the three systems) between inlets and outlets. Uptake of DFAA was estimated to sustain from 45% (C) and 70% (N) of the bacterial C and N demand. Concentrations of DCAA, e.g., proteins and peptides, varied from 600 to 3900 nM, and increased on average 89% during passage in the three systems. Bacterial capacity for utilization of DCAA was determined as leucine peptidase activity and related to the bacterial density. The cell‐specific peptidase activity was, on average, 103% higher at outlets than inlets. Changes in the peptidase activity did not correlate with variations in DCAA pools or the bacterial production. Concentrations of ammonium, urea and phosphate increased on average by 88%, 103% and 66%, respectively, during passage in the three systems, whereas no changes were observed for nitrate. Our study shows that traditional fish breeding impacts pools and cycling of dissolved organic N, as well as bacterial dynamics. The short residence time of water in the ponds (3–6 h) implies that most of the nutrients produced in the systems were discharged into the downstream water, rather than assimilated by bacteria within the systems.     

A factorial model to predict phosphorus waste output of rainbow trout (Oncorhynchus mykiss)

Minimizing phosphorus (P) wastes is considered to be a key factor for environmental sustainability of freshwater aquaculture operations in many parts of the world. A factorial P model, consisting of digestibility, whole-body P deposition, P waste output and limnological transformation sub-models, was constructed to simulate the effects of different dietary P sources and levels on P utilization in salmonids. This factorial P model was developed based on information from the literature for rainbow trout ( Oncorhynchus mykiss ). This factorial model runs on the platform of a fish bioenergetics model that provides dynamic estimates of feed intake of salmonids based on diet composition and growth rate. Simulations suggest that this model can potentially be a useful tool for waste output management of salmonid culture operations.     

Puffy skin disease (PSD) in rainbow trout,Oncorhynchus mykiss (Walbaum): a case definition

Puffy skin disease (PSD) is a disease that causes skin pathology in rainbow trout, Oncorhynchus mykiss (Walbaum). Incidence of PSD in UK fish farms and fisheries has increased sharply in the last decade, with growing concern from both industry sectors. This paper provides the first comprehensive case definition of PSD, combining clinical and pathological observations of diseased rainbow trout from both fish farms and fisheries. The defining features of PSD, as summarized in the case definition, were focal lateral flank skin lesions that appeared as cutaneous swelling with pigment loss and petechiae. These were associated with lethargy, poor body condition, inappetance and low level mortality. Epidermal hyperplasia and spongiosis, oedema of the dermis stratum spongiosum and a mild diffuse inflammatory cellularity were typical in histopathology of skin. A specific pathogen or aetiology was not identified. Prevalence and severity of skin lesions was greatest during late summer and autumn, with the highest prevalence being 95%. Atypical lesions seen in winter and spring were suggestive of clinical resolution. PSD holds important implications for both trout aquaculture and still water trout fisheries. This case definition will aid future diagnosis, help avoid confusion with other skin conditions and promote prompt and consistent reporting.     

Cortisol and testosterone accumulation in a low pH recirculating aquaculture system for rainbow trout (Oncorhynchus mykiss)

Steroids accumulate in recirculating aquaculture system (RAS), although explanatory factors for such accumulation are still poorly explored. This study investigated the effect of water exchange rate and pH in six replicated RAS on the concentration of the stress hormone cortisol in rainbow trout blood plasma and in the holding water and of the sex steroids testosterone, 11‐ketotestosterone (11‐KT) and 17,20β‐dihydroxypregn‐4‐en‐3‐one (17,20β‐P) over a 70‐day experimental period. Three combinations of water exchange rate and pH were used each treatment, with two replications: (i) high water exchange rate (±1700 L kg^?1 feed) and neutral pH (±7.3), (ii) low water exchange rate (±500 L kg^?1 feed) and neutral pH (±7.3) and (iii) low water exchange rate (±500 L kg^?1 feed) and low pH (±5.8). Plasma cortisol concentrations at day 70 were higher (24.4 ± 9.5 ng mL^?1) for fish kept at low pH when compared to fish kept at neutral pH (12.0 ± 0.1 and 8.7 ± 0.2 ng mL^?1). Water cortisol and testosterone concentrations at day 35 were higher at low pH than at neutral pH, whereas water 11‐KT and 17,20β‐P did not differ among treatments. At day 70, there were no significant differences between low and high pH. These results demonstrate that low pH contributes to increased plasma cortisol concentrations and to its accumulation in water, possibly indicating a stress response to low pH. The higher concentration of testosterone but not of the other sex hormones point to unspecified reproductive effects that need further investigation.     

冷藏和冰藏条件下虹鳟鱼鱼片品质变化研究

为了科学地了解虹鳟鱼(Oncorhynchus mykiss)鱼片贮藏过程中的品质变化规律,以建立高效的品质控制技术,研究了虹鳟鱼鱼片在冷藏(3±1)℃和冰藏(0±1)℃条件下挥发性盐基氮(TVB-N)、色泽、腺苷三磷酸(ATP)关联物、K值及菌落总数(TAC)等指标的变化,评价不同温度对虹鳟鱼片品质的影响。结果显示:虹鳟鱼片TVB-N的增长速度在冷藏条件下显著高于冰藏条件,冷藏至第9天为20.72 mg/100g,冰藏至第15天为25.76 mg/100g;冷藏至第6天TAC为7.40 lg cfu/g,冰藏至第12天TAC为8.27 lg cfu/g;与冰藏相比,冷藏条件下虹鳟鱼片K值较高;肌苷酸(IMP)含量分别在冷藏8 h(8.36μmol/g)和冰藏24 h(8.70μmol/g)达到最大值,即冷藏和冰藏虹鳟鱼片的最佳食用时间分别是宰杀后的8 h和24 h。结合各项指标变化,冷藏和冰藏虹鳟鱼片的货架期分别为6 d和12 d。     

Moderate stocking density does not influence the behavioural and physiological responses of rainbow trout (Oncorhynchus mykiss) in organic aquaculture

Welfare in farmed fish got particular attention during the last decades from both governmental and public sides. In aquaculture context, welfare concerns are mainly related to handling procedures, water quality and stoking densities. In Europe, authorities had to clarify the threshold limits of stocking densities to maintain fish good welfare, including for organics aquaculture through the EC regulation 710/2009. However, effects of stocking density on fish welfare are complex and sometimes contradictory. Moreover, there is a lack of knowledge about the impact of density on fish welfare in organic aquaculture. Thus, the aim of the study is to asses welfare state of rainbow trout (Oncorhynchus mykiss) at two initial stocking densities (low density, LD: 12 kg/m³ and high density, HD: 17 kg/m³) fed using organic feed by combining the monitoring of growth performances, behaviour (swimming activity) and physiological indicators (i.e. cortisol, glucose, lactate, hematocrit, red blood cellule count and lysozyme). At the end of experiment, the stocking density reached 21 kg/m³ and 30 kg/m³ for the LD and HD respectively. Overall, growth performances, swimming activity and level of physiological indicators of stress and welfare were similar between HD and LD over the experiment duration. To conclude, we observed no alteration of fish welfare between the two stocking densities monitored. This study suggests that a final stocking density of 30 kg/m³ can be considered for organic aquaculture of rainbow trout respecting welfare.     

Metabolism of exogenous histamine in rainbow trout (Oncorhynchus mykiss)

Information on the metabolism of exogenous histamine in fish is of much concern regarding the effect of dietary histamine on fish. Histamine catabolic enzymes, diamine oxidase and histamine N-methyl transferase were measured in the tissues of rainbow trout. Diamine oxidase was detected in the stomach, pylorus caeca and intestine. Histamine N-methyl transferase was detected only in the liver.A change in the contents of histamine and its metabolites was observed in the tissues of rainbow trout after oral administration of histamine. A large amount of imidazole acetic acid was observed in the serum, kidney, liver and muscle. On the other hand, 1-methyl histamine was detected only in the liver. Histamine and its metabolites, imidazole acetic acid and 1-methyl histamine were metabolized and diminished within 48 hr in all tissues.These results showed that histamine was metabolized by two metabolic routes in rainbow trout. One is the main pathway producing imidazole acetic acid by intestinal diamine oxidase and the other is the complementary pathway producing 1-methyl histamine by liver N-methyl-transferase.     

Covariation between diploid and triploid progenies from common breeders in rainbow trout, Oncorhynchus mykiss (Walbaum)

The covariation between diploid and triploid progenies from common breeders was investigated in various progeny-testing experiments where either dams or sires were sampled from rainbow trout, Oncorhynchus mykiss (Walbaum), stocks. Triploidiza tion was found to frequently reduce the performance in the traits studied: body length and weight, growth, coefficient of condition and pyloric caeca number. Triploidization also generated significant interactions with the parental breeding value. These interactions were caused in part by the familial variance not being the same in triploids as in diploids, but also by actual ranking differences between diploid and triploid familial performances. However, the effect of these interactions was minor as compared with the amount of variation common to both ploidy levels (genetic correlations averaged 0.7–0.9). Therefore, selection of diploid breeders appeared efficient enough for improving triploid progeny, unless family selection methods including triploid progeny testing were preferred for other reasons. Lastly, it was observed that variances from maternal origin tended to be larger in triploids, whereas variances from paternal origin tended to be smaller, as compared with diploids. This point was discussed referring to the genetic make-up of triploids and in the scope of dams and sires for selective breeding.     

Evaluating the microbial effects of stocking freshwater snails (Physa gyrina) in water reuse systems culturing rainbow trout (Oncorhynchus mykiss)

A study was conducted to analyze the effects of snails (Physa gyrina) on biofilm, bacterial abundance, off-flavor-producing bacteria, and off-flavor compounds in reuse aquaculture systems culturing rainbow trout (Oncorhynchus mykiss). Eight experimental-scale systems were used, including four with and without snails. Mean heterotrophic bacteria counts in water were lower (P < 0.05) in systems with snails. Submerged surfaces of sumps containing snails were nearly biofilm-free, while sumps without snails were coated with biofilm. Geosmin levels in trout fillets from snail-stocked systems were generally lower but not statistically different from the controls. Rainbow trout health and performance was not affected by snail presence.     

Exploring the microbial diversity of the distal intestinal lumen and mucosa of farmed rainbow trout Oncorhynchus mykiss (Walbaum) using next generation sequencing (NGS)

In this study, next generation sequencing (NGS) was used to survey the 16S rRNA ribotypes of the distal intestinal lumen and mucosal epithelium of farmed rainbow trout. This approach yielded a library consisting of 2 979 715 quality filtered paired sequences, assigned to genus level of taxonomy using the Ribosomal Database Project (RDP). A high level of diversity was observed in both regions. A total of 90 bacterial genera were identified in the lumen of all fish sampled, compared with 159 in the mucosa. The allochthonous microflora was dominated by sequences belonging to the γ Proteobacteria (mean sequence abundance 54.3%), in particular the Enterobacteriaceae, with Yersinia, Serratia, Hafnia and Obesumbacterium the most abundant genera. Fewer γ Proteobacteria (mean sequence abundance 37%) were present in the mucosa, and autochthonous communities consisted of a more even split among the bacterial classes, with increases in sequences assigned to members of the β Proteobacteria (mean sequence abundance 18.4%) and Bacilli (mean sequence abundance 16.8%). The principal bacterial genera recorded in the mucosa were Cetobacterium, Yersinia, Ralstonia, Hafnia and Carnobacterium. The results of this study demonstrate that the luminal and mucosal bacterial communities may be different in their respective structures, and that the mucosal microflora of rainbow trout may be more diverse than previous research has suggested. This research also demonstrated a degree of conservation of bacterial genera between individual fish sampled, and is to the author's knowledge the first time the MiSeq^® NGS platform has been used to explore the rainbow trout intestinal microflora.     

Identification of a novel gill-specific calpain from rainbow trout (Oncorhynchus mykiss)

Calpains are calcium-dependent neutral proteases responsible for many cellular functions. The two forms of calpain ubiquitously expressed in mammalian tissues are known as μ-calpain and m-calpain. We report here the identification of a novel calpain that is similar to but distinct from the μ- and m-calpains in rainbow trout. The cDNA of the novel gene is 2623 bp in length with a single open reading frame. The predicted protein (676 amino acids) contains the conserved calpain characteristic domains that include: domain I (pro peptide), II (cysteine catalytic site), III (electrostatic switch), and IV (calmodulin-like) with five Ca²⁺-binding EF hands. Northern blot and RT-PCR analyses demonstrated that the novel calpain gene is predominantly expressed in rainbow trout gills. Comparison of the novel protein with the ubiquitously expressed calpains and several mammalian tissue-specific calpains revealed that the novel calpain is an orthologue of the mammalian digestive tract specific calpain (calpain 9).     

Bacterial pathogens in rainbow trout, Oncorhynchus mykiss (Walbaum), reared at Danish freshwater farms

During a 2-year period, bacterial fish pathogens were monitored on five rainbow trout, Oncorhynchus mykiss (Walbaum), freshwater farms in Denmark. A total of 1206 fish were examined and 361 bacterial isolates were identified phenotypically. Enteric redmouth disease, furunculosis and rainbow trout fry syndrome/coldwater disease were recorded. Infections caused by Flavobacterium psychrophilum occurred most frequently, but only one outbreak of enteric redmouth disease caused by Yersinia ruckeri serotype O1 and one of furunculosis caused by Aeromonas salmonicida were recorded during the monitoring period. Flavobacterium psychrophilum was isolated on all farms, both during disease outbreaks and from fish without any signs of disease. Serological investigations of F. psychrophilum showed that serotype Th was the dominant serotype found. The serotypes Th and Fd were involved in disease outbreaks of fry and larger fish. All isolates of F. psychrophilum showed proteolytic activities; however, a few isolates, belonging to serotype FpT did not degrade elastin and were not associated with mortality. Increasing resistance problems to oxytetracycline were demonstrated. More than half of the F. psychrophilum isolates showed resistance to oxolinic acid and oxytetracycline. No antibiotic resistant isolates were found among Y. ruckeri and A. salmonicida .     

Cholesterolaemia and triacylglycerolaemia in farmed rainbow trout,Oncorhynchus mykiss

Physiological (reference) value intervals determined by the lower 2.5% and upper 97.5% quantiles were calculated for blood plasma cholesterol (CHOL) and triacylglycerol (TGL) in farmed rainbow trout, Oncorhynchus mykiss, in raceway culture. The fish were given dry pelleted diets that contained 37–47% crude protein and 7–14% crude fat and were kept at a stocking density of 50 kg m^?3 in tanks provided with running freshwater at an ambient temperature of 3–16°C and dissolved oxygen, 8.4–11.5 mg L^?1. Blood was sampled between September and November at a photoperiod of 9:00–13:00 hours: 11:00–15:00 hours (light:dark). Cholesterol levels were significantly (P = 0.0001) greater in males (4.7–12.1 mmol L^?1, n = 34, mean weight 406 ± 138 g) than immature females (3.2–9.7 mmol L^?1, n = 386, mean weight 416 ± 147 g). Physiological range for TGL in immature females and males was 2.4–14.4 mmol L^?1 (n = 249, mean weight 418 ± 149 g). The distribution and density of the quantiles in the tested reference group were made possible by the use of histograms, which showed normal distributions for CHOL in males and in females, but not for TGL, in which a sinistral asymmetry was found. Correlation and regression analyses indicated significant (P = 0.0000) dependence between the CHOL and total protein (r² = 76.2%), CHOL and Fulton's condition factor (r² = 43.3%) and CHOL and absolute weight of liver (r² = 45.5%). Fluctuation in cholesterolaemia and triacylglycerolaemia, depending on nutrition and the aquaculture method is discussed below.     

Interaction between diet and genetic aptitude for weight and growth in juvenile rainbow trout, Oncorhynchus mykiss (Walbaum)

Samples of rainbow trout, Oncorhynchus mykiss (Walbaum) alevins from 17 independent families (full‐sib‐groups) were raised from the start of feeding until the age of 18 weeks post‐hatching with three diets (C, G and S) differing in protein content (fish soluble protein concentrate: 84% in C, 54% in G and 44% in S) and carbohydrates (none in C, 30% glucose in G and 40% crude corn starch in S). Fish were fed to near satiation, and their body weight and growth were measured. Diet effect was highly significant (G< C < S), as well as the familial effect. The major part of the familial variance (80–90%) was common to the three diets. However, a minor part of the familial variance was observed to be diet dependent (family × diet interaction), and was found to result mainly from relative performances with carbohydrates (G and S diets) vs. pure protein (C diet). These results indicate that genetic improvement of growth should suffer little impairment from possible changes in future feed formulations.     

虾青素在虹鳟体内的沉积与降解研究

为研究着色虹鳟在摄食状态和饥饿状态下的虾青素降解规律,实验选用平均体质量为(101.9±1.3)g的未着色虹鳟和已着色虹鳟,对未着色虹鳟饲喂含虾青素(100 mg/kg)饲料以研究虾青素在机体的沉积规律(虾青素沉积组);对着色虹鳟,饲喂含虾青素(100 mg/kg)饲料(正对照)、不含虾青素饲料(摄食降解组)或予以饥饿处理(饥饿降解组),实验共设4个处理组,每个处理组3个重复.实验共持续4周,每周采样一次,测定肌肉、肝脏和全鱼虾青素含量,血清类胡萝卜素含量,肌肉色差值(L*,a*,b*)和肌肉罗氏比色卡得分.结果表明,虾青素沉积组的虹鳟肌肉、肝脏虾青素含量、肌肉红度值和罗氏比色卡得分随饲养时间延长而增加(P＜0.05),在第3周时达到基本稳定,与第4周测定值无显著差异(P＞0.05);在4周养殖期内,全鱼虾青素含量呈增加趋势,而全鱼虾青素沉积率则呈下降趋势,第1周、第4周时的全鱼虾青素含量和全鱼虾青素沉积率分别为3.71 mg/kg、8.59 mg/kg和21.31％、15.26％;饥饿降解组和摄食降解组虹鳟的全鱼、肌肉、肝脏虾青素含量、肌肉红度值和罗氏比色卡得分随养殖时间延长逐渐降低(P＜0.05),其中饥饿降解组的下降趋势更为明显,第3周后,这种降低趋势减缓.上述研究表明,在虹鳟饲料中添加100 mg/kg虾青素,经过3周饲养即可使肌肉达到着色要求,虾青素的沉积率随时间延长而下降;饥饿和投喂不含虾青素的饲料均可使已着色虹鳟肌肉虾青素含量和红色度显著下降,饥饿使虾青素的减少更加迅速,虾青素在鱼体内的减少量随时间的延长而降低.