Movement patterns of seaward migrating European eel (Anguilla anguilla) at a complex of riverine barriers: implications for conservation

River infrastructure such as weirs and hydropower stations commonly present migrating fish with multiple potential passage routes. Knowledge of the cues fish use to navigate such environments is required to protect migrants from hazardous areas and guide them towards safe passage; however, this is currently lacking for many species. Employing high‐resolution positioning telemetry, this study examined movements of downstream migrating adult European eel, Anguilla anguilla, as they encountered a complex of water control structures in one location on the River Stour, southern England. The distribution of eels across five potential routes of passage differed from that predicted based on proportion of discharge alone. Certain routes were consistently avoided, even when the majority of flow passed through them. Passage distribution was partially explained by avoidance in the vicinity of a floating debris boom. Movement paths were nonrandomly distributed across the forebay and eels moved predominantly within a zone 2–4 m from the channel walls. Understanding of avoidance and structure oriented movementation exhibited by eels will help advance effective guidance and downstream passage solutions for adults.     

Seasonal Changes in Rigor Development and Flesh Texture of Wild Japanese Sea Bass (Lateolabrax japonicus)

The season for finding the firmest sashimi made from wild Japanese sea bass was investigated. Flesh rigor tension and contraction were measured by a “new” device with isometric (muscle length kept constant) and isotonic (balance beam moves freely) transducers. Both flesh rigor tension and contraction peaks appeared at the same postmortem times, with attainment of ultimate pH and adenosine triphosphate/inosine monophosphate ratio in four seasons. Seasonal seawater temperature correlated negatively to seasonal maximum rigor contraction and positively to seasonal flesh breaking strength at 72 h postmortem. After rigor peak tension attainment, the tension relaxation was much lower than that of other wild fish species, especially in summer. The sea bass muscle resisted structure disruption in rigor isometric tension generation. Wild sea bass sashimi was firmest in breaking strength in summer.     

蛋白酶解对鲣鱼肉乳化特性的改善

天然鱼蛋白乳化性不佳,难以满足实际生产需求,但鱼蛋白的酶解改性可改善其功能特性,并拓展应用范围。以鲣鱼白色肉为原料,以水解度和乳化性为主要指标,比较了不同蛋白酶(胰蛋白酶、风味蛋白酶、木瓜蛋白酶)和水解时间对酶解液制备和鱼蛋白乳化性的影响,优化了酶解工艺参数。将鱼蛋白进行冷冻干燥后,分析鱼蛋白酶解前后溶解性、乳化性和起泡性等功能特性的差异。结果表明,当胰蛋白酶添加量2 000 U·g^-1,酶解10 min时,鱼蛋白水解度(DH)达到8.2%,此时鱼蛋白乳化特性最佳。与酶解前样品相比,酶解后鱼蛋白的乳化活性和乳化稳定性显著提高,其溶解度、起泡性和起泡稳定性均有一定程度的改善。酶解制备的鲣鱼蛋白在广泛pH范围内具有更好的功能性质,在食品工业具有更高的应用价值。     

Winter monsoon promotes the transport of Japanese temperate bass Lateolabrax japonicus eggs and larvae toward the innermost part of Tango Bay,the Sea of Japan

Northwesterly cold winds characteristic of the East Asian Winter Monsoon (EAWM) dictate winter climatic conditions over the Japanese Archipelago. Japanese temperate bass Lateolabrax japonicus is a commercially important coastal fish that spawns offshore in winter and uses shallow waters as nursery habitats. To investigate the effects of EAWM on the planktonic period of L. japonicus, eggs, larvae, and juveniles were quantitatively collected in Tango Bay on the Sea of Japan side in winter and spring from 2007 to 2017. Although eggs occurred close to the mouth of the bay, planktonic larvae occurred further inside as they developed. The horizontal distribution of planktonic larvae, combined with water velocity data obtained from mooring observations, indicated that planktonic larvae are transported south‐ to westward through Ekman current and an anticyclonic circulation, which are driven by northwesterly winds. To evaluate survival during the planktonic period in each year class, the abundance of benthic larvae/juveniles was divided by winter total landings of Lateolabrax spp. (proxy of the spawning stock size). This survival index exhibited a positive correlation with the northwesterly component of winter winds, and a negative correlation with winter air temperature (average from December to February, Spearman's correlation, p < .05). There was, however, no significant correlation with winter water temperature or winter freshwater discharge in the bay. We conclude that northwesterly cold winds of EAWM play a critical role in transporting L. japonicus eggs and larvae toward nursery habitats, specifically beaches and estuaries fringing the innermost part of Tango Bay.     

Dietary taurine impacts the growth,amino acid profile and resistance against heat stress of tiger puffer (Takifugu rubripes)

A 56‐day feeding trail was conducted to evaluate the effects of taurine (Tau) supplementation on growth performance, amino acid profile and heat stress resistance capacity in juvenile Takifugu rubripes (initial body weight: 32.28 ± 0.20 g). Tiger puffer were distributed into five groups and each received one of the following diets: each diet was supplemented with 0 (T1), 5 (T2), 10 (T3), 20 (T4) or 50 (T5) g Tau/kg, respectively. Growth performances were significantly ameliorated with fed diet T3 (p < .05). The Tau content of muscle increased significantly as dietary Tau increased (p < .05). Compared to the control group, fish fed diets T4 and T5 showed significantly higher concentration of triglyceride and urea, respectively (p < .05), while taurine transporter (TauT) gene and IGF‐1 gene expression increased significantly in fish fed diets T3 and T4, respectively (p < .05). After acute heat stress, HSP70 gene expression levels were significantly greater in the livers and spleens of T. rubripes (p < .05) fed diet supplemented with Tau. Levels of complement C4 were highest in fish fed 10 g/kg Tau (p < .05). These data suggested that dietary supplemented with taurine indicated positive effects on growth performances, amino acid profile and resistance against heat stress for T. rubripes.     

Anabolism,catabolism and proteomic analysis in the slow‐twitch muscle of pacu (Piaractus mesopotamicus) submitted to prolonged fasting followed by refeeding

Here, we aimed to study the slow muscle of the fish Piaractus mesopotamicus submitted to 30 days of fasting (D30) followed by 1 day (D31) or 30 days of refeeding (D60). Histological analysis of fibre diameter was performed in D30 and D60. The gene expression of parvalbumin (pvalb), atrogenes (murf1a, murf1b, mafbx) and anabolic genes (igf‐1, mtor) was analysed using RT‐qPCR in D30, D31 and D60. The proteome was obtained by shotgun proteomics at D30 and D60, and the set of differentially expressed proteins was analysed by bioinformatics. In all experiments, the control was regularly fed fish. The histological analysis showed no changes in muscle fibre diameter. The expression of catabolic and anabolic genes was not changed, except for the downregulation of igf‐1 in D30 and of mafbx in D31. The expression of pvalb was not changed in D30 and D60 but was decreased in D31. The proteomic analysis identified 169 proteins in D30 (24 upregulated and 18 downregulated) and 170 proteins in D60 (17 upregulated and 21 downregulated); many of them were related to energetic metabolism and intracellular Ca²⁺ homoeostasis. Overall, our results indicate that the slow‐twitch muscle presented few changes upon prolonged fasting and refeeding condition.     

Availability of potato protein concentrate as an alternative protein source to fish meal in greater amberjack (Seriola dumerili) diets

Potato protein concentrate (PPC) is a promising candidate as a fish meal (FM) substitute because it has high protein and essential amino acid content. In the present study, we replaced FM in greater amberjack diets with PPC to investigate the effect on growth and feed utilization. Four isonitrogenous, isolipidic and isocaloric experimental diets were prepared by substituting 0, 20, 40 and 60% of FM protein with PPC (Control, P20, P40 and P60 respectively). The in vitro protein digestibility of protein in PPC was 88.8%, relative to 100% protein in the FM. The in vitro protein digestibility of protein in the experimental diets also decreased with increasing PPC and was lowest at 84.2% in P60. After the 7‐week feeding trial, final body weight, weight gain and thermal growth coefficient tended to decrease with increasing PPC and were significantly lower in P60 than in the control (p < .05). Further, fish fed with diets P40 and P60 showed significantly lower feed conversion and protein efficiency ratios than the control group (p < .05). In conclusion, the results suggest that PPC can replace up to 20% of FM in the diet of greater amberjack without compromising the growth performance or feed efficiency.     

Effect of Dimethyl sulfoxide (DMSO) and egg yolk on sperm motility,fertility and hatching rates of depik Rasbora tawarensis (Pisces: Cyprinidae) eggs after short‐term cryopreservation

Cryoprotectant is the crucial factor in the cryopreservation process. In general, there are two types of cryoprotectant, permeating and non‐permeating cryoprotectants. Dimethyl sulfoxide (DMSO) and egg yolk are common permeating and non‐permeating cryoprotectants respectively. Hence, the objective of the present study was to determine the best proportion of DMSO and egg yolk for the cryopreservation of Rasbora tawarensis sperm. A completely randomized experimental design was used in this study which involves two types of cryoprotectant and their combination at different concentrations, namely 5% DMSO, 5% egg yolk, 5% DMSO + 5% egg yolk and 2.5% DMSO + 2.5% egg yolk. Every treatment was conducted in three replicates. Combination of 5% DMSO + 5% egg yolk gave the best results cryoprotectant treatment had significant effects on sperm motility, fertilization and hatching rate of the R. tawarensis eggs (p < .05). It is concluded that the best proportion of cryoprotectants for sperm cryopreservation in this species is 5% DMSO + 5% egg yolk.     

Effect of fish meal replacement with Carinata Brassica carinata in low animal protein diets of rainbow trout Oncorhynchus mykiss (Walbaum) on trypsin activity,protein and amino acid digestibility and bioavailability

Replacement of >25% of fish meal (FM) with aerobically converted carinata meal (ACCM) in low (200g/kg) animal protein (reference = 200g/kg FM) diets of rainbow trout Oncorhynchus mykiss resulted in reduced growth, partly due to reduced feed consumption and protein utilization. In this study, we determined the effect of FM replacement with ACCM on trypsin activity, apparent digestibility coefficients (ADCs) of protein, and essential amino acid (EAA) or conditionally essential amino acid (CEAA) ADCs and bioavailability. Replacement of FM did not alter protein ADCs or trypsin activity. Replacement of >25% FM reduced all EAA and CEAA ADCs except for arginine and leucine which were only reduced by 75% FM replacement. Only serum free lysine and muscle free histidine were reduced by >25% FM replacement. Muscle free lysine was only reduced by 75% FM replacement. Replacement of FM reduced EAA peak concentrations and resulted in slower release of EAAs in serum. Cumulative total EAAs in serum and muscle decreased with FM replacement. Ratios of EAAs to lysine showed that tryptophan was the most limiting EAA. However, isoleucine, leucine, methionine and phenylalanine were also inadequate for muscle synthesis for the first 9–12 hr following force‐feeding. Optimal time for protein synthesis was ≥36 hr. Although any level of FM replacement did not reduce protein ADCs and trypsin activity, replacement of ≥25% FM reduced EAA ADCs and bioavailability of lysine and histidine, which partly contributed to the observed differences in growth.     

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.