Turbid water induces refuge behaviour of a commercially important ayu: A field experiment for interstream movement using multiple artificial streams

Riverine systems are inherently dendritic in nature, and turbid water may not necessarily flow equally throughout an entire catchment. Tributaries have the potential to serve as refugia from temporarily turbid water in the main stem. As ayu (Plecoglossus altivelis) are one of the important species for the inland fisheries industry and recreational fishing, their behaviour in a branched river network is a primary concern. We released ayu with radio‐transmitting tags into two experimental streams that joined at a downstream pool. Turbid water was released into one of the streams, and we identified whether avoidance movement of ayu between the two experimental streams was triggered by flowing turbid water. The suspended solid concentration elevated rapidly after adding the turbid water and was maintained at more than 400 mg/L for 3 hr. Avoidance movement of ayu was triggered when the suspended solid concentration exceeded approximately 200 mg/L. Then, most ayu moved from the turbid stream to the nonturbid one, leading to a difference in ayu density between the two streams. Therefore, we demonstrated that turbid water induced interstream movement of a commercially important ayu as refuge behaviour, suggesting that river connectivity is important for the persistence of the ayu.     

Spatial and seasonal variations of radiocesium concentrations in an algae-grazing annual fish,ayu Plecoglossus altivelis collected from Fukushima Prefecture in 2014

Fisheries Science - To elucidate spatial and seasonal variations of radiocesium (134Cs and 137Cs) concentrations in ayu Plecoglossus altivelis, amphidromous fish samples were collected both from...     

Spatiotemporal distribution of Flavobacterium psychrophilum and ayu Plecoglossus altivelis in rivers revealed by environmental DNA analysis

Outbreaks of bacterial cold-water disease (BCWD), caused by Flavobacterium psychrophilum, are widespread in Japan, especially among ayu Plecoglossus altivelis. There are few investigations of F. psychrophilum in river water, and its seasonal distribution has not been clarified. We aimed to identify the spatiotemporal dynamics of F. psychrophilum and ayu to provide information that is useful for establishing a countermeasure for BCWD. Quantitative analysis of environmental DNA (eDNA) was used to clarify the year-round dynamics of ayu and F. psychrophilum. We sampled river water from the Nagara and Ibi rivers in Japan, and conducted monthly water sampling and eDNA quantification. Changes in the eDNA concentration of ayu were consistent with the known life histories of the fish. There was a strong negative correlation between the eDNA concentration of F. psychrophilum and water temperature, suggesting a strong dependence of F. psychrophilum dynamics in the river on water temperature. Furthermore, relatively high eDNA concentrations were recorded for both organisms in early summer and fall, suggesting that ayu is infected with F. psychrophilum during these seasons when experiencing up- and downmigration, respectively.

     

Accumulation flux of nitrogen in mudflats and its implications for benthic shellfish culture

In order to evaluate impacts of benthic shellfish culture on sediments in the Daguhe Estuary, surface sediments are sampled in February, May, August and November 2009 and the water content and nitrogen content of sediment, accumulation flux of nitrogen are studied. About 40 % of the mudflat in the estuary is used for bottom sowing culture for Manila clam Ruditapes philippinarum. The seeding density is 1.1–1.5 kg m^?2 in the estuary if the mean weight of juvenile clam is 0.3–0.5 g. Moreover, the stock density of cultivated clam that can be harvested (with mean weight 8 g) is 450–1,600 individual m^?2, and the annual yield of this species of clam is about 3.4 kg m^?2. There is significant spatial difference of water content of sediment from February to November, during which the water content in the uncultured mudflat, the cultured mudflat and the river way is 32.07, 43.95 and 37.69 %, respectively. There is no significant spatial difference of TN (total nitrogen) content of sediment, and the TN content in the cultured mudflat, the uncultured mudflat and the river way is 0.26, 0.22 and 0.29 mg g^?1, respectively. Moreover, the IN (inorganic nitrogen) content of sediment in the cultured mudflat, the uncultured mudflat and the river way is 0.09, 0.08 and 0.14 mg g^?1, which implies that there is no significant spatial difference of IN content. Furthermore, there is no significant spatial difference of EN (exchangeable nitrogen) content of sediment from February to November, during which the EN content in the uncultured mudflat or the river way is about 0.04 μg g^?1 and it is 0.03 μg g^?1 in the cultured mudflat. Thus, the benthic shellfish culture may increase the water content and there is no significant effect of benthic shellfish culture on nitrogen content. The accumulation flux of TN in the cultured mudflat, the uncultured mudflat and the river way is 0.94, 1.13 and 1.40 mg cm^?2 year^?1. The accumulation flux of IN in the cultured mudflat, the uncultured mudflat and the river way is 0.31, 0.39 and 0.66 mg cm^?2 year^?1. Moreover, the accumulation flux of EN in the uncultured mudflat and the river way is nearly equal, which is 0.21 and 0.20 μg cm^?2 year^?1, respectively. The accumulation flux of EN in the cultured mudflat is 0.10 μg cm^?2 year^?1. Thus, the benthic shellfish culture in the estuary does not enhance the accumulation of TN or IN. Nevertheless, it may reduce the accumulation of EN. Furthermore, it is cautious to evaluate the effect of benthic shellfish culture on sediments by the nitrogen content only. The accumulation flux of nitrogen may be one better index to evaluate the impact.     

The effects of bioturbation by the Venus clam Cyclina sinensis on the fluxes of nutrients across the sediment–water interface in aquaculture ponds

A mesocosm experiment was conducted to study the effects of bioturbation by the marine bivalve Cyclina sinensis in an aquatic system and to examine how the bioactivities of this clam alter the rate at which nutrients are exchanged across the sediment–water interface. A dark incubation experiment was performed to determine the fluxes of inorganic nutrients (NH₄ ⁺, NO₃ ^? + NO₂ ^? and PO₄ ^3?), benthic chlorophyll a (Chl a), organic matter and sediment oxygen consumption (SOC) on days 1, 10, 20 and 30. C. sinensis destroyed the initial sediment surface and partially enhanced oxygen penetration into the sediment. The clam also increased the water content and volume of the oxic sediment. The analysis showed that increases in the clam density and time period produced higher fluxes of all the nutrients (NH₄ ⁺, NO₃ ^? + NO₂ ^? and PO₄ ^3?) in the bioturbated chambers compared with the control (non-bioturbated chambers). The concentration of Chl a in the sediment increased significantly at the end of the experiment (day 30) (p < 0.05). The SOC rate increased significantly with the increase in density and with the time period from day 10 to day 30 (p < 0.05). As a result, the fluxes of nutrients increased with increased SOC, producing oxygen-induced sediment mineralization. Our findings suggest that the activities of the clams could positively influence SOC and cause an increase in the fluxes of inorganic nutrients. These effects may substantially improve the primary productivity and water quality of earthen pond ecosystems.     

Demographic survey of the yellow-phase Japanese eel Anguilla japonica in Japan

Catch statistics and biological data of the Japanese eel Anguilla japonica from 12 river systems in nine prefectures of Japan (36°N, 140°E–31°N, 130°E) during 1999–2004 were analyzed in order to evaluate the demography of A. japonica in Japan. Significant differences in biological characteristics of 6388 eels were found among the river systems. Fishery catches of eels in all locations have declined, but the magnitudes or patterns of decline seem to be different. Of sex-identified eels, mean total lengths ± SD (mm) of females (n = 3776) and males (n = 962) were 495.6 ± 104.3 and 412.9 ± 80.7, respectively, and overall sex ratio (% female) was 79.6 %. Mean age (years) and growth rate (mm year^?1) were 5.0 ± 1.9 and 96.7 ± 38.6 for females (n = 3643) and 3.6 ± 1.7 and 120.5 ± 65.4 for males (n = 907), respectively. This study highlights the demographic heterogeneity of the A. japonica among the studied river systems, which suggests that it is important to conserve a variety of habitats in multiple river systems as an inclusive management target in addition to restoration of the diversity of habitats for eels in a single river system.     

Mercury and methyl mercury concentration in sediment,benthic, Barbus Grypus and pelagic,Barbus esocinus fish species,from Musa estuary,Iran

The concentrations of mercury (Hg) and methyl mercury (MeHg) in sediment and tissues of Barbus grypus and Barbus esocinus fish species from Musa estuary, north part of the Persian Gulf, were measured. The order of Hg and MeHg concentrations in the sediment and tissues of the fish species was as follows: liver > gill > muscle > sediment. In the tissues of two fish species, the Hg and MeHg concentrations were highest in liver whereas lowest in the muscle. In the sediment, mean concentrations of Hg and MeHg were 0.83 and 0.437 µg g^?1. Mean concentrations of Hg and MeHg in B. grypus were 1.2–0.624 µg g^?1 and in all tissues of B. esocinus were 0.75 and 0.421 µg g^?1. Significant correlation between heavy metal concentration in sediment and fish may be related to high variability of heavy metal in the sediment.     

Experimental analysis on the relationship between the population density of ayu Plecoglossus altivelis altivelis and fishery catch by “Tomozuri” angling

To investigate the relationship between the population density of ayu and the survival rate, number of ayu caught by “Tomozuri” angling and total fishery catch, ayu were introduced into experimental ponds with currents at densities of 1.1–6.1/m² in 2011 and 2012. After stocking in May, fishing was conducted from early July to late August or early September. The proportion of dead ayu in each pond was less than 20 % through the experiment and was not correlated with the initial density of ayu in either year. The growth rates of ayu that were fished and that remained in ponds to the end of the experiment were negatively correlated with the initial density. However, the number and catch of ayu fished by Tomozuri peaked at an initial density of 2.6–4.7/m². Medium- and large-sized ayu heavier than 30 and 50 g, respectively, caught by fishing peaked at initial densities of 2.6/m² and 2.1–2.6/m². These results suggest that the traditional criterion on the stock density of ayu, 0.6–0.7/m², is too low from the viewpoint of Tomozuri angling, and recent stock densities used in many prefectures, 0.5–2.0/m², are not sufficient.     

Development of phytoplankton communities and common off-flavors in a biofloc technology system used for the culture of channel catfish (Ictalurus punctatus)

The use of biofloc technology production systems continues to increase in the aquaculture industry worldwide. Recent research demonstrated that outdoor biofloc systems can be used to produce high yields of channel catfish (Ictalurus punctatus). However, studies have not yet been performed to determine the development and composition of phytoplankton communities and related off-flavor problems in these biofloc production systems. In this study, water samples were collected biweekly from May to November and channel catfish samples were collected during harvest in November from nine 18.6 m² biofloc culture tanks. Water and fillet samples were analyzed for levels of the common off-flavor compounds geosmin and 2-methylisoborneol (MIB). The development and composition of phytoplankton communities in each culture tank was also monitored. In addition, water and biofloc samples were evaluated to assess the microbial sources of geosmin and MIB within the culture tanks. Phytoplankton (including algae and cyanobacteria attached to bioflocs) biomass, as determined by concentrations of chlorophyll a in the water, gradually increased in all tanks over time. Phytoplankton communities that developed in the culture tanks were dominated by fast-growing, unicellular and small colonial types of green algae (chlorophytes) and diatoms (bacillariophytes) and slower growing, small colonial types of cyanobacteria (cyanophytes). A positive correlation (p < 0.05) between cumulative feed addition and chlorophyll a concentration was found. Although geosmin and MIB were present in the culture water of each tank during most of the study, levels were typically low and only one tank yielded catfish with geosmin and MIB in their flesh at levels high enough to be designated as off-flavor. A positive correlation (p < 0.05) between cumulative feed addition and MIB concentrations in the water of culture tanks indicates a greater potential for MIB-related off-flavor problems at high feed application rates. The microbial sources responsible for production of geosmin and MIB in the culture tanks remain unknown.     

Changes in oocyte and blood plasma osmotic components of ayu, Plecoglossus altivelis Temminck & Schlegel during oocyte maturation

Oocyte maturation in teleosts is characterized by a complex series of cytoplasmic and nuclear changes. The purpose of this study is to present sequential changes in the oocyte constituents and regulatory mechanisms involved in the hydration and osmotic regulation of oocytes during final maturation of ayu, Plecoglossus altivelis Temminck & Schlegel. Oocyte volumes and water contents in ayu (P. altivelis) markedly increased from 0.372 mm³ and 60.5% at the mature stage to 0.712 mm³ and 79.4% at the time of oviposition. In the same period, net increases in total free amino acids and electrolytes were noted, and involvements of these constituents in the water uptake by oocytes are discussed. Moderate oocyte hydration in ayu is accompanied by steady increases in Na⁺, but not K⁺, and these observations are in contrast to results for all other marine teleosts reported elsewhere. In the present study, a steady increase in oocyte Na⁺ during maturation until ovulation pre‐dominantly results from diffusional leakage due to concentration gradients, while at the time of oviposition, both active transport and diffusional pathways play important roles in osmotic regulation in ayu oocytes.     

Combined influence of water temperature, salinity and body size on energy budget in the sea cucumber Apostichopus japonicus Selenka

The worldwide demand for sea cucumber is outpacing the sustainable harvest capabilities of fisheries. Sea cucumber ranches and farms are striving to supplement wild harvest, but variable temperature and salinity conditions in pond culture systems make sea cucumber production challenging. In this study, we evaluated how water temperature, salinity and body size affected the energy budget of pond-cultured sea cucumber Apostichopus japonicus Selenka. An orthogonal design was used to identify the most suitable conditions for energy consumption and scope for growth (SFG). After the 42-day experimental period, we found that water temperature, salinity and body size significantly influenced energy consumption, while salinity and body size were the main influencing factors on SFG. Based on these results, we suggest that a water temperature of 16 °C and a salinity of 30 g L^?1 are optimal conditions for stocking sea cucumber A. japonicus with a body size of 37.34 ± 4.63 g. As such, the optimum stocking seasons for sea cucumber A. japonicus may be April in the spring and October in the autumn.     

Microbial community in a multi-trophic aquaculture system of <Emphasis Type="Italic">Apostichopus japonicus</Emphasis>, <Emphasis Type="Italic">Styela clava</Emphasis> and microalgae

An integrated multi-trophic aquaculture (IMTA) system consisting of the ascidian Styela clava and the sea cucumber Apostichopus japonicus with microalgae was grown in a seawater mesocosm. Microbial populations in the water, sediment and shelters were monitored over time. The composition of the water microbial community in the IMTA system did not differ significantly from that of the traditional culture system without ascidians. Bacterial populations in the water, sediment and shelters were low in the traditional A. japonicus aquaculture system, and lower in the IMTA system. The number of Vibrios in the water, sediment and shelters in the IMTA system was significantly lower than in the traditional culture (p < 0.05), while the quantity of Bacillus was higher in the sediment and shelters. All of these results indicate that the IMTA system effectively inhibited the growth of harmful bacteria, an important positive function in the health of the culture. The bacterial diversity index in the water in the IMTA system was between those of the baited and non-baited traditional aquacultures and was slightly reduced in the shelters. Over time, the bacterial diversity index in the sediment gradually dropped, especially in summer and autumn, when it was significantly lower than in the traditional culture. In winter, the diversity index increased to some extent, approaching that of the traditional culture.     

The effect of dosing with sodium hydroxide (NaOH−) on water pH and growth of Haliotis midae in an abalone serial-use raceway

Abalone culture systems are characterised by high water exchange rates as abalone are sensitive to changes in water quality. To reduce the costs of pumping, serial reuse systems have been tested. As water pH can decline in these systems, this study determined the effect of raising pH through the addition of sodium hydroxide (NaOH^?) on weight gain, length gain and feed conversion ratio of H. midae in a serial-use raceway. Dosing with NaOH^? increased pH by 0.3, 0.27 and 0.21 units at positions 1, 2 and 3 of a serial-pass system, respectively. Weight gain (Wg) and length gain (Lg) were correlated with pH (Wg: F _{1, 16} = 16.35, P = 0.0009, r ² = 0.51; Lg: F _{1, 16} = 16.16, P = 0.0009, r ² = 0.50), and using pH, dissolved oxygen and free ammonia nitrogen as independent variables suggested that water pH was the best predictor for abalone growth.     

贵定王寨河浮游藻类调查及水质评价

对贵定野生大鲵自然生态保护区内王寨河6个断面不同季节浮游藻类的种类、密度进行了调查,并采用Margalef和Shannon-wiener多样性指数进行了水质评价.结果表明,王寨河春季有浮游藻类5门83种,秋季有4门66种.王寨河水质总体上清洁,有利于大鲵(Andrias davidianus)野生种群的栖息生存.     

Toxicity of the antifouling biocide Sea-Nine 211 to marine algae, crustacea, and a polychaete

We evaluated the acute toxicity of the antifouling biocide Sea-Nine 211 to the algae Chaetoceros calcitrans, Dunaliella tertiolecta, Tetraselmis tetrathele, and Skeletonema costatum, the crustacea Tigriopus japonicus and Portunus trituberculatus, and the polychaete Perinereis nuntia. The algae, and especially the diatoms C. calcitrans and S. costatum, were sensitive to Sea-Nine 211 toxicity, with the average acute toxicity values being 0.32, 3.9, 1.6, 0.22, 1.6, 12, and 27 μg/l for C. calcitrans, D. tertiolecta, T. tetrathele, S. costatum, T. japonicus, P. trituberculatus, and P. nuntia, respectively. A sediment toxicity test for Sea-Nine 211 using the polychaete P. nuntia revealed demonstrated that the 14-day median lethal concentration was 110 μg/kg dry-wt sediment and that growth was the most sensitive indicator. The chronic toxicity values of Sea-Nine 211 for the diatoms C. calcitrans and S. costatum were within the range of reported Sea-Nine 211 concentrations in seawater in coastal Japan, and the toxicity values for P. nuntia were within the reported concentrations in sediment. Based on these results, Sea-Nine 211 may have toxic effects on some sensitive species residing in the coastal areas of Japan, but the ecological risk posed by Sea-Nine 211 would appear to be confined to a limited area of Japanese coastal waters.     

Dietary ascorbic acid requirement of juvenile ayu (Plecoglossus altivelis)

To investigate dietary ascorbic acid (AA) requirement of juvenile ayu (Plecoglossus altivelis) weighing 1.27 ± 0.02 g, eight diets were formulated with graded levels (0, 20, 40, 80, 160, 320, 640 and 1280 mg AA kg^?1) of AA supplied as ascorbyl polyphosphate. Each experimental diet was fed to four‐replicate groups to apparent satiation three times a day for 8 weeks. At the end of the feeding trial, fish fed AA‐deficient diet showed visible AA deficiency signs and low survival. Based on the four‐parameter saturation kinetics model, the calculated AA requirement levels for each dose‐dependent response [weight gain, hepatic AA concentration, hydroxyproline (HyPro) concentration in skin and HyPro concentration in backbone] were 116, 226, 47 and 35 mg kg^?1, respectively. Based on the maximal growth performance, a level of 116 mg AA kg^?1 was recommended for commercial diet of juvenile ayu. To maintain tissue HyPro saturation and avoid AA deficiency symptoms, the minimum required dietary AA level was 47 mg kg^?1. Hepatic AA saturation was considered as the most stringent criterion for determination of AA requirement.     

Feeding territory and variations in behavioural modes of algae‐grazing fish Plecoglossus altivelis ryukyuensis (Ryukyu‐ayu) in subtropical island streams

Abstract – Social and foraging modes in fish often vary between individuals with different body sizes and between populations under different ecological conditions. We studied social and foraging behaviour of algae‐grazing fish Plecoglossus altivelis ryukyuensis (Ryukyu‐ayu) inhabiting Japanese subtropical island streams. Ryukyu‐ayu exhibited four behavioural modes: territorial, schooling, solitary and floating. Their body sizes differed among these modes. Territorial fish predominantly foraged on benthic algae, whereas schooling and solitary individuals frequently consumed drifting materials as well. Schooling fish were smaller than territorial fish, but, unlike some other algae‐grazing fish species, did not use schooling to gain access to food within territories. Territorial fish attacked smaller conspecifics but exhibited lateral display towards larger fish and schooling fish while occasionally attacking grazing gobies. Larger fish maintained larger feeding territories and occupied territories for longer periods than smaller fish did. This suggests that, in Ryukyu‐ayu, intra‐ and interspecific food competitions and relative body size can influence diverse behavioural modes and duration of territory occupation. We also found that Ryukyu‐ayu foraged more often and had larger feeding territories than ayu P. a. altivelis inhabiting temperate streams. We conclude that foraging strategies of Ryukyu‐ayu may have adapted to subtropical island streams, where algal productivity is much lower than that in temperate regions.     

The impact of Chinese mitten crab culture on water quality, sediment and the pelagic and macrobenthic community in the reclamation area of Guchenghu Lake

The effects of crab aquaculture on the water and sediment quality and the pelagic and macrobenthic community of the adjacent reclamation area of Guchenghu Lake, Jiangsu Province were evaluated over two consecutive crop cycles from April 2010 to November 2011. The results indicated that most of the nutrient concentrations in both the water column and the sediment varied temporally and showed significant spatial differences. The peak values of most of the physico-chemical parameters measured were obtained during the summer or autumn, whereas the opposite result was observed for suspended solids. A higher zooplankton density and lower phytoplankton biomass were observed in ponds than in other sampling sites, whereas Cyanophyta (80 %), with Planktothrix rubescens as the dominant taxon, was predominant in the canal closest to the ponds. The benthic community was dominated by Bellamya aeruginosa in the ponds. Limnodrilus hoffmeisteri was the predominant species in the canal. Comparative analysis of the impact of crab culture showed that it produced a relatively low level of disturbance but introduced large quantities of nutrients and organic matter into the canal around the farming ponds. The introduction of these substances increased the risk that Guchenghu Lake would be affected by pollution.     

Determination of a tissue and sediment threshold for tributyltin to protect prey species of juvenile salmonids listed under the US Endangered Species Act

• 1. The purpose of this report is to determine the concentrations of tributyltin in sediments that would be protective against adverse effects on prey species of salmonids listed under the US Endangered Species Act.
• 2. Two approaches for determining adverse sediment concentrations due to tributyltin (TBT) contamination are presented here. The first is the equilibrium partitioning (EqP) approach, which relies on a sediment‐water partition coefficient and toxicological data for water exposures. The EqP approach utilizes the large water quality database that has been generated over the last two decades for TBT and provides strong evidence for adverse effects at low exposure concentrations.
• 3. The second approach involves determination of a TBT tissue residue that is considered harmful for most species, which is then used to predict the sediment concentration that would likely produce this adverse tissue concentration.
• 4. Both approaches are presented here because they generally support each other but based on the information presented below, and the inherent difficulty in measuring porewater concentrations, the tissue residue approach is the recommended method for determining adverse sediment concentrations.
• 5. Using this analysis, the protective sediment concentration for TBT proposed here is 6000 ng g^?1organic carbon. Direct effects are not expected on salmonids at this sediment concentration because of their relatively short residence time in the estuary, general lack of interaction with sediment, and relatively high metabolic capacity. This concentration may ensure adequate abundance of salmonid prey species; however, it may not be low enough for the protection of sensitive benthic species.

Published in 2002 by John Wiley & Sons, Ltd.     

Effect of temperature decrease on hemocyte apoptosis of the white shrimp Litopenaeus vannamei

This study investigated the effect of continuous temperature decrease on hemocyte apoptosis of the white shrimp Litopenaeus vannamei. In the stress group, water temperature decreased from 26 to 17 °C at a rate of 1 °C/h. Shrimp kept at 26 ± 0.5 °C were used as control group. Total hemocyte count (THC), reactive oxygen species (ROS) production, cytoplasmic free-Ca²⁺ (CF-Ca²⁺) concentration, mitochondrial membrane potential (MMP), apoptotic cell ratio, and caspase-3 activity of L. vannamei hemocytes were determined when water temperature decreased to 23, 20, and 17 °C, respectively. Increased ROS production in hemocytes was observed when water temperature decreased to 20 and 17 °C. Decreased THC and cellular MMP, increased CF-Ca²⁺ concentration, apoptotic cell ratio, and caspase-3 activity were shown when water temperature decreased to 17 °C. These results indicate that water temperature decrease can induce oxidative stress on shrimp hemocytes and then cause mitochondria and caspase-3 mediated hemocyte apoptosis and THC reduction, when water temperature decreased to an unconformable level.