Differences in early developmental rate and yolk conversion efficiency in offspring of trout with alternative life histories

Partial migration, in which some individuals of a population migrate while other individuals remain resident, is generally associated with ontogenetic shifts to better feeding areas or as a response to environmental instability, but its underlying mechanisms remain relatively unknown. Brown trout (Salmo trutta) exhibit partial migration, with some individuals remaining in freshwater (freshwater resident) while others undertake an anadromous migration, where they spend time at sea before returning to breed in freshwater (migrant). We reared full‐sibling groups of offspring from freshwater‐resident and anadromous brown trout from the same catchment in the laboratory under common garden conditions to examine potential differences in their early development. Freshwater‐resident parents produced eggs that were slower to hatch than those of anadromous parents, but freshwater‐resident offspring were quicker to absorb their yolk and reach the stage of exogenous feeding. Their offspring also had a higher conversion efficiency from the egg stage to the start of exogenous feeding (so were larger by the start of the fry stage) than did offspring from anadromous parents despite no difference in standard metabolic rate, maximal metabolic rate or aerobic scope. Given these differences in early development, we discuss how the migration history of the parents might influence the migration probability of the offspring.     

Growth and osmoregulation in Atlantic salmon (Salmo salar ) smolts in response to different feeding frequencies and salinities

Groups of Atlantic salmon (Salmo salar) yearling smolts were reared in duplicate tanks supplied with freshwater or seawater, and subjected to different feeding frequencies, 100% (fed every day), 50% (fed every other day), 25% (fed every forth day) and 0% (starved), from 26 May to 26 July. After 8 weeks, all the groups were re‐fed in excess for 6 weeks. Fish were maintained on their respective a priori salinity treatments during the 6‐week follow‐up period. Starvation for a period of 8 weeks in freshwater resulted in a loss of hypo‐osmoregulatory ability when smolts were challenged with seawater and unfed smolts maintained in freshwater were unable to adapt to seawater in mid‐July. Ration levels influenced the growth rate and body size significantly. The overall growth rate was higher in freshwater than at corresponding rations in seawater. Partial compensatory growth was observed in the 0 and 25% groups following re‐feeding. Branchial Na⁺,K⁺‐ATPase (NKA) activity decreased rapidly in unfed smolts in freshwater and was the lowest in the starved group, whereas an initial increase was observed in those groups reared in seawater. After re‐feeding NKA activity differences decreased between the former feeding groups. Our results suggest that nutritional factors and/or energy levels are critical for the maintenance of hydro‐mineral balance of salmon smolts.     

Spawning success and early life history of longnose suckers in Great Lakes tributaries

Fish eggs and larvae are often subject to very high mortality, and variation in early life survival can be important for population dynamics. Although longnose suckers (Catostomus catostomus) are widespread in northern North America, little is known about their early life history. We examined fecundity and early larval survivorship during sucker spawning events in three small Lake Michigan tributaries. Although egg deposition varied 25% among spawning events, estimated larval export to the lake varied over 25,000‐fold from around 1000 to 26 million. Based on variation in environmental conditions across years, it appears that spring flow and temperature may be important determinants of egg survival to larval outmigration. Larval age data suggest that most individuals that survived to outmigration hatched during a 2‐day period despite adult spawning across at least 10 days. Most larvae spent <2 weeks in the stream and emigrated around the time of transition from endogenous to exogenous feeding before substantial growth occurred. In two of three cases, larvae drifted exclusively at night; however, high drift rates occurred during both day and night in the case where larvae were very abundant, suggesting density‐dependent drift behaviour. Our results indicate that survival in tributary streams from egg deposition to larval export is highly variable in longnose suckers. These large differences in early life survival may translate into variability in recruitment, thereby influencing population structure and dynamics.     

The role of flow dependency and water availability in fish assemblage homogenization in tributaries of the Chattahoochee River,Alabama, USA

The availability of water is becoming more variable as flow regime alterations intensify both locally and on a global scale. This pattern has been observed in the tributaries of the central Chattahoochee River System as water withdrawal and natural drought have caused flows to diminish. Stream discharge has steadily decreased in the study area by 31% over the last 50 years, and during this time, fish assemblage homogenization has occurred throughout the system. Our primary objective was to assess whether spawning mode and water availability are catalysts for fish assemblage change in tributaries of the Chattahoochee River System. We found that species which prefer or have adapted to low flow conditions (e.g. blacktail shiner Cyprinella venusta, redbreast sunfish Lepomis auritus and blackbanded darter Percina nigrofasciata) are becoming dominant and replacing historically dominant fluvial specialists. When examining short‐term changes between a dry year (2009) and a wet year (2010), some species preferring higher flows such as the highscale shiner Notropis hypsilepis were detected during the wet year, suggesting that the amount of water is important for the presence of these species in upstream reaches where they were historically abundant. Species that can reproduce successfully in low flow conditions are thriving and expanding their native ranges as more habitat becomes suitable. Species that require higher flows for part of their life cycle, however, appear to be declining from upstream areas as water availability continues to decrease, despite temporary recovery from downstream refugia during wet years.     

An investigation of the biological basis of return variability for sockeye salmon (Oncorhynchus nerka) from Great Central and Sproat lakes,Vancouver Island

We tested whether variations in stock characteristics (spawner and smolt abundance) and biotic conditions (prey variability, predation, competition) during the early marine period explained variations in the return of sockeye salmon (Oncorhynchus nerka) to Great Central and Sproat lakes, adjacent lakes on the west coast of Vancouver Island. There are two freshwater age groups in each lake; fish spend 1 or 2 yrs in freshwater after hatching. We tested the influences of stock and biotic factors on the return of each of the two age groups from each of the two lakes. Results of regression analyses showed that prey biomass variability best explained the variation in return for all lake‐age groups. Euphausiid (Thysanoessa spinifera) and cladoceran (Evadne) prey biomass variability explained between 0.75 and 0.95 (adjusted R²) of the variation in return. There appear to be instances of a mismatch between the seasonality of prey productivity and the apparent critical period of feeding for juvenile sockeye.     

The effects of changing feeding frequency simultaneously with seawater transfer in Atlantic salmon Salmo salar L. smolt

The effects on group feed intake and growth performance of changing feeding frequency simultaneously with seawater transfer of Atlantic salmon Salmo salar were investigated. Two feeding regimes of one feed per day (1F) and eight feeds per day (8F) were compared for groups of Atlantic salmon in freshwater. Following seawater transfer groups were either fed on their pre-transfer regimes or swapped to the other regime, resulting in four treatments (n = 3). Regardless of the pre-transfer feeding regime, 1F groups had significantly (P < 0.05) lower feed intake immediately following transfer than 8F groups. However, groups that underwent a change in feeding frequency did not have significantly lower feed intake immediately following transfer than those kept on the pre-transfer feeding regime. During the freshwater phase, overall mean feed intake of 8F groups was significantly greater than 1F groups, whilst there was no significant difference in mean feed intake for any of the treatments during the seawater phase. Growth was better in groups fed 8F in freshwater than those fed 1F in freshwater regardless of post-transfer feeding regime. There were no significant differences in growth depensation throughout the experiment, suggesting that there were no overall differences in hierarchy strength amongst treatments. The main finding of this experiment was that a single meal per day immediately following seawater transfer results in initially significantly lower feed intake than the higher feeding frequency regardless of pre-transfer feeding regime, consequently multiple daily feeds is the recommended feeding regime following seawater transfer.     

Abnormal elongation of the lower jaw in juvenile Japanese flounder: combined effects of a rotifer diet enriched with <Emphasis Type="Italic">Nannochloropsis</Emphasis> preserved by various methods and parentage

To elucidate possible causes of skeletal malformations in larval Japanese flounder, we reared larvae fed rotifers enriched with three types of preserved Nannochloropsis (fresh, refrigerated, and frozen). The incidence of malformations at 50 days post hatch ranged from 14.5 to 38.5 % within the three experimental groups, and elongation of the lower jaw (LJ) was the most frequently observed malformation, ranging from 68 to 89 % of total malformations. We also investigated larval parentages using microsatellite markers. Parentage analysis of the fresh Nannochloropsis group showed that one sire and a pair generated significant numbers of LJ-elongated individuals. In the refrigerated Nannochloropsis group, one dam and two sires generated significant numbers of LJ-elongated individuals. In the frozen Nannochloropsis group, no broodstocks or pairs generated significant numbers of LJ-elongated individuals. Our results suggest that LJ elongation in Japanese flounder likely results from the application of different types of preserved Nannochloropsis during rotifer feeding stage. However, there is also some level of genetic influence associated with this deformity.     

Migration strategies of brown trout (Salmo trutta) in a subarctic river system as revealed by stable isotope analysis

We estimated the proportions of anadromous and freshwater‐resident brown trout (Salmo trutta) in different parts of the subarctic River Näätämöjoki/Neidenelva system (Finland and Norway) using carbon, nitrogen and hydrogen stable isotope analyses of archived scales as identifiers of migration strategy. Our results showed that carbon stable isotope values were the best predictor of migration strategy. Most individuals fell into two clearly distinct groups representing anadromous (47%) or freshwater‐resident (42%) individuals, but some fish had intermediate carbon values suggesting repeated movement between freshwater and the sea. The proportion of anadromous individuals decreased steadily with distance from the sea forming a spatial continuum in migration strategies which is probably maintained by the combination of several factors such as divergent availability of food resources, variable migration costs and genetic differences. These within‐catchment differences in migration strategies should be taken into account in fisheries management practices.     

Genetic variation and the relationship between stream and lake ecotypes of a threatened desert Catostomid,the Warner sucker (Catostomus warnerensis)

Many fish species exhibit diverse life history strategies that help maintain population viability. An understanding of the relationships among these strategies is crucial for prioritising conservation actions. The Warner sucker, endemic to the Warner Lakes Basin in southern Oregon, USA, is one example of a taxon where a lack of information regarding relationships among life history strategies has hampered conservation efforts. Warner suckers have two distinct life history types: stream‐type fish that have a fluvial life history and lake‐type fish that have an adfluvial life history. There are advantages and disadvantages associated with each life history, and presently the relationship between life history types is not well understood. Our objectives were to determine the amount of genetic variation within and among tributary populations of Warner suckers and to determine the origins of suckers collected in the Warner Lakes. We collected individuals from four tributary populations, a refugial population, and Hart and Crump lakes and genotyped them at 16 microsatellite loci. Estimates of genetic variation among populations suggested low levels of gene flow (F_ST = 0.153) and genetic variation among populations seemed to be influenced by population and habitat characteristics. Nearly all of the individuals collected in Hart and Crump lakes originated in a single tributary, Deep Creek, which likely reflects reduced habitat connectivity between most other tributaries and the Warner Lakes. Data presented in this study are useful for evaluating the status of Warner sucker populations and for prioritising conservation actions such as the removal and modification of barriers.     

The effects of trout culture on diet and food availability of native freshwater fish populations

Cultivation of a species or population and distribution to various regions has raised the idea of negative impacts on native species. The effect of non‐native species on native species may be caused by competition for source, predation, hybridization, and parasite/disease transport. The present study aims to evaluate the possible effects of a trout farm established on the banks of Kocaba? Stream (Çanakkale, Turkey) on feeding characteristics of some freshwater fish (Phoxinus phoxinus, Barbus oligolepis, and Squalius cii). The samples were collected monthly over a year at two stations located before and after the trout farm and at a control station on the tributary not impacted by the effects of the farm. Fish and environmental samples were gathered monthly with an electroshocker and some fishing tools between August 2015 and July 2016. The fish diet and resource incorporation into biomass were evaluated by gut content and stable isotope analyses. Changes in diet preferences when the species are exposed to source stresses and some individuals fed on farm‐based feed contaminated from the farm in Kocaba? Stream. In this study, it was observed that native fish populations in aquaculture regions were influenced by diet preferences. Designing enclosed systems limiting feed and waste transit in aquaculture establishments may be suitable for sustainability of these species.     

Effect of Salinity on Larval Rearing of Pacu,Piaractus mesopotamicus,a Freshwater Species

The aim of this study was to evaluate the growth and survival of pacu, Piaractus mesopotamicus, larvae reared in different salinities and to determine the Artemia nauplii life span in freshwater and in saline water. First feeding 5‐d‐old pacu larvae were reared in freshwater or at 2, 4, 6, 8, 10, 12, and 14 ppt salinities. The larvae were reared in 1.5‐L aquaria at a density of 10 larvae/L with three replicates per treatment. After 10 d of rearing, significant differences (P < 0.05) were observed for growth and survival. Larval growth was higher at 2 and 4 ppt, and survival at 2 ppt was 100%. In freshwater and at 4, 6 and 8 ppt, the survival was 91.1, 93.3, 73.3, and 39.9%, respectively. At higher salinities, there was 100% mortality after 2 h (12 and 14 ppt) and 8 h (10 ppt) of exposure. The slightly saline water of at least 2 ppt increased the Artemia nauplii life span compared to the life span in freshwater. Later, in a second trial, 5‐d‐old pacu larvae were reared in freshwater and at 2 and 4 ppt salinities during the first 5 or 10 d of active feeding, and then the fish were transferred to freshwater. At the end of 15 d, larval growth was lower in freshwater (42 mg) than in treatments 2 and 4 ppt (59–63 mg). The abrupt transfer of fish from freshwater to slightly saline water and the return to freshwater did not affect the survival rates (89–97%). The larvae were able to adapt to these saline environments and handle abrupt changes in salt concentration. We concluded that salinity concentration of 2 ppt can be used for pacu larval rearing, allowing the Artemia nauplii lifetime to last longer and cause faster fish growth.     

Dusky dolphin foraging habitat: overlap with aquaculture in New Zealand

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Feed-growth relationships of Arctic charr transferred from freshwater to saltwater at different seasons

Groups of Arctic charr, Salvelinus alpinus (L.), originating from an anadromous stock, were transferred directly from freshwater to seawater (35 S), from freshwater to brackish water (20 S), or were gradually adapted to seawater over a period of 10 days. A control group was kept in freshwater. Feed intake and growth were then monitored during the following 59 days. Two experiments were carried out, one during winter (December–January) and the other during summer (June–July). Water temperature was maintained at 8 C. All fish had been held under natural photoperiod and temperature conditions from the end of the first feeding period (mid-April) until the experiments were carried out. Rates of growth did not differ between the groups of charr held in fresh- and brackish water, but growth of these groups was better than that of fish reared in seawater. Relationships between individual feed intake (FI) and individual specific growth rates (SGR), within groups were expressed as: ln (SGR+1) = a + ln (FI+1), and regression lines were compared using analysis of covariance. In winter, the regression line for fish transferred directly to seawater had a significantly steeper slope, and a lower elevation, than the lines for fish transferred to brackish water or held in freshwater. Fish transferred gradually to seawater had an intermediate position. In summer, the regressions for all groups were parallel with intercepts in the seawater groups being significantly lower than in the freshwater group. This indicates that the gross feed conversion efficiency (FCE) in Arctic charr was lower in seawater than in freshwater. The results are discussed in relation to digestion, gut function and osmoregulation. yc]Keywords xc]Arctic charr (Salvelinus alpinus (L.)) xc]Feed utilization xc]Salinity xc]Season     

The north‐west of the Iberian Peninsula is crucial for conservation of Margaritifera margaritifera (L.) in Europe

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Growth,survival and fatty acid composition of Rhamdia quelen (Quoy and Gaimard, 1824) larvae fed on artificial diet alone or in combination with Artemia nauplii

Black catfish (Rhamdia quelen) is a species of interest for aquaculture in Brazil, Argentina and Uruguay. A feeding trial was conducted to evaluate the effect of feeding R. quelen larvae on either only an artificial diet or in combination with Artemia nauplii (AN) on larval performance and fatty acid composition. For 12 days, larvae were fed from first feeding (3 days after hatching, TL = 5.88 ± 0.23 mm) with artificial food only or a combination of artificial food and AN (co‐feeding). At the end of the trial, total length of co‐fed larvae was significantly higher than that of larvae fed solely artificial food (P < 0.001). No significant differences were found in survival rates. Co‐feeding microdiet with a small amount of AN significantly affected larval fatty acid composition. Lipid and fatty acid composition of food and larvae revealed the importance of n‐3 fatty acids for growth of black catfish larvae and that, as most freshwater fish, R. quelen larvae can elongate and desaturate linolenic acid to n‐3 highly unsaturated fatty acids. Results suggest that R. quelen larvae can be fed from first feeding on microdiets as unique food source, although better larval performances are obtained by co‐feeding with a small amount of AN.     

Fishers,dams, and the potential survival of the world's rarest turtle,Rafetus swinhoei,in two river basins in northern Vietnam

1. Next to cetaceans and megafishes, freshwater turtles are the most iconic endangered freshwater species.
2. A detailed questionnaire survey conducted with more than 100 individuals from fishing communities in northern Vietnam was used to investigate the current status of Southeast Asian turtles and provides new hope concerning the survival of Rafetus swinhoei, for which recent official records in the wild are limited to a single individual in Vietnam.
3. The survey included the entire Vietnamese portion of the Da River in Hoa Binh and Son La provinces, as well as the Chu and Ma river system in Thanh Hoa Province, as they are the last sites where the world's rarest and largest Asian softshell turtle has been seen. The questionnaire, conducted in Vietnamese, focused on demographic details, fishing intensity and gear, the status of fishing grounds, and the frequency of interaction with turtles.
4. The great majority of fishers could recognize different turtle species from photographs and describe their preferential breeding habitats; not all knew that they are protected. A few confirmed that more than once each year they still encounter freshwater turtles during their fishing activities.
5. This survey provides detailed information on sites where freshwater turtles are still seen in northern Vietnam and broadens our hope that wild individuals of the extremely rare R. swinhoei may still be present in the remaining riparian wetlands of these biodiverse, dammed, and controlled river basins in North Vietnam.

     

Comparative genomic insights into the taxonomy of Edwardsiella tarda isolated from different hosts: Marine,freshwater and migratory fish

Edwardsiella tarda, a Gram‐negative member of the family Enterobacteriaceae, has been isolated from many animal species worldwide, especially fish species. Its broad host range indicates the diversity in taxonomy, which attracted the attention of many researchers. Here, we added genome of E. tarda strain isolated from freshwater fish to comparative genomics study for the first time. We sequenced and assembled the genome of E. tarda ASE201307 which was isolated from freshwater Asian swamp eel. ASE201307 genome contained a single circular chromosome of 3.68M with G+C 57.09% content. Comparative genomics including SNP calling, synteny block, Core/Pan genes analysis and phylogeny analysis was conducted among ASE201307 and other Edwardsiella strains isolated from different fish species. Results of SNP analysis and synteny block demonstrated the close relative of ASE201307, FL95.01 and DT which were all isolated from freshwater fish. In further analysis heat map of dispensable genes and phylogenetic tree, all E. tarda strains were divided into two groups. One was isolated from freshwater fish and the other was isolated from marine/migratory fish. Based on all studies above, we proposed the living environment of hosts as a new taxonomic character and divided E. tarda isolated from diseased fish into freshwater group and marine/migratory group.     

Do Eurasian minnows (Phoxinus phoxinus L.) inhabiting brackish water enter fresh water to reproduce: Evidence from a study on otolith microchemistry

Dynamics of coastal fish assemblages in the Baltic Sea are still rather poorly understood. In particular, little information is available on migrations and movements of the small‐bodied littoral fish species like Eurasian minnow (Phoxinus phoxinus L.). Minnow is considered typically as a river and lake species, but it also inhabits brackish coastal waters of the Baltic Sea. In this study, we investigated movement patterns of brackish water inhabiting minnows using otolith microchemistry. Fish were collected from four different sites (from two bays and two stream mouths) around Saaremaa Island. The results indicated that at least three distinct migration patterns exist: (i) seawater residency, (ii) fast springtime migrations to fresh water or to bays with lower salinities (areas near stream mouths) and (iii) prolonged migrations to fresh water (some cases overwintering in streams). Migration patterns listed above were not evenly distributed among sites, and some individuals did not migrate to fresh water in every year. None of the analysed fish were freshwater residents. Additionally, potentially ontogenetic effects on Mn and Sr concentrations were observed in the otolith core regions, which may have important implications for the interpretation of otolith chemistry data. The overall findings of this study demonstrate that much more complex migration patterns exists in brackish water inhabiting minnow populations than previously thought and at least some individuals do enter freshwater to reproduce.     

Dominance hierarchies in Arctic charr, Salvelinus alpinus L.: differential cortisol profiles of dominant and subordinate individuals after handling stress

We examined the effect of social rank on plasma cortisol dynamics after handling stress in juvenile Arctic charr, Salvelinus alpinus L., reared in groups of 200 individuals in 1.5 m³ circular tanks (rearing density 0.022 kg L^–1). Fish obtained by dip-netting were categorized as either socially subordinate, dominant or as holding an intermediate position on the basis of size, skin coloration and occurrence of bite marks. In undisturbed fish, the highest cortisol levels were found in fish ranked as intermediate and the lowest in dominant fish. In contrast to what has been found under conditions of artificial rearing in small groups (two to ten individuals), cortisol was not significantly elevated in subordinates compared with dominant individuals. In small groups of fish, aggressive interactions and restricted access to food may be significant factors leading to increased stress in socially subordinate individuals. Following stress by dip-netting and transfer, the quickest and largest cortisol response was seen in dominant individuals. These results suggest that hypothalamus–pituitary–inter-renal/adrenal axis responsiveness as well as baseline cortisol production is influenced by social rank in fish, as has been shown in other vertebrates.     

Effect of dietary Clostridium butyricum and different feeding patterns on growth performance,antioxidant and immune capacity in freshwater prawn (Macrobrachium rosenbergii)

An 8‐week study was conducted to evaluate the effects of different feeding patterns with dietary Clostridium butyricum supplementation on growth performance, antioxidant and non‐specific immune responses in freshwater prawn, Macrobrachium rosenbergii (0.39 ± 0.001 g). There were four feeding methodologies: feeding basal diet continuously (P1); feeding diet with 500 mg/kg C. butyricum continuously (P2); feeding diet with 500 mg/kg C. butyricum 5 days after 2 days of basal diet (P3) and feeding diet with 500 mg/kg C. butyricum 2 days after 5 days of basal diet (P4). The results revealed that prawns in P3 had the highest weight gain rate (WGR) and lowest feed conversion ratio (FCR) than the other groups. Haemolymph total protein levels and superoxide dismutase activity increased significantly in P2, P3 and P4 groups, while malondialdehyde content and anti‐superoxide anion levels decreased significantly compared to control. The mRNA expression of intestinal dorsal and Toll in P2 and P3 groups decreased significantly compared to control. Prawns in P3 exhibited improved growth performance, increased antioxidant capacity and enhanced immune function. We concluded that feeding diet with 500 mg/kg C. butyricum for 5 days after 2 days of basal diet was recommended for M. rosenbergii.