The effect of lake morphometry on thermal habitat use and growth in Arctic charr populations: implications for understanding climate‐change impacts

Oxygen stable isotope temperature reconstruction methods were used to estimate mean experienced summer temperatures from growth zones within individual Arctic charr otoliths sampled from lakes with contrasting morphologies but proximate locations. For either lake, otolith‐estimated temperatures were not significantly related to back‐calculated growth. Fish in the smaller lake evidenced an increase in growth with age related to increasing use of cooler thermal habitats, with the use of thermal habitat possibly governed by predation risks. No relationships between age, growth or temperature were observed in the larger lake. Significant negative effects on back‐calculated growth were observed due to increasing air temperatures in the smaller and shallower lake, possibly owing to warmer surface and littoral waters and a limited amount of preferred cool‐water habitat. A similar relationship was not observed in the larger and deeper lake and indicated that resident Arctic charr were not as vulnerable to the impacts of temperature warming, possibly because of better behavioural thermoregulation opportunities in the cooler, deeper lake. Results provide evidence for differing climate‐influenced growth outcomes among proximately located populations, with outcomes likely to depend on the differences among habitats, including lake size and morphometry which may act to influence fish densities in available preferred thermal habitats.     

Latitudinal variation in growth and otolith‐inferred field metabolic rates of Canadian young‐of‐the‐year Arctic charr

Countergradient variation (CGV) is defined as genetic variation that counteracts the negative influences of the physical environment, minimising phenotypic variability along an environmental gradient. CGV is thought to have relevance in predicting the response of organisms to climate variability and change. To test the hypothesis that growth rate increased with latitude, consistent with CGV, young‐of‐the‐year (YOY) Arctic charr, Salvelinus alpinus, were examined along a ~27° latitudinal gradient in central and eastern Canada. Growth rates were estimated from fork lengths standardised by the thermal opportunity for growth based on experienced water temperatures derived using otolith oxygen stable isotopes. Results demonstrated patterns consistent with CGV, where northern populations demonstrated faster growth rates. A secondary aim was to test for similar geographical patterns in otolith‐inferred metabolic rates, which reflect the energetic costs of standard metabolic rate (SMR) and other processes such as feeding, locomotion, thermoregulation, reproduction and growth. Results demonstrated a significant, positive relationship between otolith‐inferred metabolic rate and latitude, which may reflect an increase in one, or a combination, of the above‐noted physiological processes. The similar latitudinal pattern in growth and otolith‐inferred metabolic rates suggests greater intake of food per unit of time by northern fish. The phenotypic variation in physiological traits observed here demonstrates the significant adaptability of Arctic charr to different thermal regimes with different growing season lengths. Determining the relative contributions of phenotypic plasticity and genetic variation to the observed latitudinal variation will be critical to predicting the responses of Arctic charr to climate change more accurately.     

Evidence for genetic distinction among sympatric ecotypes of Arctic char (Salvelinus alpinus) in south‐western Alaskan lakes

Resource polymorphism may play an important role in the process of speciation. The Arctic char (Salvelinus alpinus) exhibits great phenotypic and genetic diversity across its range, making it an ideal species for studies of resource polymorphism and divergence. Here, we investigated genetic variation at 11 microsatellite loci among 287 Arctic char from five isolated yet proximate postglacial lakes in south‐western Alaska that were previously examined for resource polymorphism. Significant differences in pairwise F_ST were detected among all lakes (range from 0.05 to 0.28, all P < 0.02). In one lake (Lower Tazimina Lake), we found evidence for two genetic groups of char and for significant differences in the distribution of microsatellite variability among at least two of the three previously described body size morphotypes (‘large’‐, ‘medium’‐, and ‘small’‐bodied char; maximum F_ST = 0.09; differences in admixture proportions). We also found a significant association between genetic admixture proportions and gill raker counts among body size morphs (r = ?0.73, P < 0.001). Our data represent the first record of genetically distinct sympatric morphs of Arctic char in Alaska and provide further evidence that differences in morphology associated with feeding (gill rakers) and growth trajectories reflect niche diversification and promote genetic divergence in Holarctic populations of Arctic char.     

Declines in the energy content of yearling non‐native alewife associated with lower food web changes in Lake Michigan

Juveniles of non‐native alewife, Alosa pseudoharengus (Wilson), were collected in Lake Michigan in 1998, 1999, 2010, 2011 and 2013 to evaluate changes in energy content during a period of major ecosystem changes. Consistent with historical data, energy content of yearling alewife declined from late winter into late spring and was at its lowest point in June. Energy density and length‐adjusted, entire‐body energy were lower in 2010, 2011 and 2013 than in 1998 and 1999. Energy losses over the first winter in the lake were more severe for the 2010 year class (56% decrease) than for the 1998 year class (28% decrease). Alewife diets in late spring of 2010–2013 reflected the loss of major prey such as Diporeia spp. and a shift towards lower energy prey. The recent decline in energy content of yearling alewife can be linked to recent changes in productivity and abundance of key components of the lower food web of Lake Michigan following the dreissenid invasion.     

Trophic dynamics of a reservoir fishery following an introduction of a top predator: Insights from stable carbon and nitrogen isotopes

Trophic dynamics and conceptual niche spaces of top piscivores were assessed using stable isotope analysis following the introduction of hybrid striped bass Morone saxatilis (Walbaum) × Morone chrysops (Rafinesque) into an established reservoir fishery devoid of gizzard shad, Dorosoma cepedianum (Lasueur). Hybrid striped bass were initially stocked into Three Mile Lake, Iowa as an attempt to biologically control pervasive yellow bass, Morone mississippiensis Jordan & Eigenmann, populations. From the analyses, it concluded that hybrid striped bass predominately targeted prey fish located in the littoral habitats of the reservoir and did not selectively consume yellow bass as intended. Bayesian isotope mixing models described the diets of hybrid striped bass to include a variety of prey fish, predominantly consisting of young bluegill Lepomis macrochirus and yellow bass. Food resource overlap among hybrid striped bass, largemouth bass, Micropterus salmoides Lacépède, and walleye, Sander vitreus (Mitchill), appeared substantial based on the isotopic niche overlap model. Results from this case study, in conjunction with the hindsight that yellow bass populations became prolific even with stockings of hybrid striped bass, suggest that their use to control yellow bass populations may not be a viable management strategy in southern Iowa.     

Diverse juvenile life‐history behaviours contribute to the spawning stock of an anadromous fish population

Habitat quality often varies substantially across space and time, producing a shifting mosaic of growth and mortality trade‐offs across watersheds. Traditional studies of juvenile habitat use have emphasised the evolution of single optimal strategies that maximise recruitment to adulthood and eventual fitness. However, linking the distribution of individual behaviours that contribute to recruitment at the population level has been elusive, particularly for highly fecund aquatic organisms. We examined juvenile habitat use within a population of sockeye salmon (Oncorhynchus nerka) that spawn in a watershed consisting of two interconnected lakes and a marine lagoon. Otolith microchemical analysis revealed that the productive headwater lake accounted for about half of juvenile growth for those individuals surviving to spawn in a single river in the upper watershed. However, 47% of adults had achieved more than half of their juvenile growth in the downstream less productive lake, and 3% of individuals migrated to the estuarine environment during their first summer and returned to freshwater to overwinter before migrating back to sea. These results describe a diversity of viable habitat‐use strategies by juvenile sockeye salmon that may buffer the population against poor conditions in any single rearing environment, reduce density‐dependent mortality and have implications for the designation of critical habitat for conservation purposes. A network of accessible alternative habitats providing trade‐offs in growth and survival may be important for long‐term viability of populations.     

Successful rearing of whiteleg shrimp Litopenaeus vannamei larvae fed a desiccation‐tolerant nematode to replace Artemia

The nematode Panagrolaimus sp. was tested as live feed to replace Artemia nauplii during first larval stages of whiteleg shrimp Litopenaeus vannamei. In Trial 1, shrimp larvae were fed one of four diets from Zoea 2 to Postlarva 1 (PL1): (A) Artemia nauplii, control treatment; (NC) nematodes enriched in docosahexaenoic acid (DHA) provided by the dinoflagellate Crypthecodinium cohnii; (N) non‐enriched nematodes; and (Algae) a mixture of microalgae supplemented in C. cohnii cells. In Trial 2, shrimp were fed (A), (NC) and a different treatment (NS) with nematodes enriched in polyunsaturated fatty acids (PUFAs) provided by the commercial product S.presso^®, until Postlarva 6 (PL6). Mysis 1 larvae fed nematodes of the three dietary treatments were 300 μm longer (3.2 ± 0.3 mm) than control larvae. At PL1, control shrimp were 300 μm longer (4.5 ± 0.3 mm) than those fed DHA‐enriched or PUFAs‐enriched nematodes. No differences were observed in length and survival at PL6 between control larvae and those fed DHA‐enriched nematodes (5.1 ± 0.5 mm; 33.1%–44.4%). Shrimp fed microalgae showed a delay in development at PL1. This work is the first demonstration of Panagrolaimus sp. suitability as a complete substitute for Artemia in rearing shrimp from Zoea 2 to PL6.     

Coupling stable isotope studies with food web manipulations to predict the effects of exotic fish: lessons from Cuatro Ciénegas,Mexico

• 1. Exotic species threaten native species worldwide, but their impacts are difficult to predict.
• 2. Stable isotope analysis was combined with field competition experiments to predict how an invasive African cichlid fish, Hemichromis guttatus, might affect native fish in the desert springs of Cuatro Ciénegas, Mexico.
• 3. Stable isotope analysis suggested diet overlap between the invader and juvenile endemic cichlids, and field experiments verified that the invader reduces growth rates of the juvenile endemics through competition, but has smaller effects on adults.
• 4. Competition between juvenile endemic cichlids and the invader was asymmetric, with the exotic out‐competing the native, suggesting the potential for competitive exclusion if the invasion is not stopped.
• 5. These results suggest that exotic removal programmes in Cuatro Ciénegas should focus on removing/reducing populations of the exotic cichlid in habitats where juvenile native cichlids are concentrated.
• 6. This approach could help focus efforts to manage exotic species before populations of native species have crashed, when it is too late to intervene.

Copyright © 2011 John Wiley & Sons, Ltd.     

Growth differences of Japanese eels Anguilla japonica between fresh and brackish water habitats in relation to annual food consumption in the Kojima Bay‐Asahi River system,Japan

To learn about the relationships between feeding and growth of temperate eels in freshwater and brackish water habitats, we analysed 533 yellow‐phase Japanese eels Anguilla japonica collected in both types of habitats in southeastern Japan. Because male eels were very rare in each habitat (FW, N = 1; BW, N = 20), characteristics of female eels were compared between the different habitats. Annual food consumption was evaluated with the consideration of instantaneous food consumption and annual activity period. Stomach fullness index (stomach content weight/body weight) was used as an indicator of instantaneous food consumption. The ratios of number of months with eel catch to those when eel sampling was conducted were used as an indicator of activity period. Female yellow eels tended to be older and slower growing in fresh water (N = 78; age, mean ± SD = 7.9 ± 2.4 years; growth rate, 59.8 ± 14.0 mm year^?1) than in brackish water (N = 229; age, 5.5 ± 1.8 years; growth rate, 90.1 ± 24.4 mm year^?1). Irrespective of sex, yellow eels in brackish water had a higher stomach fullness index and a greater ratio of months with eel catches, indicating greater annual food consumption by brackish water eels. These results indicate that greater annual food consumption contributes to the greater growth rates of Japanese eels in brackish water habitats.     

Effect of using sodium bicarbonate to adjust the pH to different levels on water quality,the growth and the immune response of shrimp Litopenaeus vannamei reared in zero‐water exchange biofloc‐based culture tanks

The bioflocs technology proved to be a sustainable technique used in zero‐water exchange shrimp culture systems. However, the pH and alkalinity may decrease due to the biofloc formation process and Nitrification. A 48‐day experiment was performed to investigate the effects of different pH (7.1–7.6; 7.6–8.1) conditions on water quality, the growth and the health status of shrimp in biofloc technology (BFT) through using sodium bicarbonate to adjust pH respectively. Two pH treatments and one control were compared: T0 — control, T1 — pH 7.6 — NaHCO₃, T2 — pH 8.1 — NaHCO₃, each treatment consisted of three replicate tanks (90 L water volume) and each replicate stocked with 30 shrimp (equivalent to 333 shrimp m^?3). Significant physical, chemical and biological differences (P < 0.05) were detected among treatments. At the end of the experiment, water quality, the growth and the immune response of shrimp in control were significantly lower (P < 0.05) than the other treatments. Moreover, the T2 treatment had a better performance in these three aspects. The results indicated that it was necessary to adjust the pH and alkalinity in the BFT, and a higher pH as well as alkalinity for shrimp growth and the stability of the BFT were more favourable.     

Co‐Infection with Pseudomonas anguilliseptica and Delftia acidovorans in the European eel,Anguilla anguilla (L.): a case history of an illegally trafficked protected species

Inspections by customs agents at Barcelona airport discovered 420 kg of contraband glass eels prepared for shipment to Hong Kong. After confiscation of these animals by police, they were transported to holding facilities to be maintained until after a judicial hearing. Upon arrival, they were separated into two groups and held under ambient flow‐through conditions in fresh water. During their captivity period, several peaks in mortality occurred and multiple bacterial strains were isolated from moribund animals. Sequencing of 16S rDNA was used to determine specific identity of the isolates. An initial isolation of Pseudomonas anguilliseptica was treated with oxytetracycline. A subsequent isolation of Delftia acidovorans proved resistant to oxytetracycline and was treated with gentamicin in combination with sulphadiazine–trimethoprim. Once the health condition of the animals was stabilized, they were partitioned into groups and subsequently released as part of a restocking effort for the species following the guidelines of Regulation (EC) 1100/2007 (Anon 2007). This represents the first record for both bacterial species in the host Anguilla anguilla in the Spanish Mediterranean.     

Response of the intestinal mucosal barrier of carp (Cyprinus carpio) to a bacterial challenge by Aeromonas hydrophila intubation after feeding with β‐1,3/1,6‐glucan

The effect of dietary β‐glucan on the bacterial community in the gut of common carp (Cyprinus carpio) was examined after oral application of Aeromonas hydrophila. Carp received either feed supplemented with 1% MacroGard^®, a β‐1,3/1,6‐glucan, or a β‐glucan‐free diet. Fourteen days after feeding, half of the carp from each group were intubated with 10⁹ colony‐forming units (CFU) of a pathogenic strain of A. hydrophila. Gut samples were taken 12 hr to 7 days after application and analysed using microbiological and molecular biological techniques (NGS, RT‐PCR‐DGGE). The reaction of the mucosa and the microbiota to an A. hydrophila intubation differed in carp fed with β‐glucan compared to carp from the control group. In β‐glucan fed carp, the total bacterial amount was lower but the number of bacterial species was higher. Bacterial composition was different for carp from both treatment groups. The number of mucin filled goblet cells was reduced in carp fed the β‐glucan diet. Mucus was obviously released from the goblet cells and was probably washed out of the gut together with high numbers of bacteria. This might be protective against pathogenic bacteria and, therefore, feeding with β‐glucan may provide protection against infections of the gut in carp.     

Dietary taurine supplementation to a plant protein source‐based diet improved the growth and intestinal immune function of young grass carp (Ctenopharyngodon idella)

The effects of taurine supplementation on the growth and intestinal immune function in young grass carp (Ctenopharyngodon idella) were investigated in this study. A total of 540 fish (initial average weights of 255.74 ± 0.65 g) were fed one fishmeal diet and five all‐plant protein source‐based diets with graded levels of taurine (0 to 1.98g/kg diet) for 60 days, and then challenged with Aeromonas hydrophila for 14 days. First, the results showed that the taurine supplementation improved growth (PWG, TGC, FI and FE), enteritis resistance, intestinal antimicrobial compounds (LZ, ACP, C3, C4, IgM, hepcidin, LEAP‐2A, LEAP‐2B, β‐defensin‐1 and MUC2) and attenuated intestinal inflammation in young grass carp under the all‐plant protein source‐based diet. Second, the taurine supplementation attenuated intestinal inflammation partially referring to nuclear factor kappa B (NF‐κB) and target of rapamycin (TOR) signallings. Finally, under the all‐plant protein source‐based diet, the comparable level of taurine supplementation based on growth and ability against enteritis relative to fishmeal diet was established as 0.50 g/kg diet, and the optimal levels of taurine supplementation based on thermal‐unit growth coefficient (TGC), ability against enteritis and acid phosphatase (ACP) activity were established as 0.97, 1.08 and 1.21 g/kg diet, respectively.     

Antifungal effect of Origanum onites essential oil as an alternative to formalin in the artificial incubation of narrow‐clawed crayfish (Astacus leptodactylus Eschscholtz, 1823)

As alternative to formalin, the antifungal effect of a plant product [Origanum onites L. (Lamiaceae) oil] was investigated for use in the artificial incubation of narrow‐clawed crayfish (Astacus leptodactylus Eschscholtz) eggs. For this purpose, this study was conducted as two experiments. In experiment I, the eggs were artificially incubated for 40 days. In experiment II, juveniles were cultured to determine effects of O. onites oil on juveniles for 30 days. The experimental groups were as follows: formalin (3500 ppm for 15 min), O. onites oil (300 ppm for 15 min, 700 ppm for 2 min and 1000 ppm as a dip treatment 15 split‐second) and a control (no treatment). In the experiment I, the highest hatching rate (86%) and survival rate of stage II juveniles (80%) were observed in 1000 ppm dip group. These results were similar to that of formalin group (85% and 79%) respectively. The control group exhibited the lowest hatching rate (49%) and stage II rate (42%) compared with the 1000 ppm dip group and 3500 ppm formalin treatments. However, other concentrations (300 and 700 ppm) of O. onites showed toxic effects on the eggs and there was no hatching. In the experiment II, the survival rate and growth performance of the crayfish juveniles were similar in all groups. This study indicated that the 1000 ppm O. onites dip treatment could be a good alternative to formalin for improved egg hatchability in the artificial incubation of crayfish eggs.     

Changes in ovary and testis and breeding fitness of the climbing perch,Anabas testudineus (Bloch, 1792), exposed to sub‐lethal concentrations of monocrotophos

Monocrotophos (MCP) is one of the organophosphate pesticides extensively used in agriculture and animal husbandry. The present study reports the effects of sub‐lethal concentrations of MCP on gonadosomatic index (GSI), gonadal histology and breeding fitness of the fish Anabas testudineus. The fish were exposed to three sub‐lethal concentrations of monocrotophos (T1: 3.5 mg/L, T2: 5.3 mg/L and T3: 10.6 mg/L) for 45 days with 12 fish (males and females in equal numbers) in each tank, and one group was kept as control (C) without any treatment. GSI decreased in all treatment groups in comparison with control. Significant decrease in fertilization and hatching rate was observed at all concentrations in comparison with control on 15, 30 and 45 days of monocrotophos exposure. The decreased vitellogenesis, disruption of follicular wall and oocyte atresia were observed in all the treated females at 30 and 45 days of exposure. Rupture of seminiferous tubules was noticed in all the treated males irrespective of exposure periods. The results thus indicated that monocrotophos could deleteriously impact the gonadal structure and function in A. testudineus, which could seriously impact the reproductive success of the animal.     

Quantification of waste feed and fish faeces in sediments beneath yellowtail pens and possibility to reduce waste loading by co‐culturing with sea cucumbers: an isotopic study

To evaluate environmental impacts of yellowtail culture and to examine the efficiency of the sea cucumber Apostichopus japonicus in reduction of waste loading, surface sediments were sampled and A. japonicus were cultured at a yellowtail farm in Owase Bay, Japan. Waste feed‐ and faeces‐derived organic matter (WOM, FOM) in sedimentary organic matter (SOM) was estimated based on the δ¹³C and δ¹⁵N of the fish feed (?21.7‰, 9.2‰), yellowtail faeces (?20.6‰, 6.2‰) and SOM reference (?24.4‰, 4.4‰). Small WOM (0–22% in SOM) but substantial FOM (28–61%) loadings in the fish farm area and high sulphide concentrations in the sediments (1.0 mg g^?1) suggest that reduction in the fish stocks or mitigation of the faeces should be considered. A. japonicus juveniles were cultured in three cages deployed below a pen and growth was assessed after three different periods (62, 107, 181 days). A. japonicus grew well during the first 107 days (daily specific growth rate, 3.7%) and their survivorship was high (80–90%). Growth ceased after 107 days, probably due to fouling on the cages. The δ¹³C and δ¹⁵N of their hypothetical diet (–19.7‰, 5.5‰) were close to the FOM values, suggesting assimilation of FOM.     

Screening of a high bioflocculant‐producing bacterial strain from an intensive fish pond and comparison of the bioflocculation effects with Rhodococcus erythropolis

A high bioflocculant‐producing bacterial strain BX‐13 isolated from an intensive fish pond by multiple subcultures and measured through primary screening and rescreening using kaolin. The strain BX‐13 was identified to belong to the same branch as Bacillus subtilis by morphological, physiological and biochemical, 16S rDNA gene sequencing, Blast homology search and multiple sequence alignments. The bioflocculation potential of BX‐13 and Rhodococcus erythropolis was compared, using water from the intensive pond where BX‐13 was isolated. The results showed the number of colonies in the BX‐13 treatment was higher than that of the R. erythropolis treatment from day 10 to the end of the experiment (p < 0.05). The numbers of both BX‐13 and R. erythropolis in the water body peaked on day 15, with 2.23 × 10⁷ cfu/L and 9.90 × 10⁶ cfu/L respectively. The bioflocculation volume (BFV) in water increased and then stabilized in both BX‐13 and R. erythropolis treatments. The BFV in BX‐13 peaked on day 25 (52.13 ml/L) and R. erythropolis peaked on day 30 (22.63 ml/L). At the end of the experiment, the BFV of the BX‐13 treatment was higher than the R. erythropolis treatment (p < 0.05). In conclusion, B. subtilis BX‐13 has a very strong flocculation effect, and merits further research into its application for water quality regulation in aquaculture systems.     

Individual and spatial variation are as important as species‐level variation to the trophic complexity of a lentic food web

Ecological complexity may improve ecosystem function, stability and adaptability to natural and anthropogenic disturbances. Intraspecific trophic variation can represent a significant component of total community variation and can influence food web structure and function. Thus, understanding how trophic niches are partitioned between intraspecific and interspecific processes could improve our understanding of food web dynamics. We examined gut contents, fatty acids and stable isotope ratios in round goby (Neogobius melanostomus) and yellow perch (Perca flavescens) across six sites in Lake Michigan, USA, to determine patterns in intra‐ and interspecific trophic composition (i.e., mean gut or fatty acid composition) and diversity (i.e., the diversity of gut items or fatty acids). We also examined relationships between fatty acid diversity and gut content characteristics to understand potential mechanisms shaping individual trophic phenotypes. There was significant variation in both trophic composition and diversity among sites, and individual and spatial variation was as important to total trophic variation as species identity. Round goby that consumed dreissenid mussels had more diverse fatty acid profiles than those that consumed other benthic invertebrates, whereas yellow perch fatty acid diversity was not related to gut content composition. Our results confirm that intraspecific variation in resource use can be as important to trophic dynamics as interspecific variation, and that spatial variation in lower level food web processes or habitat may strongly structure local food web dynamics. Individual‐level examination of trophic diversity, in concert with trophic composition, could provide additional information about the resilience, function and adaptability of local food webs.     

Characterization of a γ‐aminobutyrate type A receptor‐associated protein gene,which is involved in the response of Portunus trituberculatus to CO2‐induced ocean acidification

The γ‐aminobutyrate type A receptor‐associated protein (GABARAP) is a ubiquitin‐like modifier implicated in membrane trafficking and fusion events involving the γ‐aminobutyrate type A receptor, autophagy and apoptosis. In this study, the gene encoding GABARAP was cloned from swimming crab Portunus trituberculatus (PtGABARAP) based on the expression sequence tag (EST). The full‐length cDNA of 664 bp includes a 5′ untranslated region (UTR) of 87 bp, a 3′ UTR of 223 bp with a poly(A) tail, and an open reading frame (ORF) of 354 bp encoding a polypeptide of 117 amino acids with a predicted molecular weight of 13.96 kDa. The deduced amino acid sequence shares high similarity (93%–100%) with GABARAPs from other species and includes a conserved Atg8 domain. In a phylogenetic analysis PtGABARAP clustered with GABARAPs from other species, and more widely with other GABARAP family proteins. The impact of elevated ocean acidification (OA) on P. trituberculatus behaviours was investigated, and real‐time RT‐PCR revealed that PtGABARAP expression was up‐regulated after OA exposure. Ocean acidification also caused crabs anxiety‐like behaviours, like the shoal average speed increase, preference for dark environment (scototaxis) and fast exploration. The results indicated that GABARAP might be involved in the interactions of GABA_A receptors and elevated‐CO₂ seawater.