First maturity and spawning periodicity of hatchery‐origin pallid sturgeon in the upper Missouri River above Fort Peck Reservoir,Montana

The pallid sturgeon Scaphirhynchus albus conservation propagation program has augmented declining wild populations since the 1990s and the older age classes of hatchery‐origin fish are beginning to reach sexual maturity in the wild. Currently, the majority of the information available on the age and size at first maturity and spawning periodicity for pallid sturgeon in the upper basin is from captive hatchery‐origin pallid sturgeon (i.e. age and size at first maturity and spawning periodicity) or from wild pallid sturgeon artificially spawned in the propagation program (i.e. spawning periodicity). The purpose of this study was to document age and size at first maturity and spawning periodicity of known age hatchery‐origin pallid sturgeon that have reached maturity in the wild. Radio‐tagged pallid sturgeon in the upper Missouri River upstream of Fort Peck Reservoir were serially sampled in the early‐spring over multiple years and assigned to reproductive classifications each year based on sex‐steroid concentrations. The youngest reproductively‐active male hatchery‐origin pallid sturgeon sampled was 14.5 years old and the youngest female was 18. Hatchery‐origin males were observed having annual (N = 3) and biennial (N = 2) reproductive cycles. The observed spawning periodicity was similar to what has been reported elsewhere for the species. The youngest mature fish in this study are older and larger than what has been reported for those retained in captivity, indicating that body size alone is not a reliable predictor of maturity for pallid sturgeon.     

Silver spoons in the rough: can environmental enrichment improve survival of hatchery Atlantic salmon Salmo salar in the wild?

This study tested the ‘silver spoon’ hypothesis which posits that individuals that develop under favourable conditions should enjoy a fitness advantage later in life because they are more likely to recognize and settle in high‐quality habitats. Atlantic salmon Salmo salar of two age classes (0+ and 1+ years) were reared in environmentally enriched or standard hatchery tanks for a short period (c. 10 weeks), were then released into a natural river and sampled on repeated occasions to test for silver‐spoon effects. Compared with controls, enriched fish had a 6·4% higher recapture rate and settled in higher velocity habitats when they were stocked as 0+ year fry, but not when they were stocked as 1+ year parr. The opportunity for selection was generally higher for environmentally enriched fish than for controls, and also higher for 0+ than for 1+ year fish. Selection favoured individuals with high condition factor, extensive fat reserves and longer than average pectoral fins in both age classes but favoured a small body size in 1+ year and a large body size in 0+ year releases. Stomach analysis showed that enriched fish ate more, and adapted quicker to natural prey than controls. These results provide support for silver‐spoon effects in fish and indicate that enrichment can improve post‐release performance in conservation programmes, but seemingly only if fish are not kept in captivity for too long.     

Effects of hatchery rearing on Florida largemouth bass Micropterus floridanus resource allocation and performance under semi‐natural conditions

This study examined the growth, activity, metabolism and post‐release survival of three groups of Florida largemouth bass Micropterus floridanus: wild‐caught fish, hatchery fish reared according to standard practice (hatchery standard) and hatchery fish reared under reduced and unpredictable food provisioning (hatchery manipulated). Hatchery‐standard fish differed from wild‐caught fish in all measured variables, including survival in semi‐natural ponds. Hatchery‐standard and hatchery‐manipulated fish showed higher activity levels, faster growth and lower standard metabolic rates than wild‐caught fish in the hatchery. Fish reared under the manipulated feeding regime showed increased metabolic rates and increased post‐release growth, similar to wild‐caught fish. Their activity levels and post‐release survival, however, remained similar to those of hatchery‐standard fish. Activity was negatively correlated with post‐release survival and failure of the feed manipulation to reduce activity may have contributed to its failure to improve post‐release survival. Activity and post‐release survival may be influenced by characteristics of the rearing environment other than the feeding regime, such as stock density or water flow rates.     

Morphological plasticity in a native freshwater fish from semiarid Australia in response to variable water flows

In fishes, alterations to the natural flow regime are associated with divergence in body shape morphology compared with individuals from unaltered habitats. However, it is unclear whether this morphological divergence is attributable to evolutionary responses to modified flows, or is a result of phenotypic plasticity. Fishes inhabiting arid regions are ideal candidates for studying morphological plasticity as they are frequently exposed to extreme natural hydrological variability. We examined the effect of early exposure to flows on the development of body shape morphology in the western rainbowfish (Melanotaenia australis), a freshwater fish that is native to semiarid northwest Australia. Wild fish were collected from a region (the Hamersley Ranges) where fish in some habitats are subject to altered water flows due to mining activity. The offspring of wild‐caught fish were reared in replicated fast‐flow or slow‐flow channels, and geometric morphometric analyses were used to evaluate variation in fish body shape following 3, 6, 9, and 12 months of exposure. Water flows influenced fish morphology after 6 and 9 months of flow exposure, with fish in fast‐flow environments displaying a more robust body shape than those in slow‐flow habitats. No effect of flow exposure was observed at 3 and 12 months. Fishes also showed significant morphological variation within flow treatments, perhaps due to subtle differences in water flow among the replicate channels. Our findings suggest that early exposure to water flows can induce shifts in body shape morphology in arid zone freshwater fishes. Morphological plasticity may act to buffer arid zone populations from the impacts of anthropogenic activities, but further studies are required to link body shape plasticity with behavioral performance in habitats with modified flows.     

Radio‐telemetry shows differences in the behaviour of wild and hatchery‐reared European grayling Thymallus thymallus in response to environmental variables

Juvenile wild and hatchery‐reared European grayling Thymallus thymallus were tagged with radio‐transmitters and tracked in the Blanice River, River Elbe catchment, Czech Republic, to study their behavioural response to stocking and environmental variation. Both wild and hatchery‐reared T. thymallus increased their diel movements and home range with increasing light intensity, flow, temperature and turbidity, but the characteristics of their responses differed. Environmental variables influenced the movement of wild T. thymallus up to a specific threshold, whereas no such threshold was observed in hatchery‐reared T. thymallus. Hatchery‐reared fish displayed greater total migration distance over the study period (total migration) than did wild fish, which was caused mainly by their dispersal in the downstream direction.     

Effects of captivity,diet, and relocation on the gut bacterial communities of white‐footed mice

Microbes can have important impacts on their host's survival. Captive breeding programs for endangered species include periods of captivity that can ultimately have an impact on reintroduction success. No study to date has investigated the impacts of captive diet on the gut microbiota during the relocation process of generalist species. This study simulated a captive breeding program with white‐footed mice (Peromyscus leucopus) to describe the variability in gut microbial community structure and composition during captivity and relocation in their natural habitat, and compared it to wild individuals. Mice born in captivity were fed two different diets, a control with dry standardized pellets and a treatment with nonprocessed components that reflect a version of their wild diet that could be provided in captivity. The mice from the two groups were then relocated to their natural habitat. Relocated mice that had the treatment diet had more phylotypes in common with the wild‐host microbiota than mice under the control diet or mice kept in captivity. These results have broad implications for our understanding of microbial community dynamics and the effects of captivity on reintroduced animals, including the potential impact on the survival of endangered species. This study demonstrates that ex situ conservation actions should consider a more holistic perspective of an animal's biology including its microbes.     

Interactions between endangered wild and hatchery salmonids: can the pitfalls of artificial propagation be avoided in small coastal streams?

Hatchery and wild juvenile populations of steelhead Oncorhynchus mykiss and coho salmon Oncorhynchus kisutch , in a small coastal watershed in central California, were sampled throughout the year in a stream and at a hatchery. Both species grew faster in captivity than in the wild. Hatchery fish of both species had elevated gill Na⁺, K⁺‐ATPase activity, and thus were ready to enter sea water when planted during the wild fish migration. Downstream migrant trapping and stream surveys indicated that hatchery smolts went to sea soon after planting, consequently avoiding the effects of competition and predation that commonly occur when hatchery‐bred juveniles are released. Adult steelhead were also sampled throughout the watershed. The return of hatchery steelhead was highly synchronized with that of wild steelhead, indicating that hatchery propagation had no adverse effects on the timing of the run. A disproportionate number of hatchery steelhead returned to the tributary where the hatchery was located, despite being planted throughout the watershed. Hatchery steelhead did not differ in mean age or size from wild steelhead. Observations of spawning indicated that hatchery and wild steelhead interbreed. Competition for mates or spawning substratum was rarely observed between hatchery and wild steelhead. Many of the problems commonly associated with artificial propagation can be avoided in small coastal watersheds when wild broodstock are used and fish are released as smolts.     

Reproductive seasonality in captive wild ruminants: implications for biogeographical adaptation,photoperiodic control,and life history

Many ruminant species show seasonal patterns of reproduction. Causes for this are widely debated, and include adaptations to seasonal availability of resources (with cues either from body condition in more tropical, or from photoperiodism in higher latitude habitats) and/or defence strategies against predators. Conclusions so far are limited to datasets with less than 30 species. Here, we use a dataset on 110 wild ruminant species kept in captivity in temperate‐zone zoos to describe their reproductive patterns quantitatively [determining the birth peak breadth (BPB) as the number of days in which 80% of all births occur]; then we link this pattern to various biological characteristics [latitude of origin, mother‐young‐relationship (hider/follower), proportion of grass in the natural diet (grazer/browser), sexual size dimorphism/mating system], and compare it with reports for free‐ranging animals. When comparing taxonomic subgroups, variance in BPB is highly correlated to the minimum, but not the maximum BPB, suggesting that a high BPB (i.e. an aseasonal reproductive pattern) is the plesiomorphic character in ruminants. Globally, latitude of natural origin is highly correlated to the BPB observed in captivity, supporting an overruling impact of photoperiodism on ruminant reproduction. Feeding type has no additional influence; the hider/follower dichotomy, associated with the anti‐predator strategy of ‘swamping’, has additional influence in the subset of African species only. Sexual size dimorphism and mating system are marginally associated with the BPB, potentially indicating a facilitation of polygamy under seasonal conditions. The difference in the calculated Julian date of conception between captive populations and that reported for free‐ranging ones corresponds to the one expected if absolute day length was the main trigger in highly seasonal species: calculated day length at the time of conception between free‐ranging and captive populations followed a y = x relationship. Only 11 species (all originating from lower latitudes) were considered to change their reproductive pattern distinctively between the wild and captivity, with 10 becoming less seasonal (but not aseasonal) in human care, indicating that seasonality observed in the wild was partly resource‐associated. Only one species (Antidorcas marsupialis) became more seasonal in captivity, presumably because resource availability in the wild overrules the innate photoperiodic response. Reproductive seasonality explains additional variance in the body mass–gestation period relationship, with more seasonal species having shorter gestation periods for their body size. We conclude that photoperiodism, and in particular absolute day length, are genetically fixed triggers for reproduction that may be malleable to some extent by body condition, and that plasticity in gestation length is an important facilitator that may partly explain the success of ruminant radiation to high latitudes. Evidence for an anti‐predator strategy involving seasonal reproduction is limited to African species. Reproductive seasonality following rainfall patterns may not be an adaptation to give birth in periods of high resource availability but an adaptation to allow conception only at times of good body condition.     

Strong and parallel salinity‐induced phenotypic plasticity in one generation of threespine stickleback

Phenotypic plasticity is a major factor contributing to variation of organisms in nature, yet its evolutionary significance is insufficiently understood. One example system where plasticity might have played an important role in an adaptive radiation is the threespine stickleback (Gasterosteus aculeatus), a fish that has diversified after invading freshwater lakes repeatedly from the marine habitat. The parallel phenotypic changes that occurred in this radiation were extremely rapid. This study evaluates phenotypic plasticity in stickleback body shape in response to salinity in fish stemming from a wild freshwater population. Using a split‐clutch design, we detected surprisingly large phenotypically plastic changes in body shape after one generation. Fish raised in salt water developed shallower bodies and longer jaws, and these changes were consistent and parallel across families. Although this work highlights the effect of phenotypic plasticity, we also find indications that constraints may play a role in biasing the direction of possible phenotypic change. The slopes of the allometric relationship of individual linear traits did not change across treatments, indicating that plastic change does not affect the covariation of traits with overall size. We conclude that stickleback have a large capacity for plastic phenotypic change in response to salinity and that plasticity and evolutionary constraints have likely contributed to the phenotypic diversification of these fish.     

Morphological variability of black bullhead Ameiurus melas in four non‐native European populations

External morphology in black bullhead Ameiurus melas, a fish species considered to have high invasive potential, was studied in its four non‐native European populations (British, French, Italian and Slovak). The aim of this study was to examine this species' variability in external morphology, including ontogenetic context, and to evaluate its invasive potential. Specimens from all non‐native populations reached smaller body size compared to individuals from native populations. Juvenile A. melas were found to have a relatively uniform body shape regardless of the population's origin, whereas adults developed different phenotypes depending upon location. Specimens from the U.K., Slovak and French populations appeared to be rather similar to each other, whereas the Italian population showed the most distant phenotype. This probably results from the different thermal regime in the Italian habitat. Ameiurus melas from non‐native European populations examined in this study showed some potential to alter the body shape both within and between populations. The phenotypic plasticity of A. melas, however, was not found to be as significant as in other invasive fish species. The results suggest that morphological variability itself is not necessarily essential for invasive success. The invasiveness of A. melas is therefore probably favoured by variations in its life‐history traits and reproduction variables, together with some behavioural traits (e.g. voracious feeding and parental care) rather than by phenotypic plasticity expressed in external morphology.     

Are antipredator behaviours of hatchery Salmo salar juveniles similar to wild juveniles?

This study explores how antipredator behaviour of juvenile Atlantic salmon Salmo salar developed during conventional hatchery rearing of eggs from wild brood stock, compared with the behaviour of wild‐caught juveniles from the same population. Juveniles aged 1+ years were tested in two unfamiliar environments; in one S. salar were presented with simulated predator attacks and in the other they were given the opportunity to explore an open‐field arena. No difference was found in their spontaneous escape responses or ventilation rate (reflex responses) after simulated predator attacks. Hatchery‐reared juveniles were more risk‐prone in their behaviours than wild‐caught individuals. Hatchery juveniles stayed less time in association with shelter. In the open‐field arena, hatchery juveniles were more active than wild juveniles. Hatchery juveniles were also immobile for less time and spent a shorter amount of time than wild juveniles in the fringe of the open‐field arena. Salmo salar size had no effect on the observed behaviour. Overall, this study provides empirical evidence that one generation of hatchery rearing does not change reflex responses associated with threats, whereas antipredator behaviour, typically associated with prior experience, was less developed in hatchery‐reared than in wild individuals.     

Inheritance of a darkened caudal peduncle and yellow body coloration in the gilthead sea bream (Sparus aurata L.)

This study presents data on inheritance of a darkened caudal peduncle (ebony) and yellow body coloration (yellow) in the gilthead sea bream (Sparus aurata). Fifteen progeny groups, obtained by crossing fish with three color phenotypes and of known origin, were analyzed. Analyzes of segregation in F₁ progeny involving groups from parental crosses of wild‐type colored × wild‐type colored; ebony × ebony; yellow × yellow, showed that the parents produced the offspring only with the same phenotypes (true breeding). Crosses involving F₁ wild‐type colored parents (that resulted from crosses of wild‐type parents with either ebony or yellow fish) showed in their F₂ progeny groups of which their phenotypic segregations did not differ significantly from a 3 : 1 Mendelian ratio. The progeny of back‐cross of ebony × (F₁ wild‐type colored × ebony) showed phenotypic segregations that did not differ significantly from the 1 : 1 Mendelian ratio. Overall, the results of the crossing experiments demonstrated that, similar to albinism described in a number of aquacultured species, ebony and yellow body coloration in S. aurata are both due to a single recessive allele. However, the yellow mutation of a gene controlling yellow pigment synthesis affects the yellow color of the whole fish body, whereas the ebony mutation causes production of melanin only in a specific area of the fish body, resulting in the development of a black coloration of the caudal peduncle. Experiments to assess culture performance showed that the color genes controlling ebony and yellow coloration had significant detrimental pleiotropic effects on growth, survival and body shape. Color mutations in the gilthead sea bream may be used as models for the study of: (i) genetic and physiological mechanisms of sterility, (ii) stress and disease resistance, (iii) effects of heterosis, (iv) genetic polymorphism in populations, and (v) methods of genetic protection in selected sea bream strains as well as in experiments on chromosome set manipulation.     

Patterns of morphological variation among populations of the widespread annual killifish Nothobranchius orthonotus are independent of genetic divergence and biogeography

Populations of annual killifish of the genus Nothobranchius occur in patchily distributed temporary pools in the East African savannah. Their fragmented distribution and low dispersal ability result in highly structured genetic clustering of their populations. In this study, we examined body shape variation in a widely distributed species, Nothobranchius orthonotus with known phylogeographic structure. We tested whether genetic divergence of major mitochondrial lineages forming two candidate species is congruent with phenotypic diversification, using linear and geometric morphometry analyses of body shape in 23 wild populations. We also conducted a common‐garden experiment with two wild‐derived populations to control for the effect of local environmental conditions on body shape. We identified different allometric trajectories for different mitochondrial lineages and candidate species in both sexes. However, in a principal components analysis of population‐level body shape, the separation among mitochondrial lineages was incomplete. Higher similarity of mitochondrial lineages belonging to different candidate species than that of same candidate species prevented distinction of the two candidate species on the basis of body shape. Analysis at the individual level demonstrated that N. orthonotus express high intrapopulation variability, with major overlap among individuals from all populations. In conclusion, we suggest that N. orthonotus be considered as a single species with an extensive geographic range, strong population genetic structure and high morphological variability.     

Characterizing the trophic niches of stocked and resident cyprinid fishes: consistency in partitioning over time,space and body sizes

Hatchery‐reared fish are commonly stocked into freshwaters to enhance recreational angling. As these fishes are often of high trophic position and attain relatively large sizes, they potentially interact with functionally similar resident fishes and modify food‐web structure. Hatchery‐reared barbel Barbus barbus are frequently stocked to enhance riverine cyprinid fish communities in Europe; these fish can survive for over 20 years and exceed 8 kg. Here, their trophic consequences for resident fish communities were tested using cohabitation studies, mainly involving chub Squalius cephalus, a similarly large‐bodied, omnivorous and long‐lived species. These studies were completed over three spatial scales: pond mesocosms, two streams and three lowland rivers, and used stable isotope analysis. Experiments in mesocosms over 100 days revealed rapid formation of dietary specializations and discrete trophic niches in juvenile B. barbus and S. cephalus. This niche partitioning between the species was also apparent in the streams over 2 years. In the lowland rivers, where fish were mature individuals within established populations, this pattern was also generally apparent in fishes of much larger body sizes. Thus, the stocking of these hatchery‐reared fish only incurred minor consequences for the trophic ecology of resident fish, with strong patterns of trophic niche partitioning and diet specialization. Application of these results to decision‐making frameworks should enable managers to make objective decisions on whether cyprinid fish should be stocked into lowland rivers according to ecological risk.     

Phenotypic convergence of artificially reared and wild trout is mediated by shape plasticity

Phenotypic plasticity can be viewed as the first level of defense of organism homeostasis against environmental stress and therefore represents the potential to deal with rapid environmental changes. Transitions between low complexity, artificial environments and complex, natural habitats can promote phenotypic plasticity. Here, we conducted an experimental introduction with juvenile brown trout to evaluate the plasticity of shape in response to a transition between contrasting environments. We released 202 juvenile trout reared under hatchery conditions in a natural stream and analyzed changes in shape and morphological variability after 5 months. A geometric morphometrics approach based on 14 landmarks was used to compare changes in body shape for 37 fish recaptured at the end of the experiment. A similar number of hatchery and wild fish caught at the receptor stream were used as controls for shape in the two environments. After 5‐months, fish showed significant change in shape, shifting from elongated to robust shapes, and affecting to the relative position of the caudal peduncle. These new shapes were closer to wild than to the hatchery shapes, suggesting a process of rapid phenotype change. Moreover, these changes were concomitant with a marked increase in morphological variability. Our results support the hypothesis that phenotypic plasticity is a major potential for adjustment to environmental change but not the idea that shape can be constrained by initial shapes. We confirmed the “increased” variance hypothesis and phenotype convergence with wild morphs. This has important implications because stresses the role of phenotypic plasticity as a buffer that allows organisms to cope with important environmental discontinuities at time scales that preclude the onset of adaptive adjustments. We suggest that environmental conditioning and shape plasticity can overcome both reduced morphological diversity and phenotype uncoupling with habitat characteristics resulting from initial rearing in low complexity artificial environments.     

Changes in growth rates of oral jaw elements produce evolutionary novelty in bahamian pupfish

To understand the origins of novelty and the evolution of biological diversity, it is important to investigate the processes that generate phenotypic variation from genotypic variation. A number of path‐breaking studies have revealed the genetic basis for phenotypic differences between distantly related taxa, but how qualitative change is produced during the early stages of divergence is largely unexplored. Here, we focus on striking differences in jaw morphology exhibited by three closely related sympatric pupfish species (genus Cyprinodon) from San Salvador Island, Bahamas as a basis for investigating the genetic sources of morphological variation in recently diverged species. San Salvador Island pupfish are trophically diverse and display derived jaw morphologies distinct from any other species in the genus. We illustrate these qualitative morphological differences between species with 3D‐reconstructed CT‐images and camera lucida drawings of the skulls of wild‐caught fish. Quantitative data representing the size of individual bony skull elements in wild fish show how qualitatively novel morphologies arise as a consequence of changes to the size and shape of individual skull elements, particularly the dentary, premaxilla, and maxilla bones associated with the oral jaws. Consistent with these comparative data is that the growth rate of individual bony skull elements, measured on a developmental time series of lab‐reared fish, differs between species. Our data provide a critical foundation for future studies developing San Salvador Cyprinodon pupfishes as a model system to understand the evolution and development of novel morphologies at the species level. J. Morphol. 277:935–947, 2016. © 2016 Wiley Periodicals, Inc.     

Effects of a single event of close inbreeding on growth and survival in steelhead

For two populations of Alaskan steelhead (Oncorhynchus mykiss) of common ancestry we evaluated effects of inbreeding in second-generation descendants of wild fish by comparing progeny of full-sibling matings to those of non-inbred controls to determine if a single event of close inbreeding has significant effects on survival and growth in captivity or the wild. In captivity, both survival and size were highly variable between inbred and control types within each line and among the five broods during five periods of freshwater culture. However, no consistent patterns of inbreeding enhancement or depression between types within lines across years were evident. In contrast, in the wild marine environment, 34 of 34 pairwise comparisons between inbred and control types in body size of returning adults after 2 or 3 years at liberty in the ocean were consistent with inbreeding depression with significant inbreeding depression varying from 2.9% for female length to 20.0% for female weight. Survival of marked juveniles (smolts) to adults in the wild marine environment was consistently and significantly lower in inbred types for both lines, for an average inbreeding depression of 78.8%. The results underscore the potential problems that can arise from using protective culture technologies, including captive broodstocks, to supplement endangered populations, and they highlight the genetic hazards that can be faced by small wild populations. This study demonstrates that high natural mortality or selection increases the amount of inbreeding depression detected in survival. Inbreeding effects on survival and growth in captivity can be poor indicators of survival and growth in a wild marine environment.     

Behavioural Interactions and Hormones in Naturally and Hatchery‐Spawned Chinook Salmon

Artificial breeding programmes commonly lead to domestication, which is associated with many behavioural differences that can reduce the success of animals released into natural environments. To better understand the factors contributing to domestication, we used a captive population of Chinook salmon (Oncorhynchus tshawytscha) to partition hormonal and behavioural differences to effects of the breeding method and rearing environment. We compared 9‐mo‐old juveniles from three lines that shared a common genetic background: (1) the Channel line produced by natural spawning and reared in a low‐density environment with a natural substrate for approx. 6 mo before being transferred to the hatchery; (2) the Hatchery line produced by artificial spawning; and (3) the Transfer line produced by natural spawning but reared in the hatchery from the eyed‐egg stage. Plasma concentrations of 11‐ketotestosterone (11‐KT) and cortisol were measured in groups of 150 fish and again after 4 d of social interactions in groups of six fish. There was no difference in 11‐KT among lines in large groups, but in small groups, Transfer fish had lower 11‐KT concentrations and were significantly less aggressive than both Channel and Hatchery fish. Regardless of group size, concentrations of the stress hormone cortisol were nearly twofold higher in Channel fish than in Hatchery and Transfer fish. Furthermore, the elevated cortisol concentrations in Channel fish were associated with 35% lower feeding rates than in the other two lines. Our study details complex behavioural and hormonal responses to breeding method and rearing environment in juvenile salmon.     

Linking stream ecology with morphological variability in a native freshwater fish from semi‐arid Australia

Environmental variation is a potent force affecting phenotypic expression. While freshwater fishes have provided a compelling example of the link between the environment and phenotypic diversity, few studies have been conducted with arid‐zone fishes, particularly those that occur in geographically isolated regions where species typically inhabit intermittent and ephemeral creeks. We investigated morphological variation of a freshwater fish (the western rainbowfish, Melanotaenia australis) inhabiting creeks in the Pilbara region of northwest Australia to determine whether body shape variation correlated with local environmental characteristics, including water velocity, habitat complexity, predator presence, and food availability. We expected that the geographic isolation of creeks within this arid region would result in habitat‐specific morphological specializations. We used landmark‐based geometric morphometrics to quantify the level of morphological variability in fish captured from 14 locations within three distinct subcatchments of a major river system. Western rainbowfish exhibited a range of morphologies, with variation in body depth accounting for a significant proportion (>42%) of the total variance in shape. Sexual dimorphism was also apparent, with males displaying deeper bodies than females. While the measured local habitat characteristics explained little of the observed morphological variation, fish displayed significant morphological differentiation at the level of the subcatchment. Local adaptation may partly explain the geographic patterns of body shape variation, but fine‐scale genetic studies are required to disentangle the effects of genetic differentiation from environmentally determined phenotypic plasticity in body shape. Developing a better understanding of environment–phenotype relationships in species from arid regions will provide important insights into ecological and evolutionary processes in these unique and understudied habitats.     

Maternal effects in vulnerability to eye‐parasites and correlations between behavior and parasitism in juvenile Arctic charr

Hatchery‐reared fish show high mortalities after release to the wild environment. Explanations for this include potentially predetermined genetics, behavioral, and physiological acclimation to fish farm environments, and increased vulnerability to predation and parasitism in the wild. We studied vulnerability to Diplostomum spp. parasites (load of eye flukes in the lenses), immune defense (relative spleen size) and antipredator behaviors (approaches toward predator odor, freezing, and swimming activity) in hatchery‐reared juvenile Arctic charr (Salvelinus alpinus) using a nested mating design. Fish were exposed to eye‐fluke larvae via the incoming water at the hatchery. Fish size was positively associated with parasite load, but we did not find any relationship between relative spleen size and parasitism. The offspring of different females showed significant variation in their parasite load within sires, implying a dam effect in the vulnerability to parasites. However, the family background did not have any effect on spleen size. In the mean sire level over dams, the fish from the bolder (actively swimming) families in the predator trials suffered higher loads of eye flukes than those from more cautiously behaving families. Thus, the results indicate potentially maternally inherited differences in vulnerability to eye‐fluke parasites, and that the vulnerability to parasites and behavioral activity are positively associated with each other at the sire level. This could lead to artificial and unintentional selection for increased vulnerability to both parasitism and predation if these traits are favored in fish farm environments.