Galaxias Maculatus Research Articles

Social and metabolic mediation of growth performance in a temperate estuarine fish

Despite the importance of juvenile growth to lifetime fitness, high variability exists within many fish species where some individuals grow markedly faster than others. Here, we explored whether social context mediated growth performance in n = 35 Galaxias maculatus by manipulating the social environment after identifying different growth phenotypes. We found that initially fast-growing fish slowed their growth rate when pooled with similarly fast-growing individuals, whereas none of the initially slow-growing fish markedly improved their growth when pooled with other slow-growers. We examined for any metabolic underpinnings to the findings by measuring standard, routine, and maximum metabolic rates (SMR, RMR, and MMR) at two time points separated by ~4 months. SMR and RMR positively correlated with growth rates when the fish were pooled into growth phenotypes, but not when they were returned to their original (mixed) social groups. We highlight research directions to further elucidate how social context and metabolism interact to govern growth phenotype.

Cryptic diversity within two widespread diadromous freshwater fishes (Teleostei: Galaxiidae).

Identification of taxonomically cryptic species is essential for the effective conservation of biodiversity. Freshwater-limited organisms tend to be genetically isolated by drainage boundaries, and thus may be expected to show substantial cryptic phylogenetic and taxonomic diversity. By comparison, populations of diadromous taxa, that migrate between freshwater and marine environments, are expected to show less genetic differentiation. Here we test for cryptic diversity in Australasian populations (both diadromous and non-diadromous) of two widespread Southern Hemisphere fish species, Galaxias brevipinnis and Galaxias maculatus. Both mtDNA and nuclear markers reveal putative cryptic species within these taxa. The substantial diversity detected within G. brevipinnis may be explained by its strong climbing ability which allows it to form isolated inland populations. In island populations, G. brevipinnis similarly show deeper genetic divergence than those of G. maculatus, which may be explained by the greater abundance of G. maculatus larvae in the sea allowing more ongoing dispersal. Our study highlights that even widespread, 'high-dispersal' species can harbour substantial cryptic diversity and therefore warrant increased taxonomic and conservation attention.

Evolution of the ecological niche behind the largest disjunct freshwater fish distribution in the world.

Ecological processes that are behind distributions of species that inhabit isolated localities, complex disjunct distributions, remain poorly understood. Traditionally, vicariance and dispersion have been proposed as explanatory mechanisms that drive such distributions. However, to date, our understanding of the ecological processes driving evolution of ecological niches associated with disjunct distributions remains rudimentary. Here, we propose a framework to deconstruct drivers of such distribution using World's most widespread freshwater fish Galaxias maculatus as a model and integrating marine and freshwater environments where its life cycle may occur. Specifically, we assessed ecological and historical factors (Gondwanan vicariance, marine dispersion) and potential dispersion (niche-tracking) that explain its distribution in the Southern Hemisphere. Estimated distribution was consistent with previously reported distribution and mainly driven by temperature and topography in freshwater environments and by primary productivity and nitrate in marine environments. Niche dynamics of G. maculatus provided evidence of synergy between vicariance and marine dispersion as explanatory mechanisms of its disjunct distribution, suggesting that its ecological niche was conserved since approximately 30 Ma ago. This integrated assessment of ecological niche in marine and freshwater environments serves as a generic framework that may be applied to understand processes underpinning complex distributions of diadromous species.

Fish gill surface area can keep pace with metabolic oxygen requirements across body mass and temperature

Abstract Climate warming is driving the maximum attainable size of many fish species to decrease, yet the mechanisms underlying this ‘shrinking’ phenomenon are not well understood. The gill oxygen limitation (GOL) hypothesis is perhaps the most prominent mechanistic proposition, asserting that, as fish grow, the two‐dimensional gill surface area (GSA) progressively fails to supply enough oxygen to support the continued growth of the three‐dimensional body—a process exacerbated by increased metabolism associated with warming. However, these ideas have been hotly debated owing to limited empirical understanding of how GSA develops with respect to a fish's body mass and oxygen requirements. For the first time, we addressed this knowledge gap by rearing Galaxias maculatus for 5 months at normal (15°C) and elevated (20°C) summer temperatures, with (hyperoxia) or without (normoxia) supplementary oxygen. Quantifying individual metabolic rate and GSA traits across body sizes encompassing most of the species' ontogeny, we found little evidence for a change in the proportion of GSA available per unit of metabolic rate (termed the S metric) and no improvements under hyperoxia. Importantly, at the elevated temperature where gill oxygen limitation should be most pronounced, the S metric did not change across body mass in either oxygen treatment (allometric exponents were no different from 0). These results indicate that the gills can grow in ways that support an individual's oxygen requirements, contrasting with the suggestion that size reductions of fish in response to climate warming are driven by an insurmountable geometric constraint at the gills. Read the free Plain Language Summary for this article on the Journal blog.

The Reproductive Biology of Puye (Galaxias maculatus) under Experimental Culture.

This study determines the reproductive patterns of puye (Galaxias maculatus) under culture conditions. A population of 567 wild fish was caught in the Cautín River, Chile, and held in captivity for four years. Mortality, sex ratio, gonadosomatic index (GSI), sexual maturity stages, spawning period, type and frequency of spawning, and fecundity were measured. The fish grew throughout the experimental period, with the fastest rate during the first half of the first year of life. The highest mortality occurred during the first three months of the experiment and during the spawning season. The sex ratio was almost 1:1 (female:male). First sexual maturity was reached at one year of age, with an average weight of 0.85 ± 0.01 g, total length of 4.85 ± 0.16 cm, and condition factor 0.0074. The highest GSI in both females (12.14 ± 0.74) and males (17.7 ± 2.70) was recorded in August. Nevertheless, the females spawned 3 to 10 times between September and February, with the highest reproductive peak between September and October. The number of embryos per female per day varied from 1 to 429, while the total number of embryos per female during the entire season evaluated varied from 163 to 1044. There was a high correlation (r = 0.82) between absolute fecundity and body weight. Although further studies are needed in this field, these results are basic for establishing future reproductive programs in captivity as a strategy for sustainable fisheries and aquaculture management.

High water temperature significantly influences swimming performance of New Zealand migratory species.

Anthropogenic structures in freshwater systems pose a significant threat by fragmenting habitats. Effective fish passage solutions must consider how environmental changes introduce variability into swimming performance. As temperature is considered the most important external factor influencing fish physiology, it is especially important to consider its effects on fish swimming performance. Even minor alterations in water properties, such as temperature and velocity, can profoundly affect fish metabolic demands, foraging behaviours, fitness and, consequently, swimming performance and passage success. In this study, we investigated the impact of varying water temperatures on the critical swimming speeds of four migratory New Zealand species. Our findings revealed a significant reduction in critical swimming speeds at higher water temperatures (26°C) compared to lower ones (8 and 15°C) for three out of four species (Galaxias maculatus, Galaxias brevipinnis and Gobiomorphus cotidianus). In contrast, Galaxias fasciatus exhibited no significant temperature-related changes in swimming performance, suggesting species-specific responses to temperature. The cold temperature treatment did not impact swimming performance for any of the studied species. As high water temperatures significantly reduce fish swimming performance, it is important to ensure that fish passage solutions are designed to accommodate a range of temperature changes, including spatial and temporal changes, ranging from diel to decadal fluctuations. Our research underscores the importance of incorporating temperature effects into fish passage models for habitat restoration, connectivity initiatives, and freshwater fish conservation. The influence of temperature on fish swimming performance can alter migration patterns and population dynamics, highlighting the need for adaptive conservation strategies. To ensure the resilience of freshwater ecosystems it is important to account for the impact of temperature on fish swimming performance, particularly in the context of a changing climate.

Redescription and Molecular Characterisation of Derogenes ruber Lühe, 1900 (Hemiuroidea: Derogenidae) from Chelidonichthys lastoviza (Scorpaeniformes: Triglidae) in the Western Mediterranean

PurposeDerogenes ruber Lühe, 1900, the type-species of the genus Derogenes Lühe, 1900, is a poorly known derogenid digenean. The original description of this species was not illustrated and aspects of the morphology of the parasite from the type-host remain scarce. Available records of this species were brief and/or lacked illustrations and were based on morphology alone. Additionally, molecular data for Derogenes spp. are warranted to untangle species complexes as they provide a better assessment of interspecific genetic divergence.MethodsDerogenes ruber is redescribed based on newly collected specimens from the gall bladder of its type-host Chelidonichthys lastoviza (Bonnaterre, 1788) collected in the Western Mediterranean off the Algerian coast during 2017–2019 and molecular data are provided using a partial fragment of the nuclear 28S ribosomal RNA gene (28S rRNA), the internal transcribed spacer 2 (ITS2) and a fragment of the mitochondrial cytochrome c oxidase subunit 1 (cox1) gene.ResultsWe herein provide a detailed illustrated redescription and morphometric data of D. ruber from its type-host C. lastoviza. We report a new geographical record (off Algeria) for it. Derogenes ruber is also genetically characterised for the first time. Species/lineages of Derogenes were recovered in five strongly supported reciprocally monophyletic clades: (i) D. ruber from C. lastoviza off Algeria; (ii) D. lacustris from Galaxias maculatus (Jenyns) off Argentina; (iii) Lineage “D. varicus DV1” (D. varicus sensu stricto) from fish hosts in the White and Barents seas and the North Sea; (iv) Lineage “D. varicus DV2” from mollusc hosts in the White Sea; and (v) Lineage “D. varicus DV3” from Eumicrotremus fedorovi Mandrytsa. in the Pacific Ocean. Hence, comparison of the newly generated sequences with other available data for Derogenes species supports the distinction of D. ruber confirming its taxonomic status and helping assess interspecific variation. Comparison of D. ruber with the closely related species Derogenes latus revealed overlaps in morphometric data and the validity of the latter species is questioned.ConclusionThe combination of morphological and molecular data provided for D. ruber provides a firm foundation for further investigations of Derogenes spp. Although we do describe herein material of D. ruber from the type-host, given that the occurrence of a single Derogenes species in various hosts has been challenged by molecular data, and both D. lacustris and D. varicus sensu stricto had been genetically proven to occur in various hosts, D. ruber and D. latus may be indeed synonymous. Additional sequencing effort on Derogenes spp. will strengthen systematic comparative studies and evolutionary relationships within the Derogenidae in general.

Fishways provide catchment-scale improvements to common galaxias (Galaxias maculatus) upstream of a barrier in south-eastern Australia

ABSTRACT The common occurrence of dams is a major threat to riverine fish communities globally and a common remediation technique for fragmented fish communities is fishway construction. Demonstrating the effectiveness of this technique on impacted species is required to rationalise or improve management practices. This study investigates the effects of the installation of a fishway complex on the catadromous common galaxias (Galaxias maculatus) population at a catchment scale. We used electrofishing in a before-after-control-impact design to investigate the effects of the installation of a rock-ramp and a vertical-slot fishway complex on this species. This study demonstrated an increase in the relative abundance of common galaxias of 7.6–28.1 times and a shift to higher proportions of small fish in tributaries upstream of the fishway complex (as far as 90 km upstream). These findings provide strong evidence for the efficacy of the installation of fishways to increase the number of catadromous fishes in rivers where fish migrations have been blocked by dams.

Ecological variation in invasive brown trout (Salmo trutta) within a remote coastal river catchment in northern Patagonia complicates estimates of invasion impact.

Salmonids were first introduced into the Chilean fresh waters in the 1880s, and c. 140 years later, they are ubiquitous across Chilean rivers, especially in the southern pristine fresh waters. This study examined the brown trout (Salmo trutta) and native taxa ecology in two adjacent but contrasting rivers of Chilean Patagonia. During spring 2016 and spring-fall 2017 we examined the variation in benthic macroinvertebrate and fish community composition and characterized fish size structure, stomach contents, and stable isotopes (δ13 C and δ15 N) to understand population structure, fish diet, and trophic interactions between S. trutta and native taxa. The native Galaxias maculatus (puye) dominated the fish community (74% of abundance). S. trutta was less abundant (16% of survey catch) but dominated the fish community (over 53%) in terms of biomass. S. trutta showed distinct diets (stomach content analysis) in the two rivers, and individuals from the larger river were notably more piscivorous, consuming native fish with a relatively small body size (<100-mm total length). Native fishes were isotopically distinct from S. trutta, which showed a wider isotopic niche in the smaller river, indicating that their trophic role was more variable than in the larger river (piscivorous). This study provides data from the unstudied pristine coastal rivers in Patagonia and reveals that interactions between native and introduced species can vary at very local spatial scales.

Reproductive traits in the southernmost landlocked population of the fish Galaxias maculatus

Reproductive traits in the southernmost landlocked population of the fish Galaxias maculatus

Evidence for energy reallocation, not oxygen limitation, driving the deceleration in growth of adult fish.

The lifetime growth of almost all fishes follows a biphasic relationship - juvenile growth is rapid and adult growth subsequently decelerates. For a trend that is so ubiquitous, there is no general agreement as to the underlying mechanisms causing adult growth to decelerate. Ongoing theories argue that adult growth slows because either the gills fail to supply the body with surplus oxygen needed for continued somatic gain (i.e. oxygen limited), or sexual maturation induces a switch in energy allocation towards reproduction and away from growth (i.e. energy limited). Here, we empirically tested these notions by tracking the individual growth trajectories of ∼100 female Galaxias maculatus, ranging in size, during their first 3 months of adulthood. At a summer temperature of 20°C, we provided subsets of fish with additional energy (fed once versus twice a day), supplementary oxygen (normoxia versus hyperoxia), or a combination of the two, to assess whether we could change the trajectory of adult growth. We found that growth improved marginally with additional energy, yet remained unaffected by supplementary oxygen, thereby providing evidence for a role for energy reallocation in the deceleration of adult growth. Interestingly, additional dietary energy had a disproportionately larger effect on the growth of fish that matured at a greater size, revealing size-dependent variance in energy acquisition and/or allocation budgets at summer temperatures. Overall, these findings contribute towards understanding the mechanisms driving widespread declines in the body size of fish with climate warming.

Local variation in the timing of reproduction and recruitment in a widely distributed diadromous fish

ABSTRACT Īnanga (Galaxias maculatus) is a widespread freshwater fish, found around coastal New Zealand, Chatham Islands, southern Australia and southern South America, exhibiting both diadromous and land-locked life history patterns. We assessed population size structure, size at maturity, timing of reproduction, and post-reproductive survival in the Waikouaiti and Kakanui rivers, two regionally important G. maculatus populations in southern New Zealand. Size at maturity varied between rivers and sexes, with males generally maturing at smaller sizes than females. The timing of reproduction and recruitment was observed to vary across a relatively small spatial scale. Population length-frequencies indicated that both populations exhibited annual population dynamics, with most individuals spawning in their first year, then apparently dying soon afterwards (as indicated by a marked drop in post-spawning abundance). However, a few individuals with recently spent or resting gonads were present over the winter months, indicating some post-spawning survival. There was a lower frequency of exceptionally large (putatively 1+) individuals than reported for other populations around New Zealand and elsewhere, suggesting over-winter survival following spawning varies. Based on the variation in life history characters over small spatial scales, we suggest that management of regionally important G. maculatus populations should be based on catchment level information.

Closing the life‐history loop: Density effects on fecundity and egg size of an exploited, amphidromous fish (Galaxias maculatus) in freshwater protected areas

AbstractUnderstanding how fecundity and egg size respond to density‐dependent and density‐independent processes is essential for fisheries assessments because it shows managers how exploited populations respond to fishery closures. Similarly, the extent to which density‐dependent and density‐independent processes influence fecundity and egg size in freshwater protected areas (FPAs) is important for determining their conservation potential and effectiveness as a fisheries enhancement strategy.The fecundity and egg size of 164 sexually matureGalaxias maculatusfemales collected from coastal waterways on the West Coast of New Zealand's South Island were determined from a combination of techniques. Specifically, the additive and interactive effects of density, temperature, and body size on fecundity and egg size were examined in 10G. maculatuspopulations across a density gradient mediated by fishery closures and tested for an egg size/fecundity trade‐off.There was no evidence of an egg size/fecundity trade‐off, or of negative density‐dependent effects on fecundity or egg size within FPAs. Egg size, gonadosomatic index, and water temperature were correlated with latitude.Fecundity increased with body size, but egg size did not. This highlights the importance of available forage (terrestrial‐ and stream‐based prey) forG. maculatusto maintain individual growth to increase egg production and larval export derived from no‐take FPAs.For the current network of no‐take FPAs to be more effective as a management tool, efforts should focus on the remediation of in‐stream and requisite riparian spawning habitats, the degradation of which has caused population bottlenecks for this culturally and economically important amphidromous species. The major subsidy from FPAs for theG. maculatusmetapopulation is sustainable egg production if migration to sea of the greatest possible number of larvae can be ensured.

No difference between critical and sprint swimming speeds for two galaxiid species.

Researchers have used laboratory experiments to examine how fish might be affected by anthropogenic alterations and conclude how best to adjust fish passage and culvert remediation designs in response. A common way to document swimming performance for this purpose is measuring fish critical swimming speed (Ucrit ). Nonetheless, the Ucrit protocol as defined by Brett [(1964) Journal of the Fisheries Research Board of Canada, 21, 1183-1226] may be inappropriate for studying swimming performance and determining how it relates to upstream migration in benthic fish, as they may not actively swim throughout the entire Ucrit test. An alternative method to estimate swimming performance is sprint swimming speed (Usprint ), which is suggested to be a measure of the burst speed of fish rather than maximum sustained swimming speed. The authors conducted comparative swimming performance experiments to evaluate whether Usprint can be used to compare swimming performance of benthic species to that of pelagic, actively swimming species. They measured individual swimming speeds of īnanga (Galaxias maculatus), an actively swimming pelagic species, and banded kōkopu (Galaxias fasciatus), a fish that exhibits benthic station-holding behaviour, using both the Usprint and Ucrit test. Experiments revealed that no significant statistical difference between swimming speeds was estimated using the Ucrit and Usprint test protocols for both G. maculatus and G. fasciatus. The result of this study suggests that fish swimming speeds obtained using these two methods are comparable for the species used in this study. By using Usprint for benthic-associated fish and Ucrit for pelagic fish, we may be able to compare a broader range of species' swimming abilities for use in a fish passage context.

Does the loss of diadromy imply the loss of salinity tolerance? A gene expression study with replicate nondiadromous populations of Galaxias maculatus.

The recurrent colonization of freshwater habitats and subsequent loss of diadromy is a major ecological transition that has been reported in many ancestrally diadromous fishes. Such residency is often accompanied by a loss of tolerance to seawater. The amphidromous Galaxias maculatus has repeatedly colonized freshwater streams with evidence that freshwater-resident populations exhibit stark differences in their tolerance to higher salinities. Here, we used transcriptomics to gain insight into the mechanisms contributing to reduced tolerance to higher salinities in freshwater resident populations. We conducted an acute salinity challenge (0ppt to 23-25 ppt) and measured osmoregulatory ability (muscle water content) over 48 h in three populations: diadromous, saltwater intolerant resident (Toltén), and saltwater tolerant resident (Valdivia). RNA sequencing of the gills identified genes that were differentially expressed in association with the salinity change and associated with the loss of saltwater tolerance in the Toltén population. Key genes associated with saltwater acclimation were characterized in diadromous G. maculatus individuals, some of which were also expressed in the saltwater tolerant resident population (Valdivia). We found that some of these "saltwater acclimation" genes, including the cystic fibrosis transmembrane conductance regulator gene (CFTR), were not significantly upregulated in the saltwater intolerant resident population (Toltén), suggesting a potential mechanism for the loss of tolerance to higher salinities. As the suite of differentially expressed genes in the diadromous-resident comparison differed between freshwater populations, we hypothesize that diadromy loss results in unique evolutionary trajectories due to drift, so the loss of diadromy does not necessarily lead to a loss in upper salinity tolerance.

Downstream migration of telemetry-tagged adult common galaxias (

Many migratory species are under threat globally. Management actions to conserve these species require a quantitative understanding of their life-history requirements, such as cues for migration. Migrations to spawn are a critical component of the life-cycle of diadromous fishes but are often poorly understood. Downstream migration patterns of common galaxias (Galaxias maculatus) were investigated in the Bunyip–Tarago River system, southern Australia, using passive integrated transponder technology. Fish undertook rapid (typically 1–3 days) downstream migration (up to 50 km) from the upper reaches to the lowland reaches near the estuary. Migration occurred from March to May during the known spawning period, with peak movement between late April and mid-May. Migration was also related to increased river discharge, with fish being more likely to migrate on days when flow was high compared with the previous 2 days, and a waxing moon (i.e. increasing illumination). Our results fill an important knowledge gap in the life history of this widely distributed diadromous species. Importantly, the knowledge about the likely drivers of movement can inform management actions such as providing environmental flows in austral autumn and at appropriate moon phases to trigger the downstream migration of adult common galaxias from freshwater reaches to estuarine spawning areas.

Effect of protein and lipids levels in a growth diet on adult whitebait Galaxias maculatus (Jenyns 1842).

Galaxias maculatus aquaculture objectives is to produce millions of eggs. Wild females are small (2 g), have quick sexual maturity and low mean fecundity (500 eggs/female), requiring larger fishes with higher fecundity. This study aim is to evaluate experimentally the effect of the levels of protein, lipid and dietary energy on weight increases in adults. Five independent experiments were performed at different sequential time periods at the UCT hatchery, Chile. Specimens were obtained from a) Crystalline sea return specimen catches in the Tolten estuary (4 -6 cm, 0.3-0.4 g.). b) Hatchery cultured fish. Fish were fed by hand ad libitum. In experiments 1 to 4, pelleted diets were prepared with 3 to 5 levels of protein (treatments 27 up to 57%), crumble size, three 100 L fibre ponds replicates. In experiment 5 the effect of two lipid levels (8 and 21%) was evaluated with commercial extruded Salmon Nutra Starter isoproteic crumble 1 diet at 63%, replicated in 4 ponds. The results show: A tendency to increased weight in all sizes with an increased protein level in the pelleted diet.A maximal adult growth is obtained with a diet containing a minimum of 37% crude protein, with 40% the optimal value. A higher % protein in the diet or growth in weight lower feed conversion ratio. The feed conversion ratio in the extruded diet reaches up to 0.5 and in the pelleted vary from 0.7 to 1.5. Fish 0.6 g fed with 63% protein, extruded commercial diet with two different lipid levels (8 and 21%, 20.40 and 23.84 MJ kg-1, PE/TE 0.62 and 0.71) increased weight the first month 67 and 105% each. It has been established that high-energy diets with optimal levels of protein and lipid are a good short-term solution to obtain G. maculatus of higher weight.

Machine learning based assessment of small-bodied fish tracking to evaluate spoiler baffle fish passage design

Fish passage research is important to mitigate the adverse effects of fragmented river habitats caused by waterway structures. The scale at which this research is undertaken varies from small-scale laboratory prototype studies to in-situ observations at various fish passage structures and bottlenecks. Using DeepLabCut, we introduce and evaluate a machine learning based workflow to track small-bodied fish in order to facilitate improved fish passage management. We specifically studied the behaviour and kinematics of Galaxias maculatus, a widespread diadromous Southern Hemisphere fish species. Upstream fish passage was studied in the presence of three different patches of spoiler baffles at an average water velocity of 0.4 m/s. In semi-supervised mode, the fish locations were extracted, and fish behaviour, such as swimming pathways and resting locations, was analysed based on extracted positions and recorded kinematic parameters. Individual fish behaviour and kinematic parameters were then used to assess the suitability of the three different spoiler baffle designs for enhancing fish passage. Using this technique, we were able to demonstrate where different spoiler baffle configurations resulted in significant differences in fish passage success and behaviour. For example, medium-spaced smaller baffles provided more accessible and uniform resting locations, which were required for efficient upstream passage. Results are discussed in relation to fish passage management at small instream structures.

First Report of Zoonotic Tapeworms, Dibothriocephalus latus (Linnaeus, 1758) and D. dendriticus (Nitzsch, 1824), and Other Endohelminth Parasites in Chinook Salmon, Oncorhynchus tshawytscha, in Chile

In the present study, the zoonotic tapeworms Dibothriocephalus latus and Dibothriocephalus dendriticus were identified for the first time, using morphological and molecular procedures, in a population of introduced Chinook salmon in Chile. The morphological differences observed between plerocercoids of D. latus and D. dendriticus were, respectively, a retracted and obscured scolex versus one that is always visible and only partially retracted after cold fixation; extension of frontal glands; size, types of, density of, and distribution of microtriches; and number of parenchymal longitudinal muscle bundles within 50-µm spaces. With scanning electronic microscopy, both species presented 3 types of microtriches: coniform and uncinated spinitriches, and capilliform filitriches. In the body region, D. latus presents all types of microtriches, but D. dendriticus only possessed capilliform filitriches. Multiplex PCR targeting cox1 of Diphyllobothriidae and subsequent sequence analysis allowed for confirmation of species identity. All adult Chinook salmon examined (32–60 cm total length) were infected by Dibothriocephalus spp. with a range of 15–192 plerocercoids. Plerocercoids were found in the stomach, intestine, liver, spleen, gonads, swim bladder, peritoneum, heart, and muscles. The prevalence of infected salmon, the percentage of plerocercoids, and the mean intensity of D. latus in the muscles were 3, 4, and 2 times greater than that of D. dendriticus. Histological examination of the stomach, liver, spleen, gonads, and muscle revealed the presence of 1 or more encysted or free plerocercoids. In most cases, varying degrees of chronic inflammation and low presence of neutrophils were observed. The prey consumed by Chinook salmon included the native fish, Galaxias maculatus, and unidentified fish and amphipods. Other identified endohelminths were Derogenes lacustris Tsuchida, Flores, Viozzi, Rauque, and Urabe, 2021 in the stomach, Camallanus corderoi Torres, Teuber and Miranda, 1990 in the intestine, larvae of Contracaecum sp. in the intestinal wall, and Acanthocephalus tumescens (von Linstow, 1896) in the intestine. All identified parasites are reported for the first time in Chinook salmon from Chile.

Sea to the mountains: quantifying freshwater eel and trout diet reliance on marine subsidies from upstream migrating fish

ABSTRACT Despite the Southern Hemisphere’s high proportion of endemic diadromous fish, the trophic role of upstream migrating forage fish in freshwater ecosystems remains unquantified. We combined food web δ13C and δ15N analyses with fish biomass estimates to quantify estuarine resource contribution (from the ecologically significant Waituna lagoon) to the diet and growth of the apex predators, longfin eels (Anguilla dieffenbachii) and brown trout (Salmo trutta) in Waituna Creek, Southland, Aotearoa (New Zealand) during 2019 and 2021. Our results demonstrated that exceptionally high biomasses of large predatory fishes (610–830 kg km−1) were maintained in a degraded agricultural catchment through connectivity to a near-pristine estuarine lagoon. Īnanga (Galaxias maculatus) migrating upstream from the lagoon supported 60%–80% of longfin eel and 40%–90% of brown trout biomass over the two years sampled. Mass-balance modelling suggested that large predatory fish in the Waituna Creek consume about two tonnes of migrating whitebait annually. These findings highlight the wider role of estuarine/marine subsidies in structuring New Zealand freshwater food webs and challenge the orthodoxy of ‘restoring streams from the headwaters down’. Estuarine ecosystems may be more important than headwater areas for sustaining large predatory fish, such as longfin eels, when they are food limited.