Tissue preservation biases in stable isotopes of fishes and molluscs from Patagonian lakes

Field work commonly involves preserving samples for later use; however, most preservation methods distort stable‐isotope (SI) signatures that are of interest to ecologists. Although preservation of muscle samples with table salt and rubbing alcohol affected the SI (δ¹³C and δ¹⁵N) of important consumers in Patagonian lakes (molluscs and fishes), variation among individuals and lakes generally exceeded that among preservation treatments. Mathematical corrections for these preservation biases are provided, and a potentially bias‐free preservation by air‐drying is suggested.     

Aerial exposure tolerance of a newly discovered galaxiid

Laboratory experiments were conducted to investigate tolerance and physiological responses of Galaxias'nebula', a newly discovered and widespread African galaxiid, to aerial exposure. This species can tolerate emersion for at least 36 h. Changes in water level and dewatering did not induce the fish to burrow into the substratum or find refugia, nor was there detectable mucus production following aerial exposure. Opercular movement, a proxy for gill ventilation rate, however, did vary with changes in water level. The initial steady ventilation rate increased significantly when the fish were partially emersed and ventilation ceased immediately upon total air exposure. When fish were re-immersed, there was first a period of hyperactivity with a corresponding inflated gill ventilation rate which was restored to pretreatment levels within 2 h. This is the first documented case of amphibious capabilities in an African galaxiid, which has implications for the interpretation of its widespread distribution pattern.     

Amphibious adaptations in a newly recognized amphibious fish: Terrestrial locomotion and the influences of body size and temperature

Amphibious animals are adapted for both aquatic and terrestrial habitats. The conflicting requirements for dual habitats are perhaps most pronounced in the air‐breathing fishes, which represent an intermediate stage between the totally aquatic habitat and terrestrial colonization. A key requirement for amphibious fishes is terrestrial locomotion. The different densities and compositions of air and water impose constraints for efficient terrestrial locomotion that differ from those required for aquatic locomotion. I investigated terrestrial locomotion in a small South African fish, Galaxias ‘nebula’, by exposing 60 individual fish to air in specially designed raceways and quantifying movement type and occurrence as a function of availability of water, fish size and environmental temperature. Nebula showed a sustained undulating form of terrestrial locomotion characteristic of amphibious fishes and also a transient ballistic locomotion (jumps) typical of fully aquatic species. Terrestrial movement was influenced by fish size, with medium‐sized fish undertaking more jumps towards water, and fewer jumps away from water, than their smaller or larger conspecifics. In contrast, axial undulation was mainly influenced by temperature. However, there was no consistent pattern in temperature effects presumably because temperature is just one of a suit of environmental factors that may affect terrestrial locomotion. Nebula's amphibious adaptations allow it to cope with the unpredictability inherent in its natural environment.     

Metapopulation dynamics of a diadromous galaxiid fish and potential effects of salmonid aquaculture

1. Direct ecological effects of biological invasions have been widely documented, but indirect genetic effects on native species are poorly known. In many cases, this is because of the lack of information on the genetic structure of species affected by invasions. 2. We used microsatellite DNA loci to estimate the genetic structure and gene flow patterns of Galaxias maculatus, a galaxiid fish endemic to the southern hemisphere, which is increasingly being threatened by salmonid invasions. 3. Analysis of nine diadromous populations of G. maculatus in Chilean Patagonia (an area heavily impacted by farming of non‐native salmonids) indicates that dispersal is mostly a passive process, seemingly driven by wind and currents and resulting in high gene flow and weak population structuring. 4. Gene flow was asymmetrical, with three populations acting as sources and six populations acting as sinks. Sinks had lower habitat quality and had a greater incidence of adults than sources, which consisted mostly of juveniles. 5. Rivers invaded by salmonid escapees experienced significantly higher aquaculture pressure than rivers where salmonid escapees were apparently absent, but no effect on genetic diversity of G. maculatus could be detected. 6. We discuss whether salmonid aquaculture might affect the demography and connectivity of galaxiid metapopulations: indirectly through habitat alteration and directly through escapes of predatory fish.     

Biology of the western minnow,Galaxias occidentalis Ogilby (Teleostei : Galaxiidae), in a south-western Australian river

The size and age composition, growth and diet of the western minnow, Galaxias occidentalis, in the southern branch of the Collie River in south-western Australia were determined from samples collected at approximately monthly intervals between January 1984 and December 1986. The prominent, narrow hyaline zone on otoliths was shown to be formed annually and thus valid for ageing these fish. An examination of the otoliths of 4711 fish indicated that 69.2 and 26.8% of the fish caught belonged to the 0 + and I + age classes, respectively. While the vast majority of the remaining fish represented the II + age class, a few III + and IV + and one V + fish were also recorded. Growth was seasonal, being greatest in spring and autumn and effectively ceasing in winter. Females began to grow faster than males during their first autumn of life. The respective mean lengths of males and females were 70 and 75 mm at the end of the first year and 90 and 100 mm at the end of the second year. The largest fish caught was a III + female measuring 163 mm and weighing 32.0 g. The respective von Bertalanffy growth curve parameters for L, K and t₀ were 109, 0.758 and - 0.338 for males, and 124, 0.762 and - 0.223 for females. Although the diet of G. occidentalis was always dominated by small terrestrial fauna, and particularly insects, conspicuous seasonal differences were found between the more important of the other components. Data on body size, growth and diet of G. occidentalis are compared with those recorded for other galaxiids.     

A novel hunting method for banded kōkopu

Banded kōkopu (Galaxias fasciatus) were observed attempting to catch insects off the bank of the pool in which they lived. This is previously unrecorded behaviour for this species. Details of this behaviour were recorded and described when individuals responded to the placement of insect larvae on the bank of the pool. This behaviour could explain the differences between stomach and drift net samples in previous diet studies.     

Larval horsehair worms (Nematomorpha) from the tissues of native freshwater fish in New Zealand

Abstract

Encysted larval horsehair worms (Phylum Nematomorpha) were recovered from the tissues of upland bullies (Gobiomorphus breviceps) and a galaxiid (Galaxias vulgaris) from the Seaward River, Canterbury. The cysts were mostly in the alimentary submucosa. A few occurred in the liver. An adult digenean fluke (Coitocaecum sp.), parasitic within the gut of a bully, also contained nematomorph larvae in its tissues. It is suggested that the fish became infected by eating nematomorph larvae or egg strings.     

Across the Southern Alps by river capture? Freshwater fish phylogeography in South Island,New Zealand

We used DNA analysis of galaxiid fish to test a hypothesis of localized headwater capture in South Island, New Zealand. The restricted western, but widespread eastern, distributions of three nonmigratory freshwater fish species suggest that part of the east-flowing Waiau River has been captured by the west-flowing Buller River. However, mitochondrial control region (Kimura 2-parameter distance = 4.1-5.4%) and microsatellite flanking sequences do not support a relationship between Waiau (N = 4 fish sequences) and western populations (N = 8) of Galaxias vulgaris. Instead, the point of capture is probably to the north-east, perhaps the Nelson lakes region. Phylogenetic analysis indicates that western populations, along with populations in the north-east (N = 18), represent a previously unidentified monophyletic Evolutionarily Significant Unit, possibly a cryptic species. We suggest a general caveat for zoogeographic conclusions based on distributional data alone.     

The impact of an introduced predator on a threatened galaxiid fish is reduced by the availability of complex habitats

1. The availability of complex habitats such as macrophytes may be vital in determining the outcomes of interactions between introduced predators and native prey. Introduced brown trout (Salmo trutta) have impacted numerous small native freshwater fishes in the southern hemisphere, but the potential role of complex habitats in determining the direct outcomes of brown trout – native fish interactions has not been experimentally evaluated. 2. An in‐lake enclosure experiment was used to evaluate the importance of structurally complex habitats in affecting the direct impacts of brown trout on a threatened galaxiid fish. Five Galaxias auratus and a single brown trout were added to enclosures containing one of three different habitat types (artificial macrophytes, rocks and bare silt substrate). The experiment also had control enclosures without brown trout. Habitat‐dependence of predation risk was assessed by analysis of G. auratus losses to predation, and stomach contents of remaining fish were analysed to determine if brown trout directly affect the feeding of G. auratus and whether this is also habitat‐dependent. 3. Predation risk of G. auratus differed significantly between habitat types, with the highest mortality in enclosures with only bare silt substrate and the lowest in enclosures containing artificial macrophytes. This result highlights the importance of availability of complex habitats for trout – native fish interactions and suggests that increasing habitat degradation and loss in fresh waters may exacerbate the direct impacts of introduced predators. 4. Stomach contents analyses were restricted to fish in enclosures with artificial macrophytes and rocks, as most fish were consumed in enclosures with brown trout and only bare silt substrate. These analyses suggest that brown trout do not directly affect the feeding of G. auratus in complex habitats, but it is still unknown whether its feeding is reduced if complex habitats are unavailable.