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Amphidromous fishes engage in migration to overcome the spatial mismatch between adult and larval habitat. The torrentfish (Cheimarrichthys fosteri), an endemic New Zealand amphidromous fish and on...

While many of New Zealand’s freshwater fishes undertake larval migrations as part of their amphidromous life-history, little is known of the larval stages of these fish. Torrentfish (Cheimarrchthys fosteri), a New Zealand endemic, amphidromous, riffle specialist are particularly enigmatic; their spawning sites and behaviours are unknown, and larvae have never been collected either emigrating from freshwater or during their marine feeding phase. During summer drift sampling, we captured unidentified fish larvae emigrating downstream in the Waianakarua River, South Island, New Zealand. Based on multiple lines of evidence (meristic comparisons with adults, morphology, time of capture, and adult fish populations of the Waianakarua) we identify these larvae as torrentfish. This represents the first time torrentfish larvae have been captured or identified, laying the foundations for future studies into the early life-history and ecology of this unique and threatened fish.

Historic deforestation has deprived many river systems of their natural wood loadings. To study the effects of the loss of wood from waterways, a field trial was conducted in three small forested streams in New Zealand. The objectives were to (i) examine differences in fish assemblages among wooded pools (where wood provided cover), open pools and riffles and (ii) measure the effects of wood removal on channel morphology and fish assemblages. In the first part of the study, no significant differences were found in total fish density among the three habitats. However, total fish biomass was significantly higher in wooded pools (64% of total fish biomass) compared with open pools and riffles. Mean density and biomass of banded kokopu (Galaxias fasciatus) and mean biomass of longfin eel (Anguilla dieffenbachii) were highest in wooded pools, whereas the density and biomass of bluegill bully (Gobiomorphus hubbsi) and torrentfish (Cheimarrichthys fosteri) were highest in riffles. In the second part of the study, wood was removed from a 200-m section (treatment) in each stream, significantly reducing pool area and increasing the proportion of channel area and length in riffles. At the habitat scale, banded kokopu and large longfin eel were the two species mostly affected by wood removal. At the reach scale, banded kokopu biomass was significantly lower in the treatment sections. Although wooded pools were a small portion of total habitat, they provided important habitat for two of New Zealand's larger native fish taxa.

1. Habitat suitability criteria that fail to incorporate temporal variability in habitat preferences of stream fish may mis-represent critical habitat requirements and lead to setting of inappropriate flow targets when used in instream flow assessments. Developing suitability criteria from daytime observations alone relies on the assumption that habitat preferences are constant over the diel cycle. Few studies have tested these assumptions, particularly for small-bodied, cryptic, benthic species. 2. During summer in two gravel-bed rivers, bluegill bullies (Gobiomorphus hubbsi), torrentfish (Cheimarrichthys fosteri) and upland bullies (Gobiomorphus breviceps) exhibited strong preferences with respect to water depth, velocity and substratum size. All three species underwent a diel shift in microhabitat preference for at least two of these variables. 3. Microhabitat preferences were generally weaker when fish were active at night; bluegill bullies, upland bullies and especially torrentfish were observed over a broader range of depths, velocities and substratum sizes at night than during the day. Observations of fish in a stream simulator confirmed that bluegill bullies and torrentfish showed a preference for runs at dusk and return to riffles before dawn, but habitat preferences of upland bullies remained static across the diel cycle. 4. Diel microhabitat shifts affected the assessment of flow requirements. Instream habitat analysis of the Waipara River using separate day and night suitability criteria predicted differing amounts of habitat available at a given flow, and the relationships between fish abundance, fish density and flow. The presence of diel microhabitat shifts in stream fishes suggests that instream habitat analyses will produce more effective and defensible flow recommendations when patterns of nocturnal microhabitat preferences are known and critical habitat bottlenecks can be identified. Copyright © 2011 John Wiley & Sons, Ltd.

This study compared the longitudinal size distribution of bluegill bullies (Gobiomorphus hubbsi) from Hutt River with existing data on the size distributions of bluegill bullies and torrentfish (Cheimarrichthys fosteri) from Rakaia River, New Zealand. All populations had longitudinal trajectories that showed some increase in size with distance upstream. This increase in size appeared to primarily reflect the influence of amphidromous life styles, where juveniles diffuse upstream from the sea. However, a quantile regression analysis revealed differences in growth and migration rate between the two bluegill bully populations; bluegill bullies from Rakaia River grew at a slower rate and showed variation in migration rate within their population that was not evident in the Hutt River population. Null models were also generated for each population to test for the presence of all size classes of fish in the lower reaches of each river. Both bluegill bully populations showed a significant absence of the largest size classes in the lower reaches and the size trajectories differed significantly from the null models. This difference suggests that all individual bluegill bullies continuously move upstream throughout their lives. In comparison, the size distribution of torrentfish closely resembled the null model, indicating that some individuals did not migrate upstream to the same extent as others.

Parapercis colias (blue cod) and Cheimarrichthys fosteri (torrentfish) are two members of the family Pinguipedidae. They reside in habitats with different background levels of hydrodynamic activity and differ in their feeding ecology. The peripheral morphology of the mechanosensory lateral line system was investigated in each species. The torrentfish is the only freshwater member of this otherwise exclusively marine family. It resides in turbulent fast flowing habitats and feeds nocturnally on stream drift. Torrentfish have many superficial neuromasts and a simple unbranched canal system. In comparison the blue cod resides in sub-tidal slow flowing habitats, is a diurnal predator and has relatively few superficial neuromasts and a well-developed branching canal system. For these two species the background level of hydrodynamic activity does not appear to be the dominant selection pressure on lateral line morphology, in the case of the torrentfish in particular it is more compelling to view lateral line morphology in the light of environmental pressures that have favoured the evolution of nocturnal feeding.

Cheimarrichthys fosteri is an endemic New Zealand freshwater fish that has its closest common ancestry with the blue cod, Parapercis colias, a species found in New Zealand coastal seas. Cheimarrichthys fosteri is amphidromous, and widely distributed around New Zealand. The fact that it has marine-living juvenile has a strong impact on the species' distribution. Upstream/inland penetration in river systems is substantial, and the torrentfish reaches 700 m elevation and 289 km upstream from the sea. High elevation is typically achieved only at relatively short distances inland, whereas long inland penetration is achieved typically only in low-gradient river systems. The torrentfish is a poor climber, and explicit barriers to upstream migration, such as natural falls and the construction of dams and weirs, limit inland penetration in many river systems. Sparse distribution in some areas, particularly in eastern New Zealand may be due in part to absence or sparseness of riverine gravels. Absence from other areas, such as around Cook and Foveaux straits, the Marlborough Sounds, Fiordland and Stewart and Chatham islands, may result from oceanographic conditions that do not favour return to rivers of the marine-living juveniles. Ecological and behavioural variables relating to the marine life intervals are the predominating factors influencing distribution, and historical biogeographical influences are of minor importance.

Habitat use of eight native fish species was determined by electroshocking depth‐stratified lanes < 0.125 m, 0.125–0.25 m, 0.25–0.5 m, and 0.5–0.75 m. Two runs and two riffles were sampled in 34 rivers. Water depth, velocity, and substrate size were measured. Bluegilled bullies (Gobiomorphus hubbsi), upland bullies (G. breviceps), common bullies (G. cotidianus), longfinned eels (Anguilla dieffenbachii), and shortfinned eels (A. australis) made up over 80% of the total number and biomass of fish sampled. Overall, fish densities were highest along river margins in depths of less than 0.25 m, and higher in riffles than in runs. The fish species could be classified into four habitat guilds: a fast‐water guild that occupied central portions of riffles, an edge‐dwelling guild, an intermediate guild, and finally a guild that was ubiquitous. Minimum flow requirements based on habitat for the edge‐dwelling and fast‐water guilds would be conflicting, with one benefiting from low flows and the other from hi...

Juvenile torrentfish (Cheimarrichthys fosteri), which enter New Zealand rivers from the sea during spring through summer and into autumn, differ from post‐migratory juveniles and subadults in being tadpole‐like, with relatively longer but narrower heads and larger eyes, a highly compressed caudal region, and a spinous postero‐ventral preopercular margin; the fins appear larger. Migratory juveniles mostly lack the colour pattern of larger fish, and have extensive unpigmented areas on the margins of the dorsal and anal fins, most of the tail, and much of the pectoral fins. The condition found in post‐migratory juveniles and later growth stages develops soon after migration.

The diets and feeding periodicities of six small fish species were investigated in a New Zealand coastal stream over the diel period of 4 to 5 March 1993. Aquatic insect larvae dominated the diets of all fish except common bully, Gobiomorphus cotidianus, and longfinned eel, Anguilla diejfenbachii, which had a large proportion of ostracods in their diets. Dietary overlap was greatest between species pairs which were associated in the same microhabitats: A. dieffenbachii and bluegilled bully, G. hubbsi; torrentfish, Cheimarrichthys fosteri, and G. hubbsi; and G. cotidianus and upland bully, G. breviceps. Similar patterns in feeding periodicities existed for some of the species with associated diets; A. diejfenbachii and C. fosteri were nocturnal feeders, whereas G. hubbsi fed during daylight. Both G. cotidianus and G. breviceps were also diurnal feeders. In part, the results supported the hypothesis that species with temporal segregation of feeding are likely to have more similar dietary compositio...

Torrent fish feeding on natural prey in an artificial stream were studied under conditions of total darkness. The distance at which prey could be detected increased with size of prey, and decreased...

The diets and feeding periodicities of two small, riffle-dwelling fish, the torrentfish, Cheimarrichthys fosteri, and the bluegilled bully, Gobiomorphus hubbsi, were investigated in an unstable, braided New Zealand river from May 1985 to April 1986. Aquatic insect larvae dominated diets of all fish and dietary overlap between species was high in 10 of 12 months. Nevertheless, the relative importance of prey items, as assessed by the index of relative importance (IRI), differed between species. Gobiomorphus hubbsi fed almost exclusively on larval Deleatidium (Ephemeroptera), whereas C. fosteri consumed a greater variety of prey items, with Deleatidium and trichopteran, elmid and chironomid larvae numerically dominant. A dietary switch from Deleatidium to chironomid larvae occurred in both species during December 1985, when total and relative abundances of mayfly and other benthic macroinvertebrate larvae were severely reduced by two consecutive floods. A diel sampling programme indicated that the feeding periodicity of the two species differed: C. fosteri was a nocturnal feeder, whereas G. hubbsi exhibited a strong crepuscular peak in feeding activity. Overall, the two fish partition their food resource weakly by consuming prey items in different proportions and sizes and more strongly by utilizing the food resource at different times.

Populations of small fish were sampled in 12–20 riffles of the lower reaches of 3 braided rivers in Canterbury, New Zealand, during periods of low, stable flows. In the Ashley, which has been least affected by floods in recent years, the standing stock of fish was severalfold higher than in the Hurunui and Rakaia Rivers, which experienced large floods over much of the time, particularly the Rakaia River. Mean abundance + 1 standard deviation (S.D.) of all species combined, amounted to 5.95 + 2.76 fish m 2 for 10 species in the Ashley, 0.59 + 0.60 fish m 2 for 7 species in the Hurunui, and 0.23 + 0.11 fish m 2for 6 species in the Rakaia. Mean biomass was 24.85 + 9.59, 2.11 + 1.19, and 2.50 ± 3.60 g m 2in the Ashley, Hurunui, and Rakaia Rivers, respectively. The more common species in the Ashley and Rakaia Rivers were torrentfish, longfinned eel, blue‐gilled bully, and upland bully. The same dominant species complex prevailed in the Hurunui River except that the common river galaxias was present in...

The reproductive biology of torrentfish, Cheimarrichthys fosteri Haast, was investigated in the braided Rakaia and Ashley Rivers, South Island, New Zealand. Fish matured in their second year (1+) with males exceeding 63 mm and females 65 mm in fork length (FL). Few fish lived for more than 3 years. Spawning is thought to take place in the lower reaches of rivers and occurred in both rivers from January to April. Gonosomatic index (GI) values for females were lowest from April to August, inclusive, in fish from both rivers; they peaked in October in the Rakaia and in January in the Ashley River. Male GI values were lowest during April‐July and highest in October and March in the Rakaia and Ashley Rivers, respectively. Fecundity varied from 2769 to 55100 eggs and was linearly related to fish length. Juveniles (0+), 23–30 mm FL, entered the Rakaia lagoon primarily from April to September. Females dispersed up stream, up to 90 km from the sea, whereas males were most abundant in the lower reaches. Th...

Torrentfish Cheimarrichthys fosteri Haast were collected at 4‐hour intervals over a full day in winter and summer, 1984–85, from the Ashley and Rakaia Rivers in Canterbury, New Zealand, to determine their diel feeding periodicity. Both populations fed, almost exclusively, from dusk to dawn in both seasons, with the quantity of food in their stomachs accumulating to peak levels by early morning. However, Ashley females had significantly less food in their stomachs than did males in summer, the season with a high incidence (91%) of females in spawning condition. Aquatic stages of Deleatidium spp. (Ephemeroptera: Leptophle‐biidae) and Chironomidae constituted from 85 to 98% by number and 63 to 80% by dry weight of all foods eaten. Chironomids (small prey) comprised up to 85% of the total foods eaten by number but only 17% by dry weight, while Deleatidium (large prey) comprised up to 69% of the prey by number and 63% by dry weight. Numerically, chironomids were an important component in the torrentfi...

Nine native diadrornous and 2 exotic fish species were recorded in an intensive survey of tributaries of the Mokau River. At the site level, species diversity was low and much of the fauna had a very restricted distribution. Sites were grouped on the basis of their species composition using the classification procedure 2‐way indicator species analysis. Four groups of sites were identified, characterised by: (1) a longfinned eel‐elver assemblage; (2) a longfinned eel‐adult redfinned bully assemblage; (3) an inanga‐adult redfinned bully assemblage; and (4) a torrentfish‐bluegilled bully‐redfinned bully‐elver assemblage. Relationships between fish assemblage distribution patterns and environmental factors were examined with multiple discriminant analysis. The overriding feature influencing patterns of fish distribution was the prevalence of diadromy in the fauna with species varying in their ability to penetrate upstream. Distance from the sea and gradient from the river mouth were the environmental...

Two new trematode species, Deretrema philippae and Coitocaecum zealandicum, are described from New Zealand freshwater fishes. Deretrema philippae (from Galaxias divergens Stokell, 1959) is atypical of the genus in the lack of a prepharynx but closely resembles the genus in other respects. It is similar to D. minutum Manter, 1954, but D. minutum differs in the smaller size, presence of a prepharynx, anterior spination and fewer vitelline follicles. Both species are similar in their oocurrence in freshwater fishes. Coitocaecum, zealandicum (from Cheimarrichthys forsteri Haast, 1874) closely resembles C. gymnophallum Nicoll, 1915 and C. glandulosum Yamaguti, 1934 but differs from the former in the shape of the cirrus sac, the larger vitelline reservoir, and less anterior extension of the vitelline follicles; it differs from the latter in the absence of glands in the neck region.

The diets of two size classes of torrentfish (Cheimarrichthys fosteri Haast), taken from the Ashley River, North Canterbury, over two days in February‐March 1984, were examined. Small fish (fork length 51–64 mm) fed mainly on larval Elmi‐dae (Hydora sp.) and Chironomidae, whereas the diets of larger (71–109 mm) fish were dominated by Elmidae and Ephemeroptera (Deleatidium sp.) larvae. Aquatic larvae dominated diets of all fish; only one item of terrestrial origin was recorded. Torrentfish consumed proportionally greater numbers of slow than fast moving prey. The size range of most prey species taken was narrower than the range present in the river. Increasing fish length did not result in an increased variety of prey items consumed by C. fosteri.

Osteological study shows that Cheimarrichthys fosteri Haast, is very closely related to the mugiloidid Parapercis colias (Bloch and Schneider). As a result, Cheimarrichthys should be placed in the family Mugiloididae. C. fosteri is described and knowledge of its biology discussed and reviewed.