Landscape biogeography and population structuring of a facultatively amphidromous galaxiid fish, Galaxias brevipinnis

Processes responsible for population structuring across spatial and temporal scales represent key components in understanding speciation and evolution. We use a hierarchical approach to investigate the degree and mechanisms of structuring in landlocked and diadromous populations of the facultatively amphidromous fish Galaxias brevipinnis across various temporal and spatial scales in southern New Zealand. To determine long-term structuring, multiple lakes and coastal sites were compared genetically. Short-term structuring was assessed using otolith microchemistry for a subset of sites, and behavioural mechanisms driving population structuring were assessed via larval distributions. Genetic data show that lakes foster divergence of lake-developing populations from each other and from coastal stream populations, whereas there is relatively little structuring within coast or lake populations. However, otolith analyses indicate that on a shorter time scale, most larvae do not disperse, i.e. recruitment is local. Thus, lake and coastal populations show a distinct meta-population structure based on catchment, in contrast to the prevailing assumption of widespread dispersal, with implications for management. Most larvae were distributed in river plumes, suggesting that a simple larval behavioural mechanism, e.g. positive rheotaxis, may result in larval retention within catchments and lakes. However, not all larvae were retained in plumes, creating opportunities for genetic exchange within-lake or among coastal sites. Genetic divergence of lake populations as a consequence of landscape and behaviour provides an insight into the potential of G. brevipinnis to diversify and speciate, when landscape and circumstances align, and also has implications for the management of this and other facultatively amphidromous species.

Morphometric and genetic variations of species composers of nike fish assemblages in Gorontalo Bay Waters, Indonesia

Sahami FM, Kepel RC, Olii AH, Pratasik SB, Lasabuda R, Wantasen A, Habibie SA. 2020. Morphometric and genetic variations of species composers of nike fish assemblages in Gorontalo Bay Waters, Indonesia. Biodiversitas 21: 4571-4581. Nike is Gobioidei fish at the post-larval and juvenile stages whose habitat is still in seawater before they migrate to the freshwater, grow up, and spawn to fulfill their life cycle as an amphidromous species. This study aims to identify the species composers of Nike fish in Gorontalo Bay waters based on their morphometric and molecular characters. 2,523 samples were collected from the catches of fishermen during three periods of their appearance in Gorontalo Bay waters from January to March 2019. The samples were grouped based on their similarity of melanophore patterns, and morphometric characters of 10 units were then measured. This study found 20 different groups of melanophore patterns; 15 of them were new melanophore patterns. DNA samples from each group of new melanophore patterns were then isolated for molecular analysis. The morphometric analysis grouped the 20 melanophore patterns into three separate clusters that were confirmed through molecular analysis. The results of Gen Cytochrome Oxidase I (COI) sequences indicate that the new melanophore patterns of Nike fish assemblages consisting of six species; five species in the Gobiidae family (i.e. Sicyopterus parvei, S. cynocephalus, S. longifilis, S. lagocephalus, and Stiphodon semoni) and a species in the Eleotridae family (Belobranchus belobranchus).

New records of the Mountain Mullet, Dajaus monticola (Bancroft, 1834), and an overview of historical records in Texas

Dajaus monticola (Bancroft, 1834) is an amphidromous species of mugilid known from South and Central America and the islands of the Caribbean but is rarely collected in Gulf coast states of the United States. Two new records of D. monticola collected from the Gulf of Mexico (Brazoria Co.) and the Brazos River (Washington Co.) are reported from Texas. The rare occurrence of D. monticola in Texas is discussed and diagnostic characters used to distinguish this species from other mugilids found in Texas are reevaluated.

Ontogenetic shifts in habitat use during the dry season by an amphidromous shrimp in a tropical lowland river

Caridean shrimp have considerable effects on ecosystem processes and, thus, understanding their use of key habitats is important for determining their potential ecological effect. The present study examined the meso-habitat use of Macrobrachium spinipes, a large-bodied and important amphidromous species, in the Daly River, northern Australia. We examined shrimp abundance at four common meso-habitat types; sand bank, rock bars, undercut and structurally complex banks and mid-channel areas at five sites on three occasions during the dry season (May to October). We found that habitat use changed considerably first, with ontogeny, and, second, with the colonisation of habitats with algae and macrophytes as the dry season progressed. As juveniles, their habitat use was strongly associated with well structured bank environments early in the dry season. By the mid-dry season, juveniles were more abundant within sand habitats recently colonised with macrophytes and filamentous algae. Females showed little change in habitat use, whereas large-bodied dominant males generally favoured rock bars and heavily structured bank environments. The present study has provided significant insights into the changes in use of key riverine habitats throughout the dry season by an ecologically important species. This information will be of considerable value to the determination of environmental flow requirements and food-web investigations.

Australian diadromous fishes – challenges and solutions for understanding migrations in the 21st century

Diadromous fishes are a frequent but poorly understood component of coastal riverine fish communities in Australia. There are ~33 diadromous fishes found in Australian waters, mainly catadromous and amphidromous species. An extensive review of the literature identified major information gaps about the lifecycles and ecology of many of these species, with information on facultative diadromy, navigation, marine and early life stages being particularly limited. In many cases, this lack of information has led to poor management decisions and consequently many of the Australian diadromous species are under increasing threat from a range of environmental impacts. Much of the required information is difficult to obtain with traditional field surveys and, as a result, new and improved research tools and technologies, including telemetry, otolith chemistry, stable-isotope analysis (SIA) and functional magnetic resonance imaging (fMRI) are increasingly being applied. Key areas for research on Australian diadromous fishes should involve: (1) use of telemetry and otolith chemistry to determine the level of facultative diadromy and variation in diadromous movements across a species range; (2) use of otolith chemistry and SIA to gain a greater understanding of larval and juvenile marine life stages of catadromous and amphidromous species; and (3) use of fMRI or traditional techniques such as electroolfactogram (EOG) to determine the role of olfaction in spawning and migration, and the impact of impoundments and agricultural run-off on these critical life history stages.

Illustrated checklist of fishes from the Shubuto River System, southwestern Hokkaido, Japan

A checklist of fish fauna, comprising 40 species representing 15 families and 9 orders, was compiled from field, museum, and literature surveys of the Shubuto River System, southwestern Hokkaido, Japan. This area approximates the boundary of southern/northern affinities of Japanese freshwater fishes. All primary freshwater species, are listed except for Gymnogobius castaneus and all anadromous and marine amphidromous species that are scientifically presumed to occur naturally in the area. The list contains two invasive exotic species, Cyprinus carpio and Oncorhynchus mykiss, and two Siberian primary freshwater species, Lefua nikkonis and Barbatula toni, which are thought to mark the boundary of southern and northern affinities of Japanese freshwater fishes. Rhynchocypris perenurus, another Siberian primary freshwater species with a similar presumed range, was not recorded. The voucher specimen species included Platycephalus sp. 2, which is suggested to have the northernmost extended range.

Comparative larval development of three amphidromous Rhinogobius species, making reference to their habitat preferences and migration biology

Eggs and larvae of three amphidromous species of Rhinogobius goby (Rhinogobius brunneus, Rhinogobius sp. MO and Rhinogobius sp. CB) from Okinawa Island, Japan, were reared under uniform conditions to describe and compare their larval development. Although the larval morphologies of the three species were very similar, some differences were observed in the timing of ontogenetic events among them. R. brunneus had the largest yolk and saved it for a longer period of time, whereas Rhinogobius sp. MO had the smallest yolk, which was exhausted earlier. The period until yolk exhaustion is thought to restrict the distance that migrating larvae can drift, which determines the specific adult distribution. Each of these two amphidromous species are close relatives of different fluvial resident species. Evolution of the fluvial residents could be explained by different scenarios based on the larval traits of R. brunneus and Rhinogobius sp. MO. Rhinogobius sp. CB hatched at a smaller size and grew slower than the other two species. No fluvial species have derived from Rhinogobius sp. CB. One possible explanation is that the smaller and slower-growing larvae of Rhinogobius sp. CB find it more difficult to remain within streams.