Howard S. Gill

Distribution and impacts of introduced freshwater fishes in Western Australia

Abstract This paper presents comprehensive distributional data, from over 1300 sites, on introduced freshwater fishes in Western Australia. Currently, there are 10 species of introduced freshwater fish established in the inland waters of Western Australia. Most of the introduced fishes found here are those that have formed feral populations elsewhere in the world, and include members of the Salmonidae, i.e., rainbow trout (Oncorhynchus mykiss) and brown trout (Salmo trutta); Cyprinidae, i.e., goldfish (Carassius auratus) and carp (Cyprinus carpio); Poeciliidae, i.e., mosquitofish (Gambusia holbrooki), one‐spot livebearer (Phalloceros caudi‐maculatus), guppy (Poecilia reticulata), and swordtail (Xiphophorus hellerii); Percidae, i.e., redfin perch (Perca fluviatilis), and Cichlidae, i.e., Mozambique mouthbrooder or tilapia (Oreochromis mossambicus). More recently, the eastern Australian silver perch (Bidyanus bidyanus) (Terapontidae), which was introduced for aquaculture, has been captured in the Swan River near Perth. It is not known whether this population is self‐maintaining. The majority of introduced species are confined to the south‐west, although four and one species have been recorded from the Pilbara and Kimberley, respectively. Some species are extremely common and widespread, e.g., G. holbrooki and P. fluviatilis, whereas others are far more restricted and may be confined to between one and three catchments, e.g., C. carpio, P. caudimaculatus, P. reticulata, X. hellerii, O. mossambicus, and B. bidyanus. The impact of these introduced fishes on native species varies, but ranges from predation, e.g., O. mykiss, S. trutta, G. holbrooki, and P. fluviatilis, to aggressiveness, e.g., G. holbrooki, X. hellerii, and O. mossambicus, and competition for food and habitat.

Spatial segregation amongst goby species within an Australian estuary, with a comparison of the diets and salinity tolerance of the two most abundant species

The present study was undertaken to determine whether the various species of gobies that are found within the large Swan Estuary in south-western Australia are segregated within that system, and to attempt to determine the basis for any differences in their spatial distributions. The Swan Estuary comprises a long entrance channel (lower estuary), two wide basins (middle estuary) and the saline reaches of the tributary rivers (upper estuary). A total of 26232 gobies, representing seven species, was collected using a 3 mm-mesh seine net at 15 sites throughout this estuary on at least one occasion monthly over seven consecutive seasons between September 1983 and March 1985. Favonigobius lateralis and Pseudogobius olorum contributed 47.0 and 47.8%, respectively, to the total catch of gobies at all sites. The densities of each species at each site were used to determine the relative contribution of each species to the gobiid fauna at each of the sites in the lower, middle and upper estuary. Comparisons of these data with those published on the distribution and abundance of gobiid larvae confirmed that F. lateralis, which was found predominantly in the lower estuary, is a marine species that spawns in high salinities near the estuary mouth or in inshore coastal waters. In contrast, the life cycle of P. olorum and Papillogobius punctatus are typically completed within the saline reaches of the upper estuary, and that of Arenigobius bifrenatus within both this region and parts of the middle estuary where the substrate is particularly soft. Afurcagobius suppositus also spawns in this area, as well as in fresh water. Tridentiger trigonocephalus, represented by only eight individuals, is an introduced, marine species that was found mainly in the lower estuary. A single representative of the marine species Callogobius depressus was caught. The relatively low numbers of gobies caught in the middle estuary, where they contributed only about 3.5% to the total number of all gobies at all sites, may represent an aversion to the presence of rougher waters in the large basins. Circumstantial evidence suggests that the sandy substrate and consistently high salinities found in the lower estuary are preferred by F. lateralis, whereas the silty surface to the substrate and lower salinities of the upper estuary are preferred by Pseudogobius olorum. Densities of three of the four most abundant species were higher in either spring or summer than in winter, reflecting the influx of 0 + recruits, and possibly also the tendency for species in estuaries to congregate in the shallows during the warmer periods of the year. F. lateralis fed mainly on polychaetes and crustaceans, whereas P. olorum ingested predominantly algae, reflecting differences in mouth morphology and feeding behaviour, rather than the type of food available.

Distribution, biology and likely impacts of the introduced redfin perch (Perca fluviatilis) (Percidae) in Western Australia

Within Western Australia, Perca fluviatilis is restricted to the south-western corner and is found in the Swan, Murray, Harvey, Collie, Capel, Carbunup, Margaret, Blackwood, Donnelly and Warren river systems. Age data suggest it was released into Big Brook Dam (Warren River) in 1992 or 1993, where it has since played a role in eliminating the native teleosts. Its success here is attributed to a young age at maturity, rapid growth (compared with populations elsewhere), predatory nature, large size (compared with native fish), broad environmental and habitat tolerances, and absence of predators. Gonadal development initiates in late summer, with peak spawning between August and September. Males and females attained maturity in their first and second years, respectively, which is earlier than reported for most Northern Hemisphere populations and can be attributed to their rapid growth here because of the warmer climate. At ages 1, 2, 3, 4 and 5, males, on average, attained 102, 159, 206, 246 and 280 mm total length (TL) and females had attained 104, 166, 228, 290 and 351 mm TL at the respective ages. Diets of fish 50–200 mm TL comprised mainly small aquatic invertebrates, whereas larger fish preyed almost exclusively on decapods, mainly marron (Cherax tenuimanus), and teleosts.

Phylogeny of Living Parasitic Lampreys (Petromyzontiformes) Based on Morphological Data

Abstract Relationships among the 18 extant species of parasitic lamprey (Petromyzontiformes) were determined using a cladistic analysis of 32 mainly morphological characters. Because previous analyses support all known fossils as phylogenetically older or the same age as living lampreys, a composite agnathan fossil was used as an outgroup. A consensus of three equally parsimonious trees revealed a trichotomy between a monophyletic northern hemisphere clade and the southern hemisphere genera Geotria and Mordacia. The monophyletic status of the northern hemisphere lampreys and their classification in a single family Petromyzontidae was corroborated. It is suggested that the two southern hemisphere lamprey genera be retained as distinct families. Among northern hemisphere species, Ichthyomyzon and Petromyzon form a monophyletic group sister to the remaining genera. Caspiomyzon is sister to Tetrapleurodon + Entosphenus + Lethenteron + Eudontomyzon + Lampetra, with Tetrapleurodon in turn being sister to a group comprising Entosphenus and a clade containing Lethenteron and its sister group Eudontomyzon + Lampetra. Differences in many characters are related to differences in modes of feeding and behavior. In a phylogenetic context, dentitional characters are resolved as related either to blood feeding (Petromyzon, Ichthyomyzon, and Mordacia) and hypothesized to be plesiomorphic, or to flesh feeding (Eudontomyzon, Lampetra, and Geotria).

Are assemblages of black bream (Acanthopagrus butcheri) in different estuaries genetically distinct

Samples of the estuarine-spawning teleost Acanthopagrus butcheri were collected from nine estuaries and a coastal lake, located in the Pilbara and South-western drainage divisions of Western Australia and distributed along a coastline covering a distance of nearly 2,000 km. The patterns of allozyme variation in these samples were used to explore the extent to which there was variation in the genetic compositions of black bream assemblages in geographically-isolated estuarine systems, and whether or not any such variation could be related to the geographical location or type of estuary. Although only three of 36 scorable loci (Gpi-1, Ldh and Mdh-2) exhibited variation that could be used for analysis, there was considerable variation in allele frequencies at these loci among the different samples (mean FST = 0.166). Much of the detected variation was attributable to differences between the samples collected from the two drainage divisions, which are located in very different climatic regions. Furthermore, the genetic compositions of samples from neighbouring estuaries were typically more similar to each other than to those of samples collected from more distantly-located systems. However, the assemblages in one west coast and two south coast estuaries, that are closed to the ocean for extensive periods of time during the year, all showed very similar genetic compositions. Nevertheless, it is crucial to recognise that, pairwise comparisons of samples collected from the different estuaries, both within and between the two drainage divisions, almost invariably showed statistically significant differences in allele frequencies at one or more loci. Thus, our results indicate that the local populations of black bream in individual estuaries are genetically distinct, which is probably a consequence of both a limited movement by individuals between estuaries and the effects of differences in regional and local environmental conditions.

Variation in Life History of Land-Locked Lacustrine and Riverine Populations of Galaxias maculatus (Jenyns 1842) in Western Australia

Galaxias maculatus is one of the most naturally widely distributed species in the world yet there is no published literature on the biology of Western Australian populations. Galaxias maculatus in the rivers of the south coast of Western Australia inhabit an environment that is variable and at times unpredictable. By examining trends in gonadal development, lengths at first maturity, growth and appearance and persistence of larvae of G. maculatus in two saline rivers (Jerdacuttup River and Oldfield River) and one freshwater lake (Moates Lake), the life histories of populations in contrasting environments were determined. The stable conditions that prevail in the low salinity, cool waters of Moates Lake have fostered an extremely protracted breeding and larval recruitment period (year round) in comparison to limited recruitment in the riverine environments which experience less predictable flow events and water quality (salinity). An upstream migration for breeding in the Jerdacuttup and Oldfield rivers is similar to land-locked G. maculatus in south-eastern Australia and is a reversal of the downstream migration in Moates Lake or populations with marine larval dispersal, i.e. diadromous populations. Differences in population demographics existed between these habitats, with smaller maximum sizes and significantly smaller sizes at maturation occurring in the rivers compared to the lake. In Moates Lake approximately 93, 6 and 1% were 0+, 1+ and 2+, respectively; while cohort progression in the rivers suggests that most fish do not live beyond their first year. As an adaptable opportunist, G. maculatus can modify its life history strategy at a local level to persist in varied and sometimes unpredictable environments.

Biannual spawning periods and resultant divergent patterns of growth in the estuarine goby Pseudogobius olorum: temperature-induced?

Samples of juveniles and adults of the goby Pseudogobius olorum were collected from seven sites in the shallows of the upper Swan Estuary, Western Australia, using a 3 mm-mesh seine net on one or two occasions in each month between September 1983 and April 1985. The mean gonadosomatic index of female fish rose from very low values in winter (June–August) to a sharp peak in mid-spring (October), reflecting the rapid maturation of ovaries over, this period. Ovaries with post-ovulatory follicles and ovaries that were undergoing degeneration were present, in November and December, but were then either rare or absent in those members of the corresponding cohort which survived into January and February. Female fish with advanced oocytes and mature ovaries were not found in December and January, but were present in February to April. The above trends exhibited by ovarian maturity indices, together with the appearance of larvae and small fish in both spring and autumn, demonstrate that P. olorum spawns in both spring and autumn and at best to only a limited extent in summer. Length-frequency and gonadal data show that the progeny of the spring-spawning group frequently spawn in the following autumn, when they are ∼ 5 mo old, and that those of the autumn-spawning group frequently spawn in the following spring, when they are ∼ 7 mo old. Some representatives of these two spawning groups survive through the winter and summer, respectively, to breed in a second season. Growth of the progeny of the spring-spawning group was relatively rapid between late spring and mid-autumn, whereas that of the autumn-spawning group was negligible during winter, but then inceased markedly in spring. It is proposed that the biannual spawning periods in each year by P. olorum in the Swan Estuary developed as a result of a rise in water temperature over the last few thousand years. Such a rise would have brought forward further into spring and extended later into autumn the periods when the water temperatures lie within the range (20 to 25°C) at which P. olorum typically spawns. However, mid-summer is now characterised by water temperatures >25°C, which are considered less conducive to reproductive success.

Adaptive Radiation of Lampreys

Lampreys, together with hagfishes, are the sole survivors of the jawless (agnathan) stage in vertebrate evolution. The 34 species of northern hemisphere lampreys are placed in the Petromyzontidae, whereas each of the four species of southern hemisphere lampreys are separated into either the monospecific Geotriidae or monogeneric Mordaciidae. Eighteen species feed parasitically as adults in either marine or fresh waters, whereas 20 species are nonparasitic and have apparently evolved from parasitic species. This account of adaptive radiation is based on the hypothesis that the basal stock of contemporary lampreys possessed many characters that were similar to those of contemporary Ichthyomyzon and Petromyzon species, and that the Mordacia species and Geotria australis have been separated for a long period. Most of the morphological differences among the adults of northern hemisphere lampreys (i.e., variations in dentitional arrangement and size of buccal glands and velar tentacles) are related to whether the species feeds mainly on blood, as with Ichthyomyzon and Petromyzon species, or predominantly on flesh, as with the more derived Lampetra species. Mordacia species have apparently remained blood feeders, while G. australis has become a flesh feeder. The eyes of the adults of southern hemisphere lampreys are unique amongst lampreys, with those of G. australis possessing two types of cone photoreceptor (as well as a rod photoreceptor) and an irideal flap, while those of Mordacia mordax possess only a rod photoreceptor but contain a tapetum. These differences represent adaptations to life in bright surface waters by G. australis and to diurnal burrowing and nocturnal activity by Mordacia species. The restriction of larval intestinal diverticula to Mordacia species and G. australis may represent adaptations for increasing the ability to digest the particularly tough plant material that is found in southern hemisphere rivers. The bile duct of the larvae of southern hemisphere lampreys enters the apex of the above intestinal diverticula and thus, unlike the situation in northern hemisphere lampreys, does not play a role in forming the endocrine pancreas of adult lampreys during metamorphosis. This accounts for the absence of intermediate and caudal pancreatic cords in the adults of southern hemisphere species. The amino acid sequences of intestinal molecules in different lamprey taxa support the view that the lampreys are monophyletic and that polyploidy occurred early in or just prior to their evolution.

Age Composition, Growth and Reproductive Biology of the Salamanderfish Lepidogalaxias salamandroides: A Re-examination

This study has determined the age and size compositions, growth rate and reproductive biology of Lepidogalaxias salamandroides using data for fish of known sex and age and the monthly trends exhibited by various gonadal variables, including the sizes and stages of the oocytes. The results resolve conflicting conclusions drawn by other workers concerning certain aspects of the biology of this freshwater species and expands our knowledge of this teleost. Our results are based on data derived from samples collected from small, ephemeral acidic pools in south-western Australia in 22 consecutive months. Although ca. 78% of the fish caught belonged to the 0+ age class, substantial numbers of the 1+ and 2+ age classes and some 3+ and 4+ fish were caught. Spawning occurs between late May and late August, with peak activity in late July and early August. During the first year of life, growth is initially rapid, but then ceases in the weeks immediately prior to and during the period when the habitat becomes dry and fish aestivate, before recommencing in autumn as the pools again become filled with water. The growth coefficient (K) in the von Bertalanffy growth equation was lower for females (0.63) than males (1.28), reflecting the greater growth undergone by females after the first year of life. Maturity was attained by ca. 28% of the females and ca. 26% of the males that reached the end of their first year of life and by all fish that reached the end of subsequent years of life. The L50s for females and males at first maturity were 43.2 and 38.6 mm TL, respectively. The mean fecundity was only 82.4, reflecting a combination of a small body size and a relatively large egg (diameter=1.8 mm). Lepidogalaxias salamandroides is a multiple spawner, which increases the chances of some eggs and newly-hatched embryos encountering a period of favourable environmental conditions during the spawning period, which is characterised by bouts of heavy rainfall. The ratio of females to males was essentially parity in the 0+ and 1+ age classes and in all age classes collectively. When testes commence maturing for the first time, the anal fin of males starts to become modified to form a structure that facilitates the transfer of sperm to the female, and it remains modified throughout the rest of life.

Life History and Reproductive Biology of the Gilgie, Cherax Quinquecarinatus, a Freshwater Crayfish Endemic to Southwestern Australia

Abstract The gilgie, Cherax quinquecarinatus, a freshwater crayfish endemic to southwestern Western Australia, occupies a wide range of permanent and temporary aquatic environments. Reproductive and population biology parameters were determined in Bull Creek, southwestern Western Australia. Crayfish were collected monthly from May 2002 to April 2003. The seasonal von Bertalanffy growth curve, fitted for the first 14 months of life for female and male C. quinquecarinatus, had respective curvature parameters (K) and asymptotic orbital carapace lengths OCL∞ (CL∞) of 0.29 and 59.6 (71.2) mm for females and 0.25 and 73.8 (87.0) mm for males, respectively. This equates to OCLs (CLs) of females and males at age 12 months of 14.7 (19.2) and 14.1 (18.4) mm, respectively. Cherax quinquecarinatus was found to mature at a relatively small size, with the length at which 50% of individuals mature L50 for females and males being 18.8 and 24.5 mm OCL (24.1 and 30.9 mm CL), respectively. The majority of C. quinquecarinatus thus first spawned at the end of their second year of life. The potential (ovarian) and pleopodal fecundities of C. quinquecarinatus were relatively low compared to other freshwater crayfish species of similar size, being 81.7 (± 5.93 S.E.) and 77.1 (± 13.76 S.E.), respectively. Cherax quinquecarinatus underwent an extended spawning period, from late winter to late summer (i.e., August to February), with three spawning events facilitated by short brood and rapid gonadal recovery periods, traits consistent with other crayfish species able to exist in temporary environments. Estimates of total mortality (Z) were relatively high at 2.34 and 1.95/year based on age-converted catch curves for females and males, respectively, with a considerable proportion of this attributed to fishing mortality (exploitation rates of 0.76 and 0.75 for females and males, respectively). Cherax quinquecarinatus underwent a life-history strategy that showed characteristics of both a summer (r- strategist) and winter (K-strategist) brooder.