Acentrogobius pflaumii

A. pflaumii is a small gobiid that has spread through ports/harbours and estuaries of New Zealand and three Australian states. The gobiid’s cryptic nature has allowed it to become well-established without detection. It was discovered at the Victoria Docks in Port Phillip Bay, Australia in 1996 and subsequent qualitative surveys in 1996-1997 revealed that A. pflaumii occurred in almost all areas of Port Phillip Bay and also in the lower estuary of the Yarra River. Similarly, after detection in Western Australia in 2004 large populations were discovered in Cockburn Sound and the Swan River estuary. Ballast water emissions from international bulk-cargo vessels, containing eggs and/or fish, are considered the most likely introductory vector. The population increase and spread of A. pflaumii in eastern Australia and New Zealand infer that further range expansions in this region are likely.

A. pflaumii has been collected in Waitemata and Whangapoua Harbours in northeastern New Zealand (Francis et al., 2003). In Australia, it has been recorded in Botany Bay and Sydney Harbour in New South Wales (Francis et al., 2003; Rowe et al., 2008), and from Port Phillip Bay and the lower reaches of the Yarra River estuary in Victoria (Lockett and Gomon, 2001). In Western Australia, it has been collected in Cockburn Sound and the Swan River Estuary (Mead-Hunter, 2004; Maddern and Morrison, 2008).

The risk of A. pflaumii being introduced and establishing further non-indigenous populations is high. Ballast water emissions from international bulk-cargo vessels have proven effective at translocating small, cryptic gobiids (Wonham et al., 2000) including A. pflaumii (Lockett and Gomon, 2001; Francis et al., 2003). The spread of A. pflaumii in Australia and New Zealand indicates that upon introduction to suitable habitats, it can produce large populations quickly. Furthermore, based on past experiences in Australia (Victoria and Western Australia), detection of A. pflaumii is difficult if it, or at least small, cryptic, benthic fishes, are not specifically targeted or incorrect sampling techniques are used.

Within its native range, A. pflaumii occurs on soft substrata, sand and seagrass beds (Zostera spp.) in brackish estuarine waters and coastal embayments (Matsumiya et al., 1980; Kanou et al., 2004). Zostera spp. habitats are favoured by juveniles; for example Horinouchi and Sano (2001) observed A. pflaumii recruits occupying Zostera seagrass beds in Japan, and tested the effect of changes in substrate structural complexity on juvenile habitat preference and found no correlation. These authors speculated that observed juvenile densities might be determined by other factors, most notably prey availability. In contrast, the adults typically occupy open substrata.

Similar habitats are occupied by introduced populations in Australia and New Zealand. In New Zealand, A. pflaumii was collected in very shallow mud/silt substrates (i.e. by hand seine net with a drop of 1 metre) in inner harbours; some specimens were collected adjacent to Zostera capricornia beds (Francis et al., 2003). In the Yarra River estuary and Port Phillip Bay in Victoria, A. pflaumii occupies soft sediment habitats over 5 metres deep and was much rarer in shallower water (Hamer et al., 1998). The species was recorded in suitable habitats in all areas of the bay except the entrance channel (Lockett and Gomon, 2001).

In Western Australia, A. pflaumii was observed only on open, soft/silt substrata in water from 5 to 22 metres deep (Maddern and Morrison, 2008). It was not recorded on coarser, sand substrata, a preference also noted by NIMPIS (2002). Within this habitat it occupied burrows (Maddern and Morrison, 2008), a characteristic that has also been observed by Francis et al. (2003) in New Zealand and in Cockburn Sound, Western Australia (Mead-Hunter, 2004).

Genetics

The A. pflaumii diploid/haploid chromosome numbers are 50-50/25 (Froese and Pauly, 2007). See Thacker (2009) for a discussion on the molecular phylogeny of this species.

Reproductive Biology

A. pflaumii reproduces during the summer; both indigenous populations in Japan (Horinouchi and Sano, 2001) and Korea (from May to June) (Baeck et al., 2004), and introduced populations in Port Phillip Bay, Australia (NIMPIS, 2002). The eggs are often laid under dead shells (Masuda et al., 1975). The larvae are 5 – 8 mm and planktonic (Kanou et al., 2004), and the larval stage lasts approximately 30 days (Locket and Gomon, 1999). New recruits, at a mean size of 22 mm, then settle on Zostera spp. seagrass beds in autumn (Horinouchi and Sano, 2001). However, NIMPIS (2002) considers the size of recruits at settlement to be approximately 10 mm. Densities of juvenile A. pflaumii in Zostera spp. seagrass beds average one to two fish per square metre (Horinouchi and Sano, 2001). A. pflaumii matures during the first year of life in Japan (Horinouchi and Sano, 2001), and fish from Korea reproduce at approximately 4 cm (Baeck et al., 2004). Fecundity in Korean fish was size-dependent at between 3,600 and 9,700, and the proportion of female fish increased with size; i.e. 60% of all fish were female, and 100% of fish over 55 mm were female (Baeck et al., 2004).

Nutrition

A. pflaumii larvae (5 – 8 mm long) consume primarily zooplankton and copepods (Kanou et al., 2004). Benthic juveniles in Zostera spp. seagrass beds and tidal mudflats consume mainly harpacticoid copepods and gammarid amphipods (Matsumiya et al., 1980; Horinouchi and Sano, 2001; Kanou et al., 2004). The adults (about 50 mm) feed mainly on gammaridean amphipods (Matsumiya et al., 1980) and also consume mollusca, polychaetes and isopods (Kikuchi and Yamashita, 1992 in NIMPIS, 2002; Horinouchi and Sano, 2000).

Associations

In southwestern Australia, A. pflaumii co-habited burrows with alpheid shrimps. A. pflaumii was observed near the burrow entrance, while the burrow was excavated by the shrimp (Mead-Hunter, 2004; Maddern and Morrison, 2008). The shrimp is most likely Alpheus euphrosyne, which is the most abundant alepheid shrimp found in shallow water in southern Australia (Edgar, 2000). The occupation of burrows has been noted by Francis et al. (2003) in New Zealand, although the co-habitation of burrows with alepheid shrimps has been observed only in Western Australia. It is unknown if these behaviours are widespread or occur only in introduced populations and/or particular environments. However, as commented by Maddern and Morrison (2008), these behavioural characteristics may be observed only by scuba divers in situ, therefore it follows that they will only be recorded by studies utilising this sampling methodology.

Environmental Requirements

Almost no definitive data is available on the environmental tolerances of A. pflaumii. The wide geographic distribution of native and introduced populations indicates a wide temperature tolerance (from tropical/subtropical to temperate regions). Takizawa (1994) records a minimum temperature of 8°C. The water temperature in the Swan River estuary in southwestern Australia, where A. pflaumii was collected (Maddern and Morrison, 2008), varies seasonally between 13 and 24°C (M Maddern, University of Western Australia, personal observation, 2008). Notable also is that A. pflaumii will tolerate salinities from seawater to brackish water of lower estuaries (e.g. Lockett and Gomon, 2001; Maddern and Morrison, 2008). Uchida and Dotsu (1980 in NIMPIS, 2002) cite minimum (26°C) and maximum (28°C) temperatures for reproduction in captive-reared fish.

The bothid flounder, Asterorhombus intermedius, preyed upon A. pflaumii in Japan (Manabe and Shinomiya, 1998), and Froese and Pauly (2007) list Cynoglossus semilaevis (China), Sillago japonica and Sphyraena pinguis (North Korea) as predators.

General

• Research model

Small, cryptic species are, by their very nature, difficult to observe and quantify. As noted by Maddern and Morrison (2008), the ichthyofauna of the Swan River estuary has been regularly surveyed and described for at least three decades (e.g. Chubb et al., 1979; Hutchins and Thompson, 1983; Loneragan et al., 1989; Gill and Potter, 1993; Potter and Hyndes, 1999; Hoeksema and Potter, 2006) although A. pflaumii was not recorded. The techniques utilised for these surveys, mostly seine and gill nets in shallow areas (e.g. Gill and Potter, 1993; Hoeksema and Potter, 2006), and otter trawls in deeper areas (e.g. Potter and Hyndes, 1999), were inappropriate for the collection of small, cryptic fishes. Such fishes are commonly surveyed by visual censuses (e.g. Wickett and Corkum, 1998; Ray and Corkum, 2001; Johnson et al., 2005;Sapota and Skóra, 2005), and unless surveys utilising such methodologies are undertaken, cryptic species may remain undetected. Furthermore, as noted by Maddern and Morrison (2008), the behavioural characteristics of A. pflaumii in southwestern Australia (i.e. occupying burrows with alepheid shrimps) would only have been observed by scuba divers in situ, and thus would only have been recorded by studies utilising this sampling methodology.

In an Australian/New Zealand context, A. pflaumii most closely resembles Arenigobius bifrentatus. Arenigobius does not have scales on the head in advance of the dorsal fin (NIMPIS, 2002), and A. bifrentatus has different colouration, most notably angled stripes or small blotches rather than the mid-lateral blotches and iridescent blue lateral scales of A. pflaumii (Lockett and Gomon, 1999). McDowall (1996) provides a key to the identification of other endemic Australian gobies with which the streaked goby may be confused. It is important to note that as mentioned above the taxonomic status of species within Acentrogobius and related genera, including Arenigobius, are uncertain (Francis et al., 2003; H Larson, Northern Territory Museum, Australia, personal communication, 2008). Arenigobius is considered a valid genus by some researchers (e.g. Francis et al., 2003), whereas Froese and Pauly (2007) have subsumed Arenigobius into Acentrogobius.

Due to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.

Prevention

Public awareness

There is little public awareness of A. pflaumii, although review papers, such as Rowe et al. (2008) are available for public comment and will inform a wider (though admittedly mostly scientific) audience.

Eradication

There is no information on eradication/control attempts of A. pflaumii in Australia or New Zealand.

There are many knowledge gaps/research priorities: as noted in previous sections, no research has been conducted on the potential ecological impacts of A. pflaumii in Australia or New Zealand.

Australia: Fishes: Australian Museum Fish Site, Australian Museum Fish Section Division of Vertebrate Zoology 6 College Street, Sydney NSW 2010, http://www.austmus.gov.au/fishes/about/research/hoese1.htm

31/07/08 Original text by:

Mark Maddern, University of Western Australia, Australia