Parasites as indicators of movement and population connectivity of a non‐diadromous, tropical estuarine teleost: king threadfin Polydactylus macrochir

Abstract

Temporal and spatial patterns in parasite assemblages were examined to evaluate the degree of movement and connectivity of post-recruitment life-history stages of a large, non-diadromous tropical estuarine teleost, king threadfin Polydactylus macrochir, collected from 18 locations across northern Australia. Ten parasites types (juvenile stages of two nematodes and seven cestodes, and adults of an acanthocephalan) were deemed to be suitable for use as biological tags, in that they were considered to have a long residence time in the fish, were relatively easy to find and were morphologically very different to each other which aided discrimination. Univariate and discriminant function analysis of these parasites revealed little difference in temporal replicates collected from five locations, suggesting that the parasite communities were stable over the timeframes explored. Univariate, discriminant function, and Bray-Curtis similarity analyses indicated significant spatial heterogeneity, with Bray-Curtis classification accuracies ranging from 55 to 100% for locations in north-western and northern Australia, 24 to 88% in the Gulf of Carpentaria, and 39 to 88% on the east coast of Queensland. Few differences were observed among locations separated by<200 km. The observed patterns of parasite infection are in agreement with concurrent studies of movement and connectivity of P. macrochir in that they indicate a complex population structure across northern Australia. These results should be considered when reviewing the management arrangements for this species.

Parasites as valuable stock markers for fisheries in Australasia, East Asia and the Pacific Islands

“…The numbers of trypanorhynch metacestodes are generally positively correlated with fish age (e.g. Lester et al 2001; Moore et al 2011, 2012 a ) suggesting that long survival of metacestodes in fish may be a common phenomenon. One exception is Hepatoxylon trichiuri in albacore, Thunnus alalunga , which may not survive for the life of the fish (Jones, 1991).…”

“…Using many of the same parasite types, Moore et al (2012 a ) examined 990 individual P. macrochir among 18 locations across northern Australia, as part of a multidisciplinary study into the movement and stock structure of the species. They found that while fish from most locations generally harboured different parasite faunas, suggesting the existence of a mosaic of stocks across northern Australia, fish from the south-eastern Gulf of Carpentaria were found to share a similar parasite fauna over spatial scales of up to 500 km.…”

“…This was in agreement with results from Newman et al (2010 b ), Horne et al (2012) and Moore et al (2012 b ) who found no significant difference in whole otolith stable isotope ratios, mtDNA signatures and life-history parameters, respectively, among fish over a similar range. The presence of a distinct stock in the Gulf of Carpentaria was further emphasized by significant age truncation and reduced length and age at sex change compared with other areas and compared with samples collected at the same location 10–15 years ago, presumably the result of overfishing (Moore, 2011).…”

“…Thus comparisons between areas can be misleading unless fish age is taken into account, such as by restricting analysis to fish within a specified age group, or adjusting parasite numbers for fish age or a suitable proxy for age such as otolith weight (e.g. Lester et al 2001; Moore et al 2011; Moore et al 2012 a ). Due to the asymptotic nature of growth frequently observed in fishes, lengths are generally a poor proxy for age, and should be used only when other types of data are unavailable.…”

Acanthocephalan Cystacanths from Flatfish (Order Pleuronectiformes) in Tropical Australian Waters

“…Neoechinorhynchus topseyi Podder, 1937, now identified as N. vittiformis Smales, 2013, and Raosentis sp. were reported from Eleutheronema tetradactylum (Shaw), although whether they were collected in both the eastern coast of Queensland and the Gulf of Carpentaria was not indicated (Moore et al, 2012, Smales, 2013. In addition, 2 species have been reported from the Gulf of Carpentaria.…”