Tai-Sheng Chiu

Evaluating the accuracy of morphological identification of larval fishes by applying DNA barcoding.

Due to insufficient morphological diagnostic characters in larval fishes, it is easy to misidentify them and difficult to key to the genus or species level. The identification results from different laboratories are often inconsistent. This experiment aims to find out, by applying DNA barcoding, how inconsistent the identifications can be among larval fish taxonomists. One hundred morphotypes of larval fishes were chosen as test specimens. The fishes were collected with either larval fish nets or light traps in the northern, southern and northwestern waters of Taiwan. After their body lengths (SL) were measured and specimen photos were taken, all specimens were delivered, in turn, to five laboratories (A–E) in Taiwan to be identified independently. When all the results were collected, these specimens were then identified using COI barcoding. Out of a total of 100 specimens, 87 were identified to the family level, 79 to the genus level and 69 to the species level, based on the COI database currently available. The average accuracy rates of the five laboratories were quite low: 80.1% for the family level, 41.1% for the genus level, and 13.5% for the species level. If the results marked as “unidentified” were excluded from calculations, the rates went up to 75.4% and 43.7% for the genus and species levels, respectively. Thus, we suggest that larval fish identification should be more conservative; i.e., when in doubt, it is better to key only to the family and not to the genus or species level. As to the most misidentified families in our experiment, they were Sparidae, Scorpaenidae, Scombridae, Serranidae and Malacanthidae. On the other hand, Mene maculata and Microcanthus strigatus were all correctly identified to the species level because their larvae have distinct morphology. Nevertheless, barcoding remains one of the best methods to confirm species identification.

Composition and abundance of copepods and ichthyoplankton in Taiwan Strait (western North Pacific) are influenced by seasonal monsoons

Seasonal variation in hydrographic conditions in Taiwan Strait is strongly influenced by the monsoonal system. During northern winter, the China Coastal Current, pushed by the north-east (NE) monsoon, moves south- wards into Taiwan Strait and during northern summer, the South China Sea Surface Current, driven by the south-west (SW) monsoon, invades the strait until the NE monsoon again prevails. As the SW monsoon wanes (in northern autumn), the Kuroshio Branch Current enters from the southern part of the strait, but stagnates in the middle because of interference by the China Coastal Current. As the NW monsoon wanes (in northern spring), the stagnation ceases and the SW monsoon begins. We characterised zooplankton (including copepods and ichthyoplankton) communities during a period when the SW monsoon was prevalent (in August), at the onset of the NE monsoon (in November) and as the NE monsoon waned (in March). Multivariate analyses of zooplankton composition and species abun- dances demonstrated that the structures of communities are closely related to oceanic variables (such as temperature, salinity and upwelling), which, in turn, are heavily influenced by the monsoons. The zooplankton faunas in Taiwan Strait are a mixture of local species and intruding species, the latter introduced from along the China coast during northern winter and from the South China Sea during northern summer. Our findings are fundamental to practical ecosystem management and an effective long-term monitoring programme.

Trawl cod-end mesh selectivity for some fishes of North-Western Australia

Abstract A cod-end mesh selectivity experiment was conducted using the covered cod-end technique on the continental shelf of northern Australia. Cod-end (stretched) mesh sizes of 40, 51, 55, 70 and 100 mm were tested with a 30-mm-mesh cover bag. Mesh selection parameters were estimated for 28 species by fitting a logistic curve to the size-specific escapement data, and a gross selection rate was calculated for an additional 27 species. Some species (notably Lutjanus spp., Pristipomoides spp. and Plectorhynchus pictus ) were largely retained by all cod-end mesh sizes tested, while others (notably Loligo spp.) largely escaped all the cod-ends tested. The common assumption that the selection factor does not alter with mesh size was accepted for Nemipterus nematopus, Parupeneus pleurospilus and Lutjanus vittus , but rejected for Saurida undosquamis . Dependence of the selection factor upon mesh size for S. undosquamis was due to a non-zero intercept in the relationship between fish size at 50% escapement and mesh size. The general implications of dependence of selection factor on mesh size are discussed.

Microsatellite DNA markers for population‐genetic studies of blue mackerel (Scomber australasicus) and cross‐specific amplification in S. japonicus

Blue mackerel (Scomber australasicus) is targeted by large‐scale purse‐seiners in the western North Pacific, and its stock structure is still contentious. Herein, we described 10 polymorphic microsatellite loci for blue mackerel. The number of alleles among 32 individuals surveyed ranged from five to 27 (average of 16.2 alleles per locus). Departures from Hardy–Weinberg expectation were observed at two loci. Cross‐specific amplification in the congener, S. japonicus, was successful, except for one locus, revealed to be diagnostic for these congeners. These microsatellite loci will be useful tools to address queries in population genetic structure, fishery management unit and taxonomic species status in the genus Scomber.