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The diets and feeding ecology of larval fishes in Wilson Inlet, southwestern Australia

Gaughan, Daniel J (1992) The diets and feeding ecology of larval fishes in Wilson Inlet, southwestern Australia. PhD thesis, Murdoch University.

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Fish larvae and zooplankton were sampled at four sites in Wilson Inlet in twelve consecutive months. The annual mean concentration of fish larvae was less than one individual m^-3, whereas that of zooplankton was 447 000 individuals m^-3. The zooplankton assemblage was dominated by various life cycle stages of copepods (51.8% of the total catch), in particular their nauplii, and by tintinnid protozoans (29.8%). Copepod nauplii and Tintinnopsis sp. contributed 32.9 and 17.9 %., respectively, to the mean annual catch of zooplankton. The larvae of 10 species of fish were caught, of which six (Pseudogobius olorum, Afurcagobius suppositus, Favonigobius lateralis, Urocampus carinirostris, Parablennius tasmanianus and Engraulis australis) were common and four (Leptatherina presbyter aides, Atherinosoma elongata, Platycephalus speculator and Hyporhamphus melanochir) were rare. The guts of only the first five of the above six abundant species regularly contained food.

Overall, the relative composition of the diets of the larval fishes and the relative composition of the zooplankton were significantly (p < 0.01) correlated. The composition of the diets of P. olorum, F. lateralis, and P. tasmanianus were also usually positively correlated with the composition of the zooplankton, both on an overall basis and at individual sites within particular months. This did not apply, however, to A. suppositus and U. carinirostris. The nauplii, copepodites and adults of three species of copepods, namely Oithona simplex, Gladioferens imparipes and Acartia cf. simplex, contributed 76% of the total number, and 83% of the total volume, of prey eaten. Other important prey types were harpacticoids, bivalve larvae, polychaete larvae and the rotifer Synchaeta cf. baltica.

The assemblage of larval fishes within Wilson Inlet significantly (p < 0.05) selected only copepod nauplii in terms of numbers, and only O. simplex and G. imparipes with respect to volume. Copepod nauplii were usually positively selected only by P. tasmanianus and F. lateralis. In contrast, A. suppositus typically selected against copepod nauplii, but positively selected G. imparipes and harpacticoids. Pseudogobius olorum and U. carinirostris were the only species which often selected O. simplex, and the former also usually selected against copepod nauplii. Although relatively few prey types contributed to the diets of the fish larvae, the larvae of different species consumed different proportions of the available zooplankton, and this was reflected by the presence of significant dietary guild structure.

The larval fishes in Wilson Inlet consumed on average 0.33% of the standing crop of zooplankton in their region per day. This moderately low rate of consumption suggests that there was an excess of zooplanktonic food available for the fish larvae in Wilson Inlet and that they probably had little impact on the zooplankton populations. Despite the apparently abundant food supply, the larval fishes partitioned the food resources, which would minimize any potential for competition.

Item Type: Thesis (PhD)
Murdoch Affiliation: School of Mathematical and Physical Sciences
Notes: Note to the author: If you would like to make your thesis openly available on Murdoch University Library's Research Repository, please contact: Thank you.
Supervisor(s): Potter, Ian
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