Larval development and dietary ontogeny of a critically endangered galaxiid within a Mediterranean climatic zone of Australia

Fiona J Rowland,Howard S Gill,Mark G Allen,David L Morgan,Stephen J Beatty,Paul G Close,Joslyn S Berkelaar,

doi:10.29094/fishmed.2017.001

Abstract

The taxonomy of critically endangered and geographically isolated populations of the Spotted Galaxias (Galaxias truttaceus) from either side of the Australian continent has only recently been resolved with those in Mediterranean-climatic Western Australia considered to be an evolutionary significant unit. Ontogenetic changes in gross morphology, pigmentation, fins and fin folds of wild-caught Galaxias truttaceus from south-western Australia are described between post-hatch and juvenile life stage. Newly hatched larvae are 5.3 mm in body lengh (BL), elongate, lightly pigmented, have well-developed eyes and mouth, a large yolk sac and straight gut. A medial unpaired fin fold extends ventro-distally from myosepta 5-8, around the ntochord and the dorso-proximally to myosepta 7-12. The commencement and completion of fin development is C, D, A -> P -> V, with the full complement of adult fin meristics present by 27 mm BL. The juvenile life stage is reached at c 34 mm BL when pigmentation and body share are consistent with those of adult stages. Larval G. trutatceus can be discriminated from other sympatric congenerics on the bases of pigmentation and position of the dorsal fin origin proximal to that of the anal fin, and from other sympatric species that are less-elongate and/or have fewer myomeres and are more heavily pigmented. A distinct ontogenetic shift in diet from aquatic to terrestrial prey occurs at transition to juvenile life stage, and presumably reflects both a change in habitat (from lentic to lotic) and the attainment of adult morphology.

Highlights

The juvenile life stage is reached at c 34 mm body length (BL) when pigmentation and body shape are consistent with those of adult stages
Larval G. truttaceus can be discriminated from other sympatric congenerics on the basis of pigmentation and the position of the dorsal fin origin proximal to that of the anal fin, and from other sympatric species that are less-elongate and/or have fewer myomeres and are more heavily pigmented
A distinct ontogenetic shift in diet from aquatic to terrestrial prey occurs at transition to juvenile life stage, and presumably reflects both a change in habitat and the attainment of adult morphology

Summary

SUMMARY

The taxonomy of critically endangered and geographically isolated populations of the Spotted Galaxias (Galaxias truttaceus) from either side of the Australian continent has only recently been resolved with those in Mediterranean-climatic Western Australia considered to be an evolutionary significant unit. Ontogenetic changes in gross morphology, pigmentation, fins and fin folds of wild-caught Galaxias truttaceus from south-western Australia are described between post-hatch and juvenile life stage. The juvenile life stage is reached at c 34 mm BL when pigmentation and body shape are consistent with those of adult stages. Larval G. truttaceus can be discriminated from other sympatric congenerics on the basis of pigmentation and the position of the dorsal fin origin proximal to that of the anal fin, and from other sympatric species that are less-elongate and/or have fewer myomeres and are more heavily pigmented. A distinct ontogenetic shift in diet from aquatic to terrestrial prey occurs at transition to juvenile life stage, and presumably reflects both a change in habitat (from lentic to lotic) and the attainment of adult morphology.

INTRODUCTION

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DISCUSSION