Daily age determination and growth rates of freshwater fish throughout a regulated lotic system of the Murray‐Darling Basin Australia

Abstract

Summary To facilitate future research in freshwater fish recruitment response to environmental flow delivery, size‐at‐age and growth models are presented for eight fish species occurring in south‐eastern Australia; three small‐bodied species and the juvenile 0+ age classes of five large‐bodied species. Otolith increments were used to estimate the daily age of golden perch Macquaria ambigua, bony bream Nematalosa erebi, common carp Cyprinus carpio; Murray cod Maccullochella peelii, freshwater eel‐tailed catfish Tandanus tandanus, Australian smelt Retropinna semoni, un‐specked hardyhead Craterocephalus stercusmuscarum fulvus and Murray–Darling rainbowfish Melanotaenia fluviatilis. Linear growth models provided the best fit for length‐at‐age data of juvenile 0+ age large‐bodied species; whereas von Bertalanffy growth functions provided the best fit to length‐at‐age data of small‐bodied species. The results provide novel baseline data for future research in this area.

Fish and flows: Abiotic drivers influence the recruitment response of a freshwater fish community throughout a regulated lotic system of the Murray‐Darling Basin, Australia

“…Age estimates of individual fish were determined by counting daily otolith increment microstructures (Stocks, Scott & Gilligan, 2019). For large‐bodied species where few juveniles were captured during standardized sampling (eel‐tailed catfish) or where growth models poorly fitted size‐at‐age data (Murray cod and common carp), all juveniles captured were aged daily to back‐calculate their hatch date (Stocks, Scott & Gilligan, 2019).…”

“…For large‐bodied species where few juveniles were captured during standardized sampling (eel‐tailed catfish) or where growth models poorly fitted size‐at‐age data (Murray cod and common carp), all juveniles captured were aged daily to back‐calculate their hatch date (Stocks, Scott & Gilligan, 2019). For large‐bodied species, where large numbers of juveniles were caught during the standardized sampling (bony bream and golden perch), and for all small‐bodied species, fish ages were estimated from length measurements using the derived species growth model equations (Stocks, Scott & Gilligan, 2019). For small‐bodied species, estimates of fish age were not made for larger or older fish beyond the asymptote of the von Bertalanffy growth function where the relationship between size and age breaks down.…”

“…For small‐bodied species, estimates of fish age were not made for larger or older fish beyond the asymptote of the von Bertalanffy growth function where the relationship between size and age breaks down. For juvenile large‐bodied species, estimates of daily age were not extrapolated beyond the largest fish aged in the species daily age‐growth function (Stocks, Scott & Gilligan, 2019). Consequently, interpretation of back‐calculated hatch dates associated with each sampling event is constrained to the period between the species' earliest back‐calculated hatch date (determined by the species' maximum daily age or asymptote of the growth function) and latest back‐calculated hatch date (determined by the size/age at which the species was susceptible to the sampling methodology); this period is defined as the ‘focus period’.…”

“…All fish captured during standardized sampling were measured to the nearest mm. During each sampling event a sample of small‐bodied species ( n = 50 from each zone) and all juvenile large‐bodied species (<130 mm total length) were retained for daily ageing and the construction of size‐at‐age growth functions (Stocks, Scott & Gilligan, 2019).…”

“…Age estimates of individual fish were determined by counting daily otolith increment microstructures (Stocks, Scott & Gilligan, 2019). For large-bodied species where few juveniles were captured during standardized sampling (eel-tailed catfish) or where growth models poorly fitted size-at-age data (Murray cod and common carp), all juveniles captured were aged daily to back-calculate their hatch date (Stocks, Scott & Gilligan, 2019). For large-bodied species, where large numbers of juveniles were caught during the standardized sampling (bony bream and golden perch), and for all small-bodied species, fish ages were estimated from length measurements using the derived species growth model equations (Stocks, Scott & Gilligan, 2019) 2).…”