Prolonged exposure to low oxygen improves hypoxia tolerance in a freshwater fish

Persistent hypoxic or low-oxygen conditions in aquatic systems are becoming more frequent worldwide, causing large-scale mortalities to aquatic fauna. It is poorly understood, however, whether species can acclimate to long-term hypoxic conditions. In two experiments, we exposed juvenile freshwater fish (Murray cod, Maccullochella peelii) to low-oxygen conditions and investigated acclimation effects. Experiment 1 determined how responses could be modified by exposure to different temperatures (20, 24 and 28°C) and oxygen conditions (control 6-8 mgO₂ L⁻¹ and low-oxygen 3-4 mgO₂ L⁻¹) over 30 days. Experiment 2 determined the acclimation ability of fish exposed to two temperatures (20 and 28°C) and low-oxygen conditions (3-4 mgO₂ L⁻¹) for three different acclimation periods (7, 14 and 30 days). Responses were measured by determining critical oxygen tension (Pcrit), loss of equilibrium and aerobic capacity using resting respirometry. In experiment 1, resting oxygen requirements were negatively affected by long-term low-oxygen exposure except at the highest temperature (28°C). However, long-term acclimation in low-oxygen improved tolerance as measured by loss of equilibrium but not Pcrit. In experiment 2, fish could tolerate lower oxygen levels before reaching loss of equilibrium after 7 days acclimation, but this declined overtime. Murray cod were most tolerant to low-oxygen at the lowest temperature (20°C) and shortest exposure time (7 days). Extended low-oxygen exposure resulted in reduced aerobic capacity of fish particularly at the lowest temperature. While prior exposure to low-oxygen may allow fish to cope with hypoxic conditions better in the long-term, acclimation time was inversely related to tolerance, suggesting that resistance to hypoxia might decrease as a function of exposure time. Our study fills a much-needed gap in our understanding of how freshwater species acclimate to hypoxia, and in particular, how exposure to prolonged periods of low-oxygen and elevated temperatures affect organisms physiologically.Kayla L. Gilmore, Zoe A.Doubleday and Bronwyn M. Gillander

Techniques for Estimating the Age and Growth of Molluscs: Cephalopoda

Global abundances and commercial fisheries of cephalopods have increased over recent decades, creating a need for effective fishery management. This management is often focused on the ability to ascertain the age structure of key populations. There are several main techniques for age and growth rate determination in cephalopods. Because of biological differences between species groups, not all techniques are applicable for every species. This review outlines the use of five main ageregistering structures (statoliths, gladii, beaks, stylets, and eye lenses) along with one chemical aging technique (lipofuscin) and their application to cephalopod species groups.En prensa1,04

Pet or pest? Stable isotope methods for determining the provenance of an invasive alien species

The illegal pet trade facilitates the global dispersal of invasive alien species (IAS), providing opportunities for new pests to establish in novel recipient environments. Despite the increasing threat of IAS to the environment and economy, biosecurity efforts often lack suitable, scientifically-based methods to make effective management decisions, such as identifying an established IAS population from a single incursion event. We present a proof-of-concept for a new application of a stable isotope technique to identify wild and captive histories of an invasive pet species. Twelve red-eared slider turtles (Trachemys scripta elegans) from historic Australian incursions with putative wild, captive and unknown origins were analysed to: (1) present best-practice methods for stable isotope sampling of T. s. elegans incursions; (2) effectively discriminate between wild and captive groups using stable isotope ratios; and (3) present a framework to expand the methodology for use on other IAS species. A sampling method was developed to obtain carbon (δ13C) and nitrogen (δ15N) stable isotope ratios from the keratin layer of the carapace (shells), which are predominantly influenced by dietary material and trophic level respectively. Both δ13C and δ15N exhibited the potential to distinguish between the wild and captive origins of the samples. Power simulations demonstrated that isotope ratios were consistent across the carapace and a minimum of eight individuals were required to effectively discriminate wild and captive groups, reducing overall sampling costs. Statistical classification effectively separated captive and wild groups by δ15N (captive: δ15N‰ ≥ 9.7‰, minimum of 96% accuracy). This study outlines a practical and accessible method for detecting IAS incursions, to potentially provide biosecurity staff and decision-makers with the tools to quickly identify and manage future IAS incursions.Katherine G.W. Hill, Kristine E. Nielson, Jonathan J. Tyler, Francesca A. McInerney, Zoe A. Doubleday, Greta J. Frankham, Rebecca N. Johnson, Bronwyn M. Gillanders, Steven Delean, Phillip Casse

Statolith chemistry: a new tool to understand the ecology and provenance of octopus

Growing commercial interest in octopus fisheries has increased the need to develop rapid and inexpensive methods to determine the geographical origins (provenance) of individuals. Identifying the provenance of marine species not only supports high-quality and sustainable fisheries, as seafood distributors are held accountable for accurately sourced products, but can address important ecological questions on movement and connectivity. Multi-elemental signatures in statoliths, the cephalopod equivalent of otoliths, could act as geographical proxies but have never been analysed in octopus. As such, we investigated the statolith chemistry of commercially harvested Octopus berrima collected across two seasons (summer and winter) and from four sites along the South Australian coast with different temperature and salinity profiles. Statoliths were analysed using laser ablation inductively coupled plasma mass spectrometry, targeting the central portion of the structure, to measure concentrations of chosen elements (⁷Li, ²⁴Mg, ⁵⁵Mn, ⁸⁸Sr, ¹³⁷Ba, ¹¹B, ²³Na, ³¹P, ³⁹K, ⁵⁹Co, ⁶⁰Ni, ⁶⁵Cu, ⁶⁶Zn, ²⁰⁸Pb). Significant differences between region and season were found for most elements, except ⁸⁸Sr and ⁶⁰Ni. Cross-validation classification found that 85% of octopus from environmentally distinctive regions were able to be correctly classified back to region of origin, regardless of harvest season. Regions with similar environmental profiles had lower classification success (70%). We also found that ¹¹B, ¹³⁷Ba, and ⁵⁵Mn contributed most to the discrimination among regions. This study reveals that distinctive geographic signatures are present in statoliths of octopus, establishing the potential of statolith elemental chemistry as a powerful tool for tracking the movement and provenance of octopus.Divya S. Daryanani, Jasmin C. Martino, Zoë A. Doubleda

Elevated carbon dioxide and temperature affects otolith development, but not chemistry, in a diadromous fish

Abstract not availableJasmin Martino, Zoë A. Doubleday, Skye H. Woodcock, Bronwyn M. Gillander

Experimental support towards a metabolic proxy in fish using otolith carbon isotopes

Metabolic rate underpins our understanding of how species survive, reproduce and interact with their environment, but can be difficult to measure in wild fish. Stable carbon isotopes (δ13C) in ear stones (otoliths) of fish may reflect lifetime metabolic signatures but experimental validation is required to advance our understanding of the relationship. To this end, we reared juvenile Australasian snapper (Chrysophrys auratus), an iconic fishery species, at different temperatures and used intermittent-flow respirometry to calculate standard metabolic rate (SMR), maximum metabolic rate (MMR) and absolute aerobic scope (AAS). Subsequently, we analysed δ13C and oxygen isotopes (δ18O) in otoliths using isotope-ratio mass spectrometry. We found that under increasing temperatures, δ13C and δ18O significantly decreased, while SMR and MMR significantly increased. Negative logarithmic relationships were found between δ13C in otoliths and both SMR and MMR, while exponential decay curves were observed between proportions of metabolically sourced carbon in otoliths (Moto) and both measured and theoretical SMR. We show that basal energy for subsistence living and activity metabolism, both core components of field metabolic rates, contribute towards incorporation of δ13C into otoliths and support the use of δ13C as a metabolic proxy in field settings. The functional shapes of the logarithmic and exponential decay curves indicated that physiological thresholds regulate relationships between δ13C and metabolic rates due to upper thresholds of Moto. Here, we present quantitative experimental evidence to support the development of an otolith-based metabolic proxy, which could be a powerful tool in reconstructing lifetime biological trends in wild fish.Jasmin C. Martino, Zoë A. Doubleday, Ming-Tsung Chung and Bronwyn M. Gillander

First feeding and food imprinting in octopus

Published Online: 27 June 2023Food imprinting has both ecological and evolutionary significance but the generality of these patterns for octopods remains unknown. We aim to determine the prey preference of Octopus berrima hatchlings and whether it may be modified through imprinting. Firstly, hatchlings were given isopods, amphipods and mussels to determine their prey preference ranking. In a separate experiment, embryos were exposed to the visual and chemical stimuli of either isopods, amphipods or mussels separately at least a week before hatching. A prey preference test on hatchlings using all three prey types was conducted. We found that O. berrima had a preference ranking of isopods > amphipods > mussels. However, they retained their isopod prey preference regardless of the prey type they were embryonically exposed to, indicating that it is likely pre-determined as a result of innate biological processes rather than from life experience, providing evidence that imprinting does not occur in O. berrima.Qiaz Q.H. Hua, Manuel Nande, Zoe A. Doubleday, Bronwyn M. Gillander