The secret lives of fish

Fish have secret lives in complex three-dimensional environments. Yet biologists need a careful understanding of population characteristics and dynamics to sustainably manage wild fish.

As direct monitoring can be costly and logistically difficult, scientists are attempting to create chemical proxies to retrospectively track hidden histories.

Chemical signatures in fish tissues can contain a wealth of information about past biological and environmental conditions.

In particular, stable isotope proxies can be a powerful tool for reconstructing physiological and ecological change. Stable carbon isotopes in hard and soft-tissues may be able to reconstruct diet and metabolic histories through direct links between consumer tissues and diet.

However, the incorporation of carbon isotopes can be affected by both intrinsic factors (such as physiology) and extrinsic factors (such as water conditions). Our recent paper investigated these effects by conducting a controlled laboratory experiment on juvenile fish.

Our study species was Australasian snapper (Chrysophrys auratus), a commercially, recreationally and culturally iconic fishery species. We reared snapper in increasing temperature conditions for 2-months and then analysed the carbon isotope signatures in ear bones (otoliths), muscle and liver.

We found significant temperature and metabolic effects on carbon isotope incorporation into all tissues. We found metabolic rate altered the partitioning from carbon sources into otoliths, which acted as an indirect proxy of metabolic rate.Additionally, while carbon isotopes in muscle and liver reflected diet signatures, significant differences in the signatures between the tissues and temperature treatments suggested metabolic influences.

This study deepened our understanding of internal and external drivers on chemical proxies in fish tissues.

Improved insight into these proxies enhance their use in the field to unearth the hidden biological and ecological histories of fish.