Baby fish shaped by mothers' stress

Pomacentrus amboinensis Maternal

Stressed reef fish mothers produce highly active babies, and this affects survival and has important implications for fish populations in a changing environment, according to new research.

Dr Monica Gagliano, a research fellow with the AIMS@JCU joint venture, worked with colleague Dr Mark McCormick from the ARC Centre of Excellence for Coral Reef Studies (James Cook University) on a study that deepens our understanding of how stress affects the dynamics of wild fish populations and hence how fish may cope with increasing human-induced stresses.

This work, published in the journal Oecologia*, has implications for management of fisheries resources as well as increasing our knowledge of the basic physiological processes governing the life cycles of fish.

Dr Gagliano and Dr McCormick have shown that the parental environment of a common reef species, Ambon damsel fish, is crucial for the future lives of their offspring. In their laboratory research, they determined the effects of maternal stress on offspring characteristics by exposing fertilised fish eggs gathered from the wild to different levels of the stress hormone cortisol.

'These baby fish can’t make these important hormones until later in life, so their whole initial development is determined by hormones they obtain from their mothers,' Dr McCormick said.

Previous studies had shown that females of this species release cortisol from their ovaries in response to environmental stress; those fish in isolated reefs with few predators or competitors show low levels of the hormone while those in high stress environments bathe their eggs in high levels of the hormone. The present study shows just what all that stress hormone can do to the eggs.

'If the mother fish is more stressed and she passes on more cortisol, then the offspring will have a faster developmental rhythm and therefore errors will be more likely in their development. One likely result of this is that the offspring are born asymmetrical,' Dr Gagliano said.

Research published in 2008 by Dr Gagliano and colleagues showed that fish born with asymmetrical ear bones (otoliths) face huge problems negotiating the open ocean stage of their development, and many are lost of sea before they can settle on a reef to breed. Their asymmetry interfered with their hearing, making it hard from them to home in on reef-related sounds.

Recent work by Ms Tove Lemberget at JCU, with Dr McCormick, also published in Oecologia, found that asymmetry of the larval stages was strongly related to survival in Caribbean lizardfishes (see Lemberget and McCormick 2009, 'Replenishment success linked to fluctuating asymmetry in larval fish').

Dr Gagliano’s latest research also shows that stress, in this case maternal stress, has a large measurable effect on the shape of the ear bones, with those baby fish receiving the high dose of cortisol being more than twice as likely to have asymmetrical ear bones compared with those that received none.

Together, this research suggests that stressed mothers produce offspring that are much less likely to survive. Mothers in healthy, low stress environments are likely to contribute most to the next generation.

*The Oecologia paper is titled 'Hormonally-mediated maternal effects shape offspring survival potential in stressful environments'.

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