Though common in mammals and birds, just a few teleost fish developed the ability to produce and retain heat in their bodies. This evolutionary trait, known as endothermy, appeared several times independently within the lineage of the abundant and diverse spiny-rayed teleosts. Amongst those, tunas and opahs (large oceanic fish with striking red fins) developed the ability to generate heat via their swimming muscles and retain it with specialised blood vessels. Of these, only tunas were known to have bones containing embedded cells called osteocytes.
A paper by Postdoctoral Researcher Dr Donald Davesne, and colleagues from the University of Oxford Department of Earth Sciences, the Muséum national d’Histoire naturelle (Paris), University of Michigan and the University of Poitiers reveals that opahs have a similar cellular bone structure to tunas, hinting at a common physiological mechanism linking the cellular structure of fish bones to their capacity to generate heat.
“No one had ever looked at the bone structure of the opahs before,” explains Davesne. “When we started to look at the bones of modern opahs, we saw the distinct signs of osteocytes, which suggested independent evolution of cellular bone. The link between cellular bone and endothermy in tunas had been suggested in the past, and our research reveals further evidence that this could be a possibility, now that we see it in another lineage.”
Davesne’s research is to further understand osteocytes in various modern and fossil fishes, by reconstructing them in 3D to understand their relationship to various parameters including genome size.
The paer, ‘Histology of the endothermic opah (Lampris sp.) suggests a new structure-function relationship in teleost fish bone’, by Donald Davesne, François J. Meunier, Matt Friedman, Roger B. J. Benson and Olga Otero was published in the Royal Society’s Biology Letters doi.org/10.1098/rsbl.2018.0270
In a recent, unrelated paper, Davesne offers a glimpse into the ecology of a fish from the Cretaceous period. Completing work undertaken whilst a PhD student at the MNHN in Paris, Davesne studied a fossil spiny-rayed fish found in the Kem Kem beds in Morocco, which had been found with an almost intact intestine.
“This sample was very unusual, as it is rare to find soft tissue preserved so faithfully. We could see where the intestine lay within the body of the fish, complete with curves and folds. My colleague Pierre Gueriau (now at the University of Lausanne) analysed the intestine under synchrotron X-rays, and was able to reveal traces elements that confirmed our theory that this freshwater fish fed on a diet that included plant life, and which explains the longer intestine than is typically found in similar carnivorous marine fish, further developing our understanding of freshwater environments in the Cretaceous.”
Davesne worked on the sample with colleagues in CNRS, SOLEIL Synchrotron and the MNHN in France.
Paper: ‘Exceptional preservation of a Cretaceous intestine provides a glimpse of the early ecological diversity of spiny-rayed fishes (Acanthomorpha, Teleostei)’ by Donald Davesne, Pierre Gueriau, Didier B. Dutheil et Loïc Bertrand was published in Scientific Reports DOI :10.1038/s41598-018-26744-3
Photo: Opah caught and released on a longline set off of the Channel Islands off of California. Image credit: Southwest Fisheries Science Center, NOAA Fisheries Service