# The anatomy of the endocrine pancreas among teleosts: phylogenetic implications

Bruno Chanet, Wei-Jen Chen, Nalani Schnell, Claude Guintard

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Bruno Chanet, Wei-Jen Chen, Nalani Schnell, Claude Guintard. The anatomy of the endocrine pancreas among teleosts: phylogenetic implications. 2017 meeting of the Asian Society of Ichthyologists, Aug 2017, Ho-Chi-Minh-City, Vietnam. 2017. [hal-03972974](https://hal.science/hal-03972974)

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# The anatomy of the endocrine pancreas among teleosts: phylogenetic implications

Bruno Chanet ¹, Wei-Jen Chen ², Nalani Schnell ¹ & Claude Guintard ³

¹ ISYEB, UMR7205 MNHN-CNRS-UPMC-EPHE, Muséum national d'Histoire naturelle, Dpt Systématique et Evolution, CP30, 25 rue Cuvier, 75005 Paris, France
² Institute of Oceanography, National Taiwan University, no. 1 sec. 4, Roosevelt Road, Taipei 10617, Taiwan
³ Laboratoire d'Anatomie Comparée, ONIRIS - Ecole Nationale Vétérinaire de l'Agroalimentaire et de l'Alimentation, Nantes Atlantique, Route de Gachet, CS 40 706, 44307 Nantes Cedex 03, France.

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Oniris

École Nationale
Vétérinaire, Agroalimentaire et de l'Alimentation

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## Introduction

In vertebrates, the regulation of glycemia (glucose level in the blood) is mainly controlled by hormones from the endocrine part of the pancreas: insulin and glucagon. Anatomically, the endocrine cells of the pancreas form minute islets, called the islets of Langerhans, that are scattered in the other pancreas tissues. Generally, these tissues diffuse between the mesenteries and the coils of the intestine. However, according to the literature, some teleostean species display a more or less compact endocrine pancreas, with a giant or principal islet, named Brockmann Body (BB) (Figs 1 to 4).

The objective of this study is to examine the anatomical diversity of this organ in the *Actinopterygii* in a phylogenetic context.

<figure><img src="image_5.png" /><figcaption>**Fig. 1** The BB in *Pholis gunnelus* (Pholidae), modified from Rennie (1903).</figcaption></figure>

<figure><img src="image_6.png" /><figcaption>**Fig. 2** Mechanical parasagittal section of *Perca fluviatilis* (Percidae), modified from Guintard *et al.* (2017).</figcaption></figure>

<figure><img src="image_7.png" /><figcaption>**Fig. 3** The BB in *Gymnoscopelus braueri* (Myctophidae).</figcaption></figure>

## Materials & Methods

A survey of the comparative anatomy of the endocrine pancreas on the basis of literature, dissections and MRI for the specimens across 300 actinopterygian species in 46 orders and 119 families was carried out. The recent hypothesis of actinopterygian phylogeny based on molecular data was used to illustrate this morphological evolution (Fig. 5).

## Results & Discussion

The result revealed a wide range of variation. We observed that: (1) this variation was categorized first by the organization of the organ: diffused versus compact, with few BB (Figs 1 to 4); (2) the large endocrine pancreatic nodules have appeared several times during the evolution of the Teleostei: at least in some Ostariophysi, some Salmoniformes, Ateleopodiformes and the immense majority of the lineages within the Ctenosquamata (Myctophiformes plus Acanthomorpha) (Fig. 5).

<figure><img src="image_8.png" /><figcaption>**Fig. 4** The BB in *Ateleopus purpurus* (Ateleopodidae).</figcaption></figure>

<figure><img src="image_9.png" /><figcaption>**Fig. 5** The anatomy of endocrine pancreas among actinopterygian fishes</figcaption></figure>

According to the most recent molecular hypotheses (Chen *et al.* 2014; Betancur-R *et al.* 2013), Ateleopodiformes form a polytomy with Aulopiformes and Ctenosquamata. The presence of a BB in Ateleopodiformes and Ctenosquamata may be considered as a derived character shared by them, supporting thus their close relationship. Within the Acanthomorpha, the absence of BB is observed in parrotfishes and some of their labrid allies. More investigations are still needed to corroborate the existence or absence of BB as putative synapomorphies for these lineages.

## References

* Betancur-R., R. *et al.* (2013). The Tree of Life and a new classification of bony fishes. *PLoS Currents Tree of Life*. 2013 Apr 18

* Chen, W.-J. *et al.* (2014) New insights on early evolution of spiny-rayed fishes (Teleostei: Acanthomorpha). *Frontiers in Marine Science* 1, 53

* Guintard, C. *et al.* (2017). Exploration de l'anatomie de la perche commune *Perca fluviatilis* (L. 1758) [Serraniformes, Percidae]. *Cahiers d'Anatomie Comparée*, 2017, 9:1-20.

* Rennie, J. (1903). On the occurrence of a 'principal islet' in the pancreas of Teleostei. (Preliminary note.). *Journ. Anat. and Phys.*, 37:375-378.

2017 meeting of the Asian Society of Ichthyologists at University of Science-VNU HCM, Ho Chi Minh City, Vietnam on 22-24 Aug. 2017