Cytological analysis of integumentary and muscular adaptations in three sand-dwelling marine teleosts, Ammodytes tobianus (Ammodytidae), Gorgasia preclara (Congridae) and Heteroconger hassi (Congridae) (Teleostei; Actinopterygii).

Jérôme Canei,Arnaud Trupia,Denis Nonclercq

doi:10.1111/jfb.14472

Abstract

Sandy bottoms are a ubiquitous environment found from sea bottoms to intertidal and freshwater zones. They are inhabited by many invertebrates and vertebrates which have developed morphological and physiological adaptations to sustain life under these particular conditions. Sandy habitats exhibit three potential constraints: abrasion, hypoxia and mechanical resistance. Here, three teleost species living in sandy environments were investigated: Ammodytes tobianus (Ammodytidae), Gorgasia preclara and Heteroconger hassi (Congridae). These teleost fishes were studied for their integument and muscular systems, which are potentially subject to sand abrasion and hypoxia, respectively. Based on histochemistry and transmission electron microscopy, we found the complex mucus system of G. preclara and H. hassi consists of two types of goblet cells and one type of sacciform cell. The secretions of both species are made of complex polysaccharides. In contrast, the scaly integument of A. tobianus has only a few goblet cells and no sacciform cells. We also highlighted, by immunohistochemistry, that the epidermal cell proliferation was much higher for this latter species, potentially resulting from the high rate of sand abrasion when A. tobianus buries itself quickly in the substrate. For all species, the major muscle fibre type was revealed by histoenzymology and corresponds to fast glycolytic fibres followed by intermediate fibres with slow fibres in the lowest proportion. Ammodytes tobianus possesses the highest fast fibre proportion (about 87% for A. tobianus and 75–78% for both garden eels). Our results provide new insights into the previously poorly studied teleost species, such as G. preclara, and allow us to highlight the complex skin histology of both garden eel species. Furthermore, the previously unknown muscle typing of these three species was determined.

Highlights

Sand is defined as a granular material, finer than gravels and coarser than silt, which is composed of particles between 0.05 and 2 mm in diameter
We note that the presence of melanocytes in the epidermis is uncommon among the teleost fishes, where this kind of cell is almost exclusively located in the dermis for a lot of species
According to the scarce literature on the subject, many hypotheses have been suggested concerning the nature of secretions and the physiological role played by sacciform cells

Summary

| INTRODUCTION

Sand is defined as a granular material, finer than gravels and coarser than silt, which is composed of particles between 0.05 and 2 mm in diameter. Some species of Pleuronectiformes use thin sand layers as camouflage Their integument has special characteristics that could retain sand particles, at the dorsal epidermal level (Spinner et al, 2016). The choice of a suitable sandy territory, regularly washed by oxygenated water, constitutes a behavioural adaptation to deal with potential hypoxia periods, like for the sandeel species Ammodytes tobianus (Robards et al, 2000). Another constraint found in these sandy habitats is reduced locomotive ability resulting from the mechanical resistance of the substrate. The first is related to the potential abrasion caused by the constant friction of sand particles; the second is related to its locomotion capacities and indirectly to the potential adaptations to low oxygen levels inside the sand

| MATERIALS AND METHODS

| RESULTS

Findings

| DISCUSSION