The post-cranial body armor of the armored Agonidae fishes - How far do the morphological scale modifications go?

The family of the Agonidae is characterized by the presence of modified bony scales that form a protecting armor against predators. Despite some very intensive research concerning the skeletal cranial and postcranial anatomy of different Agonids, little information is available in the literature concerning the morphology of these bony scales. In this paper, three common species of the Northeastern Pacific Ocean are microscopically (both stereo and scanning electron microscopy) investigated to show that these bony plates are (a) morphologically different from regular fish scales, (ii) build for strength but also for minimizing the weight of the armor plates and (iii) morphologically different between different species

The post-cranial body armor of the armored Agonidae fishes - How far do the morphological scale modifications go?

The family of the Agonidae is characterized by the presence of modified bony scales that form a protecting armor against predators. Despite some very intensive research concerning the skeletal cranial and postcranial anatomy of different Agonids, little information is available in the literature concerning the morphology of these bony scales. In this paper, three common species of the Northeastern Pacific Ocean are microscopically (both stereo and scanning electron microscopy) investigated to show that these bony plates are (a) morphologically different from regular fish scales, (ii) build for strength but also for minimizing the weight of the armor plates and (iii) morphologically different between different species

Musculoskeletal anatomy and feeding performance of pre-feeding engyodontic larvae of the European eel (Anguilla anguilla)

Being part of the elopomorph group of fishes, Anguillidae species show a leptocephalus larval stage. However, due to largely unknown spawning locations and habitats of their earliest life stages, as well as their transparency, these Anguilla larvae are rarely encountered in nature. Therefore, information regarding the early life history of these larvae, including their exogenous feeding strategy and feeding performance, is rather scarce. To better understand the structural basis and functional performance of larval feeding in captivity, the functional morphology of the cranial musculoskeletal system in pre- and first-feeding engyodontic leptocephali of the European eel (Anguilla anguilla) was studied. A 3D reconstruction of the feeding apparatus (head of the leptocephali < 1 mm) was used to visualize and describe the musculoskeletal changes throughout these stages. To analyze the ontogenetic changes in the functionality of the feeding apparatus towards the active feeding phase, 3D data of joints, levers and muscles derived from the reconstructions were used to estimate bite and joint reaction forces (JRFs). Observing a maximum estimated bite force of about 65 lN (and corresponding JRFs of 260 lN), it can be hypothesized that leptocephalus larvae are functionally constrained to feed only on soft food particles. Additionally, potential prey items are size delimited, based on the theoretically estimated average gape of these larvae of about 100 lm. This hypothesis appears to be in line with recent observations of a diet consisting of small and/or gelatinous prey items (Hydrozoa, Thaliacea, Ctenophora, Polycystenia) found in the guts of euryodontic leptocephalus larvae

Gelatinous plankton is important in the diet of European eel (Anguilla anguilla) larvae in the Sargasso Sea

Limited insight into eel larvae feeding and diet prevents a holistic overview of the life-cycle of catadromous eels and an understanding of the ecological position of their early stages in marine waters. The present study evaluated the diet of larval European eel, Anguilla anguilla - a critically endangered species. Next-generation 18S rRNA gene sequencing data of Sargasso Sea eel larvae gut contents and marine snow aggregates was compared with a reference plankton database to assess the trophic relations of eel larvae. Gut contents of A. anguilla larvae were not well explained by the eukaryotic composition of marine snow aggregates; gut contents being dominated by gene sequences of Hydrozoa taxa (phylum Cnidaria), while snow aggregates were dominated by Crustacea taxa. Pronounced differences between gut contents and marine snow aggregates were also seen in the prokaryotic 16S rRNA gene composition. The findings, in concert with significant abundances of Hydrozoa in the study area, suggest that Hydrozoa plankton are important in the diet of A. anguilla larvae, and that consideration of these organisms would further our understanding of A. anguilla feeding strategies in the oligotrophic Sargasso Sea, which may be important for potential future rearing of A. anguilla larvae in captivity