Brain and sense organ anatomy and histology of two species of phyletically basal non‐Antarctic thornfishes of the Antarctic suborder Notothenioidei (Perciformes: Bovichtidae)

Abstract

The predominantly non-Antarctic family Bovichtidae is phyletically basal within the perciform suborder Notothenioidei, the dominant component of the Antarctic fish fauna. In this article we focus on the South Atlantic bovichtids Bovichtus diacanthus, the klipfish from tide pools at Tristan da Cunha, and Cottoperca gobio, the frogmouth from the Patagonian shelf and Falkland Islands. We document the anatomy and histology of the brains, olfactory apparatus, retina, and cephalic lateral line system. We also use the microvascular casting agent Microfil to examine ocular vascular structures. We provide detailed drawings of the brains and cranial nerves of both species. Typical of perciforms, the brains of both species have a well-developed tectum and telencephalon and robust thalamic nuclei. The telencephalon of C. gobio is prominently lobed, with the dorsomedial nucleus more conspicuous than in any other notothenioid. The corpus cerebelli is relatively small and upright and, unlike other notothenioids, has prominent transverse sulci on the dorsal and caudal surfaces. Areas for lateral line mechanoreception (eminentia granularis and crista cerebellaris) are also conspicuous but olfactory, gustatory, and somatosensory areas are less prominent. The anterior lateral line nerve complex is larger than the posterior lateral line nerve in B. diacanthus, and in their cephalic lateral line systems both species possess branched membranous tubules (which do not contain neuromasts) with small pores. These are especially complex in B. diacanthus where they become increasingly branched and more highly pored in progressively larger specimens. Superficial neuromasts are sparse. Both species have duplex (cone and rod) retinae that are 1.25-fold thicker and have nearly 5-fold more photoreceptors and than those of most Antarctic notothenioids. Convergence ratios are also high for bovichtids. Bovichtus diacanthus has a yellow intraocular filter in the dorsal aspect of the cornea. Both species are unique among notothenioids in possessing all three vascular structures present in the generalized teleostean eye: the choroid rete mirabile, the lentiform body (also a rete), and the falciform process. When comparing the phyletically derived Antarctic clade exemplified by the families Artedidraconidae, Bathydraconidae, and Channichthyidae to the phyletically basal bovichtids, we observe phyletic regression and reduction in some regions of the brain and in some sensory modalities that are well displayed in bovichtids. In the phyletically derived families the brain is less cellular and nuclei are smaller and less prominent. In some species reduction in the size of the telencephalon, tectum, and corpus cerebelli imparts a "stalked" appearance to the brain with the neural axis visible between the reduced lobes. There is also a phyletic reduction in the number of ocular vascular structures from three in bovichtids to one or none in artedidraconids, bathydraconids, and channichthyids. There are no morphological features of bovichtid brains and sense or...

Brain and sense organ anatomy and histology of the Falkland Islands mullet, Eleginops maclovinus (Eleginopidae), the sister group of the Antarctic notothenioid fishes (Perciformes: Notothenioidei)

“…These have been termed ''canaliculi'' in notothenioid systematic work (Jakubowski, 1971;Andersen, 1984;DeWitt et al, 1990). They are straight and unbranched in Eleginops of the size range that we examined, although it is possible they become more complexly branched during ontogeny as has been documented in a number of groups including clupeids and bovichtids (Stephens, 1985;Eastman and Lannoo, 2007). Along the infraorbital canal, some of membranous canals arise between and perpendicular to the bony segments while others are continuous with the bony canals (Fig.…”

“…6B). As in all other notothenioids except the bovichtid Cottoperca gobio (Eastman and Lannoo, 2007), Eleginops maclovinus has an oval rosette with olfactory lamellae arranged perpendicular to a central raphe (Fig. 6B), the Type G arrangement in the classification of Yamamoto (1982).…”

“…While both bovichtids (Eastman and Lannoo, 2007) and Eleginops have a relatively small saccus, the saccus is well-developed in the Antarctic clade , 2003a,b, 2004Lannoo and Eastman, 2000) and is best defined as Type 3 in the classification of Tsuneki (1992).…”

The brain of Brycon orbignyanus (Valenciennes, 1850) (Teleostei: Characiformes: Bryconidae): gross morphology and phylogenetic considerations

“…When the described procedure is complete, the brain should be completely free from the neurocranium. Meek & Nieuwenhuys (1998) and Striedter (2005), with a single modification: fish brains descriptions usually follow the posteroanterior direction (e.g., Meek & Nieuwenhuys, 1998), but herein we chose to follow Striedter (2005) in adopting the anteroposterior direction, the most commonly used for vertebrates as a whole (see Bauchot et al, 1989;Striedter, 2005;Eastman & Lannoo, 2007, 2008 for fishes; ten Donkelaar, 1998a for amphibians; ten Donkelaar, 1998b for reptiles and Walsh & Milner, 2011 for avians). For illustration and description purposes, the brains were divided into telencephalon, mesencephalon, diencephalon, rhombencephalon and medulla spinalis (Fig.…”

Divergence of brain and retinal anatomy and histology in pelagic antarctic notothenioid fishes of the sister taxa Dissostichus and Pleuragramma

“…As a means of apportioning the influence of phylogentic and ecological factors shaping brain morphology, Kotrschal et al (1998) call for investigations of closely related perciform species that differ in body size, habitat utilization and behavior. Having established the large‐scale pattern of neural and sensory morphology for families and genera of Antarctic perciform notothenioids (Eastman and Lannoo,1995,2003a,b,2004,2007,2008; Lannoo and Eastman,2000), we are in a position to address this topic. Using the ecologically vital but neuroanatomically unstudied genera Dissostichus and Pleuragramma , we will provide such a comparison and analysis of the brains and retinae of sympatric sister species of notothenioids that, while sharing the pelagic lifestyle, have diverged in body size, diet, habitat depth, activity levels and tendency to migrate.…”