Daniela Minelli

The development of NADPH-diaphorase and nitric oxide synthase in the visual system of the cichlid fish, Tilapia mariae

The pattern of NADPH-diaphorase expression was studied in the retina and optic tectum of the cichlid fish Tilapia mariae during the first developmental stages. NADPH-diaphorase activity was seen early, at hatching. In the retina a few cell bodies of the retinal inner nuclear layer showed a faint labeling. Scattered labeled cells were found in the stratum periventriculare of the optic tectum, while the optic nerve was unlabeled. Two days after hatching, the number of labeled neurons increased in the inner nuclear layer and a few stained cell bodies were also scattered in the ganglion cell layer. Both the inner and outer plexiform layers showed a diffuse staining and the optic nerve was devoid of labeling. In the optic tectum several positive cells in the periventricular layer, with their dendritic trees extending in the superficial fibrous layer, were found. In 1-month-old Tilapia, NADPH-diaphorase staining and nitric oxide synthase immunoreactivity were found to overlap in both the retina and optic tectum. The density of NADPH-diaphorase labeled neurons in the inner nuclear layer of the retina and in the stratum periventriculare of the optic tectum was largely reduced in comparison with 2 days posthatching embryos. These findings indicated an early and transient production of nitric oxide in the retina and optic tectum of Tilapia, suggesting a functional role for nitric oxide in the development of visual structures in aquatic vertebrates.

An exceptionally preserved Eocene shark and the rise of modern predator–prey interactions in the coral reef food web

BackgroundFollowing extreme climatic warming events, Eocene Lagerstätten document aquatic and terrestrial vertebrate faunas surprisingly similar to modern counterparts. This transition in marine systems is best documented in the earliest teleost-dominated coral reef assemblage of Pesciara di Bolca, northern Italy, from near the end of the Eocene Climatic Optimum. Its rich fauna shows similarities with that of the modern Great Barrier Reef in niche exploitation by and morphological disparity among teleost primary consumers. However, such paleoecological understanding has not transcended trophic levels above primary consumers, particularly in carcharhiniform sharks.ResultsWe report an exceptionally preserved fossil school shark (Galeorhinus cuvieri) from Pesciara di Bolca. In addition to the spectacular preservation of soft tissues, including brain, muscles, and claspers, this male juvenile shark has stomach contents clearly identifiable as a sphyraenid acanthomorph (barracuda). This association provides evidence that a predator–prey relationship between Galeorhinus and Sphyraena in the modern coral reefs has roots in the Eocene. A growth curve of the living species of Galeorhinus fitted to G. cuvieri suggests that all specimens of G. cuvieri from the lagoonal deposits of Bolca represent sexually and somatically immature juveniles.ConclusionThe modern trophic association between higher-degree consumers (Galeorhinus and Sphyraena) has a counterpart in the Eocene Bolca, just as Bolca and the Great Barrier Reef show parallels among teleost primary consumers. Given the age of Bolca, trophic networks among consumers observed in modern coral reefs arose by the exit from the Climatic Optimum. The biased representation of juveniles suggests that the Bolca Lagerstätte served as a nursery habitat for G. cuvieri. Ultraviolet photography may be useful in probing for exceptional soft tissue preservation before common acid preparation methods.

Telencephalo-habenulo-interpeduncular connections in the brain of the shark Chiloscyllium arabicum.

The telencephalo-habenulo-interpeduncular connections have been studied in the brain of the cartilaginous fish Chiloscyllium arabicum. In addition to telencephalic and diencephalic projections to the habenula and to habenulo-interpeduncular projection, the presence of a direct telencephalo-interpeduncular connection confirmed some homologies of this system in cartilaginous fishes with actinopterigian fishes and land vertebrates.

Reproductive biology and substitution of two species of Nassariidae

Reproductive biology of Nassarius reticulatus is well known, but informations about Nassarius mutabilis are scarce; we have so undertaken a macroscopical and histological study to clear the reproductive biology of this species.

Comparative aspects of habenulae in some species of Chondrohycthes and Ostehycthes

Diencephalic habenular nuclei of several species of Chondrohycthes and Ostehycthes fishes were investigated in order to ascertain their asymmetry. Raja asterias, Squalus acanthias, Mustels mustelus, Scyliorhinus canicula and Scyllium stellare show the left habenula larger than the right, as occurs in the elasmobranchs till now investigated. Among the six species of teleostean fishes we studied, the habenulae of Liza aurata, Anguilla anguilla and Trisopterus minutus are symmetrical, while in Lepidorhombus boscii, Platichthys flesus and Solea vulgaris the habenulae are slightly asymmetrical. This finding might suggest a relation, to be better investigated, among bentic life and habenular asymmetry in teleostean.