The Lateral Line System in Larvae of the Blind Cyprinid Cavefish, Phreatichthys andruzzii

Abstract

Scanning and transmission electron microscopic observations were made on the anterior and posterior lateral line system of larvae of the blind cavefish, Phreatichthys andruzzii. The investigations were conducted on 36 specimens belonging to three different ages of juvenile: 7, 14, and 28 days posthatching. The basic sensory unit of the mechanoreceptive system is a superficial ''neuromast,'' which is composed of sensory hair cells (HCs) embedded in nonsensory support cells (SCs) frequently covered with a cupula. Head neuromasts had the longest cupulae. These organs presented the same structure and ultrastructure in the head and along the body of all specimens of P. andruzzii of different ages. Hair cells of neuromasts of P. andruzzii larvae were pear-shaped cells 10-20 mm high and 3-5 mm in diameter. The nucleus of each hair cell was large and basally placed, the cytoplasm contained numerous mitochondria and each HC had a single long kinocilium and several short stereocilia. The majority of SCs were elongated in shape and their nuclei occupied a significant portion of the cytoplasm. The support cells at the margin of the neuromast were particularly thin. Both types of support cells possessed welldeveloped rough endoplasmic reticulum and Golgi apparatus. The size and number of neuromasts and their component cells increased with the age of larvae (ANOVA, P < 0.05). The dimensions of the neuromasts of the anterior lateral line (head) did not differ significantly from those of the posterior lateral line (trunk) (ANOVA, P > 0.05). Anat Rec, 292:423-430, 2009. 2009

Immunohistochemical and ultrastructural properties of the larval ciliary band-associated strand in the sea urchin Hemicentrotus pulcherrimus

“…The presence of Syn in the CBAS is another observation supporting the sensory function. Neural signal transmission-associated Syn is expressed in sensory cells, such as the auditory organ of chicks [ 52 ] and humans [ 53 ], taste bud cells in rats [ 54 ], rhodopsin-positive cells of rats [ 55 ], the human retina [ 56 ], and the lateral line of the blind cavefish larva [ 57 ] and zebrafish [ 58 ].…”

Cavefish eye loss in response to an early block in retinal differentiation progression

“…The adult fish completely lack pigment and eyes, as well as scales. Conversely the number of neuromast sensory cells is dramatically increased (Berti et al, 2001; Dezfuli et al, 2009a; Dezfuli et al, 2009b). The eyes in Phreatichthys have been shown to initially develop, but then degenerate and are eventually overgrown by orbit tissue and skin (Berti et al, 2001).…”

Extra-Visual Systems in the Spatial Reorientation of Cavefish

“…In conclusion, our findings seem to contribute to a greater understanding of spatial cognitive skills in re-orientation tasks, adding evidence of this ability even in blind cavefish species, necessarily resorting to the use of non-visual sensory modalities, such as, for example, the very large number of lateral line neuromasts 47 , 48 . The ability of guidance through the use of spatial environmental information (geometry and landmarks) is crucial to the survival of animals.…”

“…Many experimental evidences showed that fish use the lateral line to perceive hydrodynamic information (water displacements and pressure fluctuation caused by swimming) for different behavioural tasks as prey detection, predator avoidance, intraspecific communication, schooling and objects discrimination 43 . In parallel to the degeneration of the eyes during early development 44 , 45 , cavefish have a hypertrophy of the lateral line system (increasing number and dimension of neuromasts) and the sense of smell (surface area of the olfactory epithelium and dimension of olfactory bulbs) 46 – 48 . The use of blind species as models could be very interesting because they allow us to observe and understand how and in what degree the lateral line provides information to the animal on the surrounding environment and if its function (in terms of available information) could be comparable to that of the sight.…”