Studies on the photoreceptors ofAnchoa mitchilliandA. hepsetus(Engraulidae) with particular reference to the cones

Abstract

Photoreceptors of anchovies Anchoa mitchilli and A. hepsetus consist of normal rods and two unusual kinds of cones. The latter lie in single vertical rows, and the rods lie between them. Both participate in photomechanical movements, and movement of the cones is closely coordinated with that of pigment cell processes. There are long cones having a cuneate outer segment and short cones having a bilobed outer segment. Long and short (bifid) cones alternate within a row and are staggered between adjacent rows. Both kinds possess calycal processes; long cones have a lateral sac or accessory outer segment. The long and short cones are associated to form a structure called a cone unit, which consists of the outer segment and ellipsoid of a long cone joined to two outer segment lobes of two adjacent short cones. The lobes of the latter are partly enclosed by the ellipsoid of the long cone. A cone row consists of a row of cone units isolated from each other by processes of the pigment epithelium containing stacks of guanine crystals which form a tapetum. Dorsal and ventral faces of inner segments have contact zones characterized by subsurface cisternae. Lamellae in the cone outer segments are arranged longitudinally with respect to the cell axis and short and long cone lamellae are perpendicular to each other; lamellae of the rods are transverse. Long cone lamellae are perpendicular to the cone row, and in the central retina are almost horizontal to the long axis of the body. Some vesicular/tubular structures also occur in the cone outer segments. Outer and inner segments of cones are joined by a broad connecting structure containing a stalk and root portion corresponding to a modified and reduced cilium shaft and centriole, respectively. The rod has a typical connecting stalk. Mitochondria of cone ellipsoids have expanded perimitochondrial spaces between outer and inner membranes. The organization of the anchovy cones is compared with that of other vertebrates. It is suggested that the cone unit may be a two channel analyser for the detection of plane polarized light and function in conjunction with the overlying reflector of regularly arranged platelets.

Behavioural investigation of polarisation sensitivity in the Japanese quail (Coturnix coturnix japonica) and the European starling(Sturnus vulgaris)

“…The bay anchovy, Anchoa mitchilli, and the broad-striped anchovy, Anchoa hepsetus, have bifid cone photoreceptors in which the array of visual pigmentcontaining lamellae are orientated at right angles in the two parts of the cone, and thus they are potentially able to analyse the angle of plane polarised light (Fineran and Nicol, 1978; reviewed by Locket, 1999). Such bifid cones have also been found in the black-sea anchovy, Engraulis encrasicholus (Zueva and Govardovskii, 1991).…”

Teleost polarization vision: how it might work and what it might be good for

“…Anchovies have two cone types, short (bifid) and long cones, both of which have a peak sensitivity, or l max , of 540 nm. These photoreceptors are spatially arranged in the photoreceptor layer so that the plane of orientation of their axial disc membranes is orthogonal, providing sensitivity to two polarization directions [8,9,16]. Other polarization-sensitive vertebrates that have been investigated do not show such specializations in the outer segment of photoreceptors.…”

“…The cone photoreceptors of some engraulids have disc membranes that are axially oriented and thus are distinct from all other vertebrate rods and cones that have disc membranes that are transversely oriented in the outer segment ( [16] (bay anchovy-Anchoa mitchilli); [9] (northern anchovy-Engraulis mordax); [8] (bay anchovy-A. mitchilli)).…”

Do cephalopods communicate using polarized light reflections from their skin?

“…However, there have been suggestions that polarization sensitivity in fish may be independent of UV-sensitive cones, such as in anchovies (Fineran and Nicol, 1976;Fineran and Nicol, 1978). Double cones may also provide a method of polarization detection that would include wavebands in the visible part of the spectrum (Cameron and Pugh, 1991;Flamarique et al, 1998).…”