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Changes in the Visual Cell Layer of the Duplex Retina During Growth of the Eye of a Deep‐sea Teleost, Gempylus serpens Cuvier, 1829
Acta Zoologica
Abstract
Ontogenetic changes in the visual cell layer of the duplex retina during growth of the eye of the deep-sea teleost Gempylus serpens, the snake mackerel, are illustrated by comparing the retina of a small specimen with that of a previously studied adult fish.
The small specimen has tightly packed cones spanning the whole width of the visual cell layer and small rods situated in its vitread part. Over most of the retina the cone population consists of single cones arranged in a very regular hexagonal mosaic. The temporalmost retina has a cone population consisting mainly of twin cones arranged in meridional rows.
Growth of the eye is associated with an increase in the thickness of the visual cell layer and the density of rods and a total elimination of the densely packed single cones, the retina of the adult fish possessing only a temporally located population of double cones.
The radical differences between the retina of the small and adult snake mackerel are probably associated with the different light regimes encountered by small and large specimens.
... Given this phylogenetic connection to the deep-sea, it is not surprising that some aspects of their visual development were comparable to deep-sea fishes while others more closely resembled shallow-water fishes. In terms of the cones, a steep decline in densities was evident during development (Fig. 3, Table 3) and the adult population was mainly composed of double cones, similar to the situation reported for some deep-sea fishes (Boehlert, 1979;Munk, 1990;de Busserolles et al., 2021). However, holocentrids retained cones in all retinal regions throughout life, whereas these are often lost at early developmental stages (Bozzano et al., 2007) or become restricted to certain retinal regions (Munk, 1990) in some deep-sea fishes. ...
... In terms of the cones, a steep decline in densities was evident during development (Fig. 3, Table 3) and the adult population was mainly composed of double cones, similar to the situation reported for some deep-sea fishes (Boehlert, 1979;Munk, 1990;de Busserolles et al., 2021). However, holocentrids retained cones in all retinal regions throughout life, whereas these are often lost at early developmental stages (Bozzano et al., 2007) or become restricted to certain retinal regions (Munk, 1990) in some deep-sea fishes. With respect to rods, adult holocentrids (particularly in Myripristinae) possessed peak densities that rival those of some deep-sea fishes (e.g. ...
Ontogenetic changes in the habitats and lifestyles of animals are often reflected in their visual systems. Coral reef fishes start life in the shallow open ocean but inhabit the reef as juveniles and adults. Alongside this change in habitat, some species also change lifestyles and become nocturnal. However, it is not fully understood how the visual systems of nocturnal reef fishes develop and adapt to these significant ecological shifts over their lives. Therefore, we used a histological approach to examine visual development in the nocturnal coral reef fish family, Holocentridae. We examined seven representative species spanning both subfamilies, Holocentrinae (squirrelfishes) and Myripristinae (soldierfishes). Pre-settlement larvae showed strong adaptation for photopic vision with high cone densities and had also started to develop a multibank retina (i.e., multiple rod layers), with up to two rod banks present. At reef settlement, holocentrids showed increased investment in their scotopic visual system, with higher rod densities and higher summation of rods onto the ganglion cell layer. By adulthood, they had well-developed scotopic vision with a highly rod-dominated multibank retina comprising 5-17 rod banks and enhanced summation of rods onto the ganglion cell layer. Lastly, the ecological demands of the two subfamilies were similar throughout their lives, yet their visual systems differed after settlement, with Myripristinae showing a more pronounced investment in scotopic vision than Holocentrinae. Thus, it is likely that both ecology and phylogeny contribute to the development of the holocentrid visual system.
... In adults, species with pure rod retinas tend to only express rod opsin(s) (Douglas et al. 2016;Musilova et al. 2019a), albeit two species of pearlsides (Maurolicus spp.) have been found to express cone-specific genes (i.e., cone transduction pathway and opsin genes) inside rod-looking cells (de Busserolles et al. 2017). It remains unknown whether deep-sea fishes that have a low proportion of cone photoreceptors as adults (Munk 1990;Collin et al. 1998;Bozzano et al. 2007;Pointer et al. 2007;Biagioni et al. 2016) also express cone-specific genes at any stages of their lives or whether these fishes rely on the rod machinery alone. To investigate whether the retinal development in deep-sea fishes follows a similar cone-to-rod molecular pathway as found in other vertebrates or whether some species start their lives with the rod pathway activated, we set out to sequence the retinal transcriptomes of 20 deep-sea fish species, including the larval stages in ten species, belonging to eight different teleost orders (Argentiniformes, Aulopiformes, Beryciformes, Myctophiformes, Pempheriformes, Scombriformes, Stomiiformes, and Trachichthyiformes). ...
Vertebrates use cone cells in the retina for color vision and rod cells to see in dim light. Many deep-sea fishes have adapted to their environment to have only rod cells in the retina, while both rod and cone genes are still preserved in their genomes. As deep-sea fish larvae start their lives in the shallow, and only later submerge to the depth, they have to cope with diverse environmental conditions during ontogeny. Using a comparative transcriptomic approach in 20 deep-sea fish species from eight teleost orders, we report on a developmental cone-to-rod switch. While adults mostly rely on rod opsin (RH1) for vision in dim light, larvae almost exclusively express middle-wavelength-sensitive (“green”) cone opsins (RH2) in their retinas. The phototransduction cascade genes follow a similar ontogenetic pattern of cone—followed by rod-specific gene expression in most species, except for the pearleye and sabretooth (Aulopiformes), in which the cone cascade remains dominant throughout development, casting doubts on the photoreceptor cell identity. By inspecting the whole genomes of five deep-sea species (four of them sequenced within this study: Idiacanthus fasciola, Chauliodus sloani; Stomiiformes; Coccorella atlantica, and Scopelarchus michaelsarsi; Aulopiformes), we found that they possess one or two copies of the rod RH1 opsin gene, and up to seven copies of the cone RH2 opsin genes in their genomes, while other cone opsin classes have been mostly lost. Our findings hence provide molecular evidence for a limited opsin gene repertoire in deep-sea fishes and a conserved vertebrate pattern whereby cone photoreceptors develop first and rod photoreceptors are added only at later developmental stages.
... The presence of cones in the retina of deep-sea fishes is, however, not uncommon. Munk (1965Munk ( , 1981Munk ( , 1982Munk ( , 1984Munk ( , 1989Munk ( , 1990 has investigated a number of species, which possess cones, with some regions of the retina even being described as pure-cone. The most definitive morphological distinction between rods and cones comes from the nature of the outer segment. ...
Marine hatchetfishes, Argyropelecus spp., are one of the 14 genera of mesopelagic teleosts, which possess tubular eyes. The tubular eyes are positioned dorsally on the head and consist of a main retina, which subtends a large dorsal binocular field, and an accessory retina, which subtends the lateral monocular visual field. The topographic distribution of photoreceptors in the retina of Argyropelecus sladeni, Argyropelecus affinis, and Argyropelecus aculeatus was determined using a random, unbiased and systematic stereological approach, which consistently revealed a region of high density (area centralis) in the central region of the main retina (up to a peak of 96,000 receptors per mm²) and a relatively homogeneous density of photoreceptors in the accessory retina (of ~20,000 receptors per mm²). The position of the area centralis in the main retina indicates this retinal region subserves greater spatial resolution in the center of the dorsal binocular visual field. Light microscopy and transmission electron microscopy also revealed the presence of multiple photoreceptor types (two rod-like and one cone-like) based on the size and shape of the inner and outer segments and ultrastructural differences in the ellipsoidal region. The presence of multiple photoreceptor types in these tubular-eyed, mesopelagic hatchetfishes may reflect the need for the visual system to function under different lighting conditions during vertical migratory behavior, especially given their unique dorsally-facing eyes.
Changes in retinal morphology during growth were studied in three species ofMerluccius, i.e.,M. capensis Castelnau andM. paradoxus Franca from the southeastern Atlantic andM. merluccius L. from the Mediterranean. The structure of both the rod and the cone systems showed both inter-and intraspecific differences which reflect functional differences in both sensitivity and viusal acuity. The interspecific differences in estimated sensitivity recorded were related to differences in depth distribution and the extent of nighttime feeding activity. In the three species studied, the increase in sensitivity and visual acuity with growth was associated with the increase in habitat depth and changes in diet. The results obtained indicated that the morphology of the visual systems changes during the lifetime of the fish, adapting continuously to environmental conditions and behaviour.
Changes in retinal structure during settlement were investigated in four species of tropical reef-associated teleost fishes with differing periods of planktonic duration and post-settlement lifestyles. They were: Apogon doederleini (Apogonidae), a nocturnal planktivore; Stethojulis strigiventer (Labridae), a diurnal microcarnivore; Upeneus tragula (Mullidae), a carnivore which uses chin barbels to disturb invertebrates from the sediment; and Pomacentrus moluccensis (Pomacentridae), a diurnal herbivorous planktivore. The densities of cones, rods, cells in the inner nuclear layer and cells in the ganglion cell layer were estimated in a size range of each species. Visual acuity was calculated using cone densities and lens diameter. The ontogenetic sequence of changes in cell density was similar in all species but interspecific variation in the timing and rates of change was found and could be related to lifestyle. For example, cone densities decreased and rod densities increased most rapidly in the nocturnal species, A. doederleini, during settlement. In contrast, high cone densities were maintained in the species adopting a diurnal lifestyle. Theoretical visual acuity was found to increase rapidly as lens size increased, but was similar for all species at similar lens sizes, indicating the importance of larger eye size as a means for improving resolution during early stages of eye growth. It was concluded that for the species undergoing abrupt lifestyle changes at settlement, structural re-organisation of the retina is important for the survival of the fish as they leave the pelagic environment and take up their reef-associated lifestyle.
We examined the retinal cone topography in sexually mature individuals from four species of Pacific salmonid fishes by using semithin plastic sections. We identified variations in cone density and cone arrangements and noted the presence of putative ultraviolet (UV) cones. Putative UV cones were found over an area extending dorsotemporally from the center of the retina. Because most of the putative UV cones are believed to disappear in early ontogeny, their presence over a large proportion (15-20%) of the surface area of the adult retina suggests that they may be reincorporated prior to or at sexual maturity, at least in rainbow trout. Cone density varied across the retina, with highest values at the peripheral margin. Relatively high densities were observed ventrotemporally (in all specimens) and, to a lesser extent, dorsonasally (7 of 11 specimens). The higher cone density in the ventrotemporal retina may represent a retinal specialization in the part of the visual field located above and in front of the animal. Lowest cone densities were found dorsocentrally and coincided approximately with the distribution of putative UV cones, raising the possibility that these cones may not be used in visual tasks requiring the higher visual acuity normally associated with higher cone densities. We also report a novel cone arrangement that consists of rows of double cones inserted between rows composed of single-double cone pairs alternating in position.
All vertebrate eyes have evolved from those of common underwater living ancestors and consequently are strikingly similar structures which form an image with a single lens. In contrast, invertebrates have a rich variety of eye types which form images in one of three ways: with single lenses, multiple lenses, or mirrors (Land, 1984). Since eyes must obey fundamental optical laws, physical constraints on eye design and structure provide the most straightforward means of understanding the adaptive value of ocular specializations. Using these physical constraints, inferences about the selective forces that have undoubtedly “shaped” eyes can be made with some confidence, particularly in the study of aquatic eyes. In contrast, in the analysis of ocular development there is no corresponding a priori knowledge of fundamental constraints to aid in interpreting these developmental processes. Developmental similarities themselves must serve to guide our understanding of these processes. Phylogenetic comparisons offer significant advantages because the modifications that have occurred during evolutionary time are carried in organisms and are most evident during development.
The topographical distribution of cones and rods in the tree shrew retina was analysed quantitatively in whole-mounted retinae and horizontal semithin sections stained with cresyl violet or toluidine blue. The outer nuclear layer consists of a single layer of photoreceptor nuclei with the rod nuclei slightly displaced towards the outer plexiform layer. This facilitated quantification of the photoreceptor populations. The density of cones ranges from 12,000/mm2 in the peripheral retina to a maximum of 36,000/mm2 in the inferior retina. Unlike ganglion cell density, the density of cones does not peak in the temporal retina. Rod density, between 500/mm2 and 3,500/mm2, also peaks in the inferior retina, but not in the same region as cone density. Rods constitute from 1 to 14% of the photoreceptor population, depending on retinal location, and have a local minimum at the central area. Amongst the cones a regularly arrayed subpopulation of presumed blue-sensitive cones is distinguished by its special staining properties. These cones constitute between 4 and 10% of the cone population depending on retinal location. A second, irregularly spaced, subpopulation of possibly pathological cones is also described.
The vertebrate eye originally evolved as an underwater visual organ; thus, all vertebrate eyes share a common set of structural properties. This is in striking contrast to the enormous variety of eye types found among invertebrates. Despite the fundamentally similar ocular architecture that exists throughout vertebrate phylogeny, there are still significant differences among eyes. Specifically, fishes, which comprise more than half the extant vertebrate species, have eyes that grow throughout their lifetimes. The advantages of a larger eye are the greater light-capturing ability for deep-sea fish and higher acuity for surface dwellers (for details, see Fernald, 1988).
The world’s oceans cover some 70% of the surface of the globe, and of this area 75% is deeper than 3000 m. Unaided, man can explore only the surface and edges of this mass of water; he requires diverse probes and samplers to investigate the habitat of deep-sea fishes.
The pure rod retina of mature Chauliodus sloani contains up to five
banks of rods, but that of small specimens contains only one bank. New
banks are added progressively as the fish grows. The size of the retinal
cells remains approximately constant throughout the range, but, as the
retinal thickness increases with growth and new banks are added, the
density of nuclei in the outer nuclear layer increases. The density of
total rods increases as new banks are added, but that of the vitread
bank remains constant or falls slightly. The density of ganglion cells
falls with growth, the estimated total in the retina rising to a maximum
by about 100 mm standard length. Estimates of convergence ratio of total
rods to total ganglion cells increase from about 7:1 in the smallest to
about 200:1 in the largest specimens. Implications of the findings for
the development and function of the multiple-bank retina are discussed.
The eye of the deep-sea teleost Lestidiops affinis has been examined primarily by light microscopy and found to possess a duplex retina consisting of two main divisions, a pure-cone and a pure-rod region, with a narrow zone of transition, possessing both cones and rods, joining the two. The pure-cone region is located in the temporal (caudal) part of the retina subserving binocular vision in the rostral direction. It has an area temporalis retinae with particularly long and densely packed single cones arranged in a regular hexagonal mosaic. Joined (double or twin) cones have not been recognized with certainty in the pure-cone region. The pure-rod region, comprising the larger part of the retina, contains rods grouped in bundles separated by retinal pigment epithelium (RPE) processes with pigmented cores. The synaptic endings of the rods are arranged in separate clusters in the outer plexiform layer, there being apparently a separate rod pedicle cluster beneath (vitread to) each rod bundle. Structural comparisons with certain other deep-sea teleosts suggest the likely presence of a retinal tapetum in L. affinis, i.e. each single cone or rod bundle is situated in a reflecting pit formed by the RPE, with a discrete reflector apposed to the tip of each cone outer segment and the tips of the outer segments of each square-cut rod bundle.
In the present paper a survey is made of the facts known about the cone types present in teleosts, their distribution among the fishes and their arrangement in the retina. The reports found in the literature have been collected and compared with those obtained from the author's studies of the cones of a number of fishes. The results obtained from this investigation are shown in the summary table pp. 225-229. Some aspects on the classification of the cone types and the cone mosaics are discussed. The single cones are classified-according to their general appearance and their positions in the mosaic-into long (=central) and short (=additional) single cones, the latter ones often being rare or absent. Within the double cones, a wide variety of equal and double ones have been found, some of which are shown in the drawings, fig. 32. Some evidence is presented that cone types are correlated to the phylogeny of the fish, but a more detailed discussion concerning these problems is not considered profitable until more data about the cone types and their variation within the retina are available. The triple cones and the quadruple cones are both found to be represented by two main types, but their distribution among the fishes is still very poorly known. The different types of cone mosaics and their relation to each other are discussed as well as their relation to the phylogeny and the ecology of the fishes. The main type of mosaic which can be developed in fishes is considered correlated with the phylogeny of the taxonomical unit to which it belongs; the degree of accomplishment of this type of mosaic in a certain species is found to be dependent on its ecology. Thus, a regular mosaic is found in the retina-or parts of the retina-of fishes which rely to a great extent on vision, but more irregular or resolved mosaics are found in fishes having nocturnal habits or making more use of other senses than of vision. The demand for more thorough studies of the cone types as well as the cone mosaics, using tangential sections and studying the variation within the retina, is emphasized.
1.
Da die Klassifizierung der Zapfentypen aufgrund von morphologischen Merkmalen schwierig ist, werden:
a)
die Entfernung der Zapfenellipsoide von der Membrana limitans externa;
b)
die Stellung der Zapfen innerhalb des Mosaiks als weitere Kriterien herangezogen.
2.
Die Doppelzapfen konnen in parallelen Reihen stehen (Reihenmuster) oder im Quadrat angeordnet sein (Quadrat- oder Rechteckmuster). In beiden Mustern knnen zu den Doppelzapfen em. oder zwei Einzelzapfentypen hinzutreten.
3.
Die beiden Mustertypen stehen in einem ontogenetischen Zusammenhang: An der Ora serrata werden alle Doppelzapfen in parallelen Reihen angelegt and erst im Retinainneren bei den entsprechenden Arten zu Rechtecken umgeordnet.
4.
Bei Betta and Nannacara stehen innerhalb des Doppelzapfenquadrats jeweils vier Stbchen; bei einigen anderen Arten umgeben bis zu acht Stabchen kranzartig die Einzelzapfen. In den moisten Fllen sind die Stbchen zahlreicher als die Zapfen.
5.
Wahrscheinlich besteht ein Zusammenhang zwischen Augendurchmesser bzw. Alter and der regelmigen Anordnung Bowie der Zahl der Stbchen.
6.
Es werden verschiedene morphologische Zelltypen der drei Horizontalenreihen beschrieben and ihr Vorkommen bei bisher von anderen Autoren (besonders Cajal) untersuchten Arten errtert.
7.
Aufgrund von morphologischen Merkmalen kann nicht entschieden werden, ob die Horizontalen Neuronen oder Glia-Elemente sind.
8.
Die Reihen der scleraden Horizontalen verlaufen — unabhngig vom Typ des Doppelzapfenmosaiks — parallel zu den Einzelzapfenreihen.
9.
Die Einzelzapfenabstnde and die Entfernung zwischen den Kernen der ueren Horizontalen sind gleich gro.
10.
Die mittleren and inneren Horizontalen sind nur dann regelmig angeordnet, wenn sie aus lappig-sternfrmigen Zellen bestehen.
11.
Bei Rechteck- und Streifenmustern ist die Anzahl der Horizontalenschichten ebenso gro wie die der Zapfentypen.
12.
Die relativen Zahlenverhltnisse von Doppelzapfen zu Einzelzapfentypen bzw. ueren zu mittleren and inneren Horizontalen zeigen bei vielen Arten eine gute bereinstimmung. In absoluten Zahlen ausgedrckt kommen auf jede Horizontale 2 Zapfen. Nur die inneren Horizontalen weichen bei einigen Arten von dieser Regel ab.
13.
Beim Vergleich verschiedener Rechteckmuster ergibt sich ein zahlenmiger Zusammenhang zwischen mittleren Horizontalen and zentralen Einzelzapfen, vitreaden Horizontalen and eckstndigen Einzelzapfen Bowie scleraden Horizontalen und Doppelzapfen.
14.
Die Beziehung zwischen der Anzahl der Zapfentypen and der Anzahl der Horizontalenreihen Bowie deren Bedeutung fur das Farbensehen wird durch elektrophysiologische Befunde von Svaetichin besttigt.
15.
Es werden Funktionsmodelle des Bewegungssehens and der lateralen Inhibition aufgrund der Lagebeziehung zwischen Zapfen- und Horizontalenmuster diskutiert. Experimentelle Befunde zu diesen Modellen liegen bisher nicht vor.
1.
Since the classification of the cone types on morphological features is difficult
a)
the distance of the cone-inner-segment from the outer limiting membrane
b)
the position of the cones within the mosaic are used as further criteria.
2.
The double cones are either arranged in parallel rows (row-mosaic) or in square units (square mosaic). In both types one or two single cones may be added to the basic pattern.
3.
There is an ontogenetic relation between the two mosaic types: Near the Ora serrata, all double cones are placed in parallel rows and only in the more central part of the bulbus of certain species are they arranged in squares.
4.
In Bettta and Nannacara 4 rods are enclosed in every square unit; in some other species there are up to 8 rods surrounding the single cones. In most cases rods are more numerous than cones.
5.
Probably there is a relationship between the age and diameter of the eye and the regular arrangement resp. the number of the rods.
6.
The different morphological types within the three layers of horizontal cells are described. Their occurence and distribution is compared to the findings of other authors (chiefly Cajal).
7.
Based on morphological characteristics one cannot determine whether the horizontal cells are neurons or glia elements.
8.
The rows of the sclerad horizontal cells run parallel to the rows of single cones without respect to the type of double cone mosaic.
9.
There is an equal distance between the nuclei of the single cones and between the nuclei of the outer horizontal cells.
10.
The middle and inner horizontal cells are arranged regularly only when they consist of lobed stellar shaped cells.
11.
In square and row mosaics the number of horizontal cell layers equals the number of cone types.
12.
The relative ratio of double cones to single cones is in good agreement with that of sclerad to intermediary and vitread horizontal cells. In absolute figures there are 2 cones for every horizontal cell. Only the vitread horizontal cells of a few species do not fit this rule.
13.
If one compares different square mosaics, one finds a quantitative relation between intermediary horizontal cells and accessory single cones as well as between sclerad horizontal cells and double cones.
14.
The correlation between the number of cone types and the number of horizontal cell layers and its functional significance for colour vision is confirmed by the electrophysiological data of Svaetichin.
15.
Several functional models of movement perception and lateral inhibition are discussed on the basis of a parallel arrangement of the cone—and the horizontal cell mosaic. Until now there are no experimental data confirming these models.
A population of mitotic cells that produce new neurons has recently been discovered in the layer of photoreceptors in retinas of several species of larval and adult fish. These cells generate new rods which are inserted into the photoreceptor mosaic at locations scattered across the entire expanse of the differentiated retina. Subsequently these new rods establish synaptic connections with retinal neurons already present. The continued production of rods in the fish is apparently needed to maintain visual sensitivity during postembryonic growth of the eye. Peer Reviewed http://deepblue.lib.umich.edu/bitstream/2027.42/25790/1/0000352.pdf
Retinal growth in young Sebastes diploproa involves the succession of three distinct cone patterns. Development of the final pattern with the loss of single cones occurs in close temporal association with a permanent migration from the surface to deep water. The results suggest that loss of single cones depends upon the change in environment and that the loss occurs through fusion to double elements.
The manner in which new cells are added to the growing adult goldfish retina was examined using 3H-thymidine radioautography. Cell proliferation leading to the formation of neurons is restricted to the retinal margin at the ora terminalis. New retina is added in concentric rings, with slightly more growth dorsonasally. The rate of cell addition is variable, averaging 12,000 cells/day. These new cells account for about 20% of the total increase in retinal area; the remaining 80% is due to hypertrophy, or expansion, of the retina. In contrast to all of the other retinal cells, the rods do not appear to participate in the retinal expansion. This hypothesized immobility of the rods would create a shearing strain between the retinal layers resulting in a shift in their position relative to the other cells. Were they to maintain synaptic contacts with the same horizontal and bipolar cells, the rod axons would have to be elongated peripherally or the post-synaptic cell dendrites displaced centrally. Since neurons with this morphology have not been found in the goldfish retina, these observations suggest that the rods must be changing their synaptic connections as the retina grows.
Microspectrophotometric analysis of the visual receptors of "yearling" brown trout, Salmo trutta, revealed three cone types, double cones with visual pigments absorbing maximally at about 600 and 535 nm, and two types of single cone with lambda max at about 440 and 355 nm. Two-year-old fish did not possess the u.v. cone cells. Microscopical analysis of the cone mosaic in "yearling" trout showed a square pattern of double cones with a central single cone and corner single cones, but in two-year-old trout the corner cones were absent. It is concluded that u.v. sensitivity is derived from the corner cones of the mosaic, and that it is only present in young trout.
We previously showed that the brown trout possesses UV-sensitive cones in its retina that are lost in 2-year-old fish. However, present investigations reveal that in the narrow growth zone along the periphery and the ventral embryonic fissure, the formation of these cones continues in trout and salmon.
Using standard paraffin technique the addition of new cells in crucian carp retinas was examined. Between eye diameters 4.4 and 10.0 mm the number of ganglion cells increases from 103,000 to 205,000, INL cells from 1.5 to 3 million, cones from 250,000 to 900,000, and rods from 2 to 9 million. Concomitantly retinal area increases fivefold and the cell densities decrease by 37% for the cones, 57% for th e INL cells, and 58% for the ganglion cells, while the rod density remains stable.
In relation to the rods the cell ratios at different retinal loci undergo marked changes during growth. The contributions to retinal growth by addition of new neurons and by expansion of the retina have been determined for the different retinal layers. The layer of rods grows exclusively by addition of new rod mosaic. In the cone layer 81% of growth is due to addition of new cone mosaic. In the inner nuclear layer (INL) 56% of growth is due to addition of new cells and in the ganglion cell layer 52% is due to cell addition. In each case retinal expansion accounts for the remainder of increase in retinal area.
On morphological grounds six cone types can be found in the crucian carp retina. Their ratios are constant during retinal growth and at different retinal loci.
Organization of the cone cells in the retinae of some teleosts in relation to their feeding habits
- I.-B Ahlbert
The eyes of some ceratioid fishes
- Munk O.
On the cones of the mesopelagic teleost Trachipterus trachypterus (Gmelin, 1789)
- Munk O.
Retinal cones of the snake mackerel, Gempylus serpens Cuvier, 1829
- Munk O.
Material on the distribution and biology of the snake mackerel, Gempylus serpens Cuv. (Pisces, Gempylidae), in the Pacific and Indian oceans
- Parin N. V.