The position of the retinal area centralis changes with age in Champsocephalus gunnari (Channichthyidae), a predatory fish from coastal Antarctic waters

Histological examinations of the topographical distribution and the area of highest density (the area centralis: AC) of presumed retinal ganglion cells found in the retina in 0- to 6-year-old Champsocephalus gunnari revealed differences between younger and older fish. Individuals of up to 2 years of age had the AC in the temporal retina, whereas in 3-, 4-, 5- and 6-year-old fish it was positioned in the ventro-temporal region of the retina. The main visual axis in the pitch plane of C. gunnari was shown to shift from facing forward to an upward-forward direction during growth, corresponding to the habitat change in this species from pelagic to benthic. Moreover, the AC in 0- to 3-year-old fish was near the retinal periphery, but displaced towards the inner retina in 4- to 6-year-old fish. This means that the visual axis in the horizontal plane of the younger fish was directed towards the frontal sector of vision, while in the older fish a slightly more lateral position was favoured. Therefore, younger fish can be expected to possess superior binocular vision when it comes to prey closely in front of them, but in older fish it seems more important to have a wider visual field to detect prey (and possibly predators) within a greater volume of water.     

New evidence for the role of heterochrony in the repeated evolution of cichlid opsin expression

SUMMARY Lake Malawi (LM) cichlids have undergone heterochronic shifts in the expression of their cone opsin genes, the genes responsible for color vision. These shifts have generated species with short-, middle-, and long-wavelength-sensitive cone photoreceptors and visual systems. However, it is unclear when during the evolution of African cichlids these shifts occurred, or whether they could account for similar short- and middle-wavelength-sensitive profiles among unrelated cichlids in Lake Tanganyika (LT). To address these questions, we surveyed opsin expression in developing fry of two African cichlids, Astatotilapia burtoni from LT and Melanochromis auratus from LM. We found that A. burtoni expresses a series of three different single-cone opsins over the course of development, while M. auratus exhibits variation in the expression of only two. Neither A. burtoni nor M. auratus exhibits much variation in the expression of its double-cone opsins. These patterns reveal that A. burtoni exhibits progressive development in the sensitivity of its single-cone photoreceptors, but direct development in the sensitivity of its double-cone photoreceptors. M. auratus exhibits neotenic development in the sensitivity of both photoreceptor sets. Given the intermediate phylogenetic placement of A. burtoni between cichlids from LT and LM, our results suggest that the ancestor of LM's cichlids exhibited a progressive developmental pattern of opsin expression. These results indicate that the heterochronic shifts which produced the short- and middle-wavelength-sensitive profiles of LM's cichlids occurred recently, and suggest that the presence of similar profiles among LT's cichlids are due to parallel heterochronic shifts.     

Polarized-light sensitivity in rainbow trout (Oncorhynchus mykiss): characterization from multi-unit responses in the optic nerve

Integrated spike activity of axons from the optic nerve was measured in an investigation of the e-vector sensitive mechanism underlying the ability of rainbow trout (Oncorhynchus mykiss) for orientation in downwelling, linearly-polarized light. In anaesthetized, immobilized fish, one eye was exposed to incremental light flashes which were superimposed over closely controlled background conditions. Under scotopic and various photopic conditions, intensity/response curves were generated from the on-response of the optic nerve. Relative sensitivity curves were then obtained as a function of e-vector direction for the 5 kinds of receptor cells in this trout's retina: rods, ultraviolet cones (UV), short wavelength cones (S), medium wavelength cones (M), and long wavelength cones (L).Under scotopic conditions, no sensitivity to e-vector was apparent: thus, rods do not mediate polarization sensitivity. Under photopic conditions, parr weighing 8–10 g exhibited e-vector sensitivity in two orthogonal channels. A UV stimulus (380 nm) on a white background evoked a three-peaked response (0°, 90°, and 180°) to the e-vector orientations presented in 30° increments between 0° and 180°. In contrast, when the background was illuminated with appropriate short and long wavelength cut-off filters, M-and L-cones showed maximum responses only to the horizontal (90°) plane whether they were stimulated at their -absorption band or their -absorption band in the near UV. Isolated UV-cones gave maximum responses to the vertical (0° and 180°) e-vector, thus corresponding to a second channel. The blue sensitive, S-cones, did not show evidence of polarization sensitivity. As well, no evidence of the polarization sensitivity was observed under UV isolating background conditions in larger individuals, 50–78 g smolts, although the other cone mechanisms responded as in smaller individuals.     

生物组织X光照片的层析合成法的研究——Ⅱ.优化层片特性的模拟

在圆层析合成法中,我们提出了两种X光扫描采样的方法.一种是以零阶贝塞尔函数为窗函数,采用单个的采样园锥.另一种是以圆长球函数为窗函数,用Fourier-Bessel级数展开的系数为权,采用多重采样圆锥.在适当选择窗函数的参数下,给出了采样几何学的设计及对不同窗函数的衰减特性进行了模拟.     

A cellular basis for polarized-light vision in rainbow trout

Polarized light sensitivity was examined in single units of the rainbow trout (Oncorhynchus mykiss) torus semicircularis, a sub-tectal visual area with a high degree of ultraviolet sensitivity. First, chromatically isolated torus units with inputs from each of the four cone mechanisms found in the trout visual system were separately examined for e-vector sensitivity. UV ON-response units showed polarization sensitivity for vertical ly (0° and 180°) polarized stimuli, while ON-response units of the short, middle and long cone mechanisms were not polarization sensitive. No OFF-response units of the UV or short cone mechanism were observed, but OFF-response units of the middle and long cone mechanisms show polarization sensitivity for horizontally (90°) polarized stimuli. Second, e-vector sensitivity was observed in color-coded units which received inputs from more than one cone mechanism and showed different sign responses (ON or OFF) at different points of the spectral sensitivity curve. Biphasic units which had ON input from the UV cone mechanism and OFF inputs from the middle and long cone mechanisms showed polarization opponency. This opponency was observed with a 380 nm stimulus when the threshold sensitivities of the alpha-band absorption peak of the UV mechanism and the beta-band absorption peak of the middle and long cone mechanisms were equal. We believe that biphasic torus units provide a possible cellular basis for polarized light vision in rainbow trout.Abbreviations UV ultraviolet - S short - M middle - L long - PS polarization sensitivity - TS torus semicircularis - ONR optic nerve response     

Optic tract cells projecting to the retina in the teleost,Pantodon buchholzi

Summary Horseradish peroxidase was employed to trace retino-fugal and retino-petal connections in the teleost fish, Pantodon buchholzi. Most of the reciprocal connections found were within the range also observed in previously studied species of teleosts. Of particular interest is the discovery of cells located within the optic tract and projecting to the retina. These neurons were investigated electron microscopically.     

The common white sucker (Catostomus commersoni ): a fish with ultraviolet sensitivity that lacks polarization sensitivity

Two families of fishes, the Cyprinidae and Salmonidae, exhibit ultraviolet sensitivity and polarization sensitivity (i.e., differential sensitivity to the orientation of the electric field of polarized light). Both of these families possess a square arrangement of double cones and/or their dividing partitions in the centro-temporal retina, an area where polarization sensitivity has been tested for and found. To correlate the presence of an ordered cone mosaic in the centro-temporal retina with polarization sensitivity in ultraviolet-sensitive fishes, we examined the visual system of the common white sucker (Catostomus commersoni) and compared it to those of the above-mentioned families. We found that the common white sucker possesses four cone-mediated neural mechanisms similar to those in cyprinids and salmonids, but it does not exhibit polarization sensitivity. In addition, unlike cyprinids and salmonids, the common white sucker shows a random cone mosaic in the centro-temporal retina. These results suggest that polarization sensitivity in ultraviolet-sensitive fishes requires an ordered double-cone mosaic in this area of the retina. Accepted: 19 July 1997     

Larval size constraints determine directional ontogenetic shifts in the visual system of teleosts1

We summarize characteristic sequences of morphological change in the teleost visual system from larvae to large adults at the level of the retina, the optic tract and the optic tectum. These shifts include sizes and ratios of cone and rod receptor cells, sizes and types of retinal ganglion cells and optic tract fibers as well as features of the optic tectum. Teleost larvae are the smallest vertebrates known. We suggest that the utilization of color contrasts as an adaptive benefit dictates the starting point of morophological development, which is a pure cone retina in most fish larvae. The direction of morphological and functional shifts in the teleost visual system during growth is determined by continuous retinal stretch, which allows for improving visual abilities. The larval visual system probably provides just adequate photopic (cone-)acuity for plankton feeding, but limited space in the retina hampers optimization of both, photopic resolving power and sensitivity Limited space also Irevents the simultaneous development of the scotopic (rod-)system. Over a wide range of body sizes, morphological parameters change, photopic and scotopic resolving power, acuity and sensitivity improve. Size constraints in the teleost visual system and lifefong shifts in sensory capacities are discussed with respect to ecology and the niche concept.     

Diet of two icefish species from the South Shetland Islands and Elephant Island,<Emphasis Type="Italic"> Champsocephalus gunnari</Emphasis> and<Emphasis Type="Italic"> Chaenocephalus aceratus</Emphasis>

The summer diet of two species of icefishes (Channichthyidae) from the South Shetland Islands and Elephant Island, Champsocephalus gunnari and Chaenocephalus aceratus, was investigated from 2001 to 2003. Champsocephalus gunnari fed almost exclusively on krill (Euphausia superba) in all years. The importance of other taxa (Themisto gaudichaudii, mysids, myctophids) in the diet was negligible. The average feeding rate of Champsocephalus gunnari inferred from an exponential gastric evacuation model was between 1.0 and 1.5% body weight per day. Most of the stomachs of Chaenocephalus aceratus were empty. Stomachs with food contained mainly krill, mysids and fish. Among the fish taken, locally abundant species formed the bulk of the diet: Gobionotothen gibberifrons in 2001, Lepidonotothen larseni and Champsocephalus gunnari in 2002 and L. larseni in 2003. An ontogenetic shift in feeding preference of Chaenocephalus aceratus was observed: fish smaller than 30 cm fed on krill and mysids, while larger animals relied primarily on fish.     

Conservation of antigen 3G6: A crystalline cone constitutent in the compound eye of arthropods

A monoclonal antibody (MAb), 3G6, highly selective for neuropil glia in the CNS of the house cricket Acheta domesticus, also demonstrates remarkable selectivity for the nonneuronal crystalline cone cells of the compound eye. MAb 3G6 labels cone cells in eucone eyes throughout Insecta, from ancestral forms such as the bristle tail to the more recent honeybee; eucone structures are also recognized in Crustacea. Analogous nonneural structures found in pseudocone or acone eyes also express detectable 3G6 immunoreactivity. Immunoblot analysis demonstrates that MAb 3G6 binds to similar M_r 85 kDa glycoproteins in the cricket CNS and retina, corresponding to the glial and crystalline cone forms of the antigen. Further, polypeptides of similar relative mass are also recognized in the eucone eye of the butterfly Pieris and the pseudocone eye of the fly Calliphora. The properties and function of glycoprotein 3G6 in the CNS and retina are yet to be explored. However, the finding that a unique antigen is highly conserved within the crystalline cone or analogous regions of the retina throughout the Arthropoda lends support at the molecular level to the notion that the arthropod compound eye has a monophyletic origin.     

Cues intrinsic to the retina induce nAchR gene expression during development

Recent studies of optic nerve regeneration in goldfish have indicated that the optic tectum plays an important role in modulating the induction of nicotinic acetylcholine receptor (nAChR) gene expression in regenerating retinal ganglion cells (Hieber, Agranoff, and Goldman, 1992, J. Neurochem. 58:1009–1015). These observations suggest that induction of these genes is regulated by brain target regions. The appearance of nAChR mRNA in the developing rat retina coincides with a time when ganglion cells are sending axons to their brain targets (Hoover and Goldman, 1992, Exp. Eye Res. 54:561–571). Might a mechanism similar to that seen during goldfish optic nerve regenerationalso mediate induction of nAChR gene expression during development of the mammalian retina? This possibility was tested by either transplanting embryonic rat retina to different brain regions, or explanting it to organ culture and assaying for nAChR gene expression. These studies showed that induction of the nAChR genes in developing rat retina is independent of the environment in which the retina develops. These results indicate that either the retinal microenvironment or a signal intrinsic to the retinal ganglion cell is responsible for this induction. © 1993 John Wiley & Sons, Inc.     

A distinct effect of transient and sustained upregulation of cellular factor XIII in the goldfish retina and optic nerve on optic nerve regeneration

Unlike in mammals, fish retinal ganglion cells (RGCs) have a capacity to repair their axons even after optic nerve transection. In our previous study, we isolated a tissue type transglutaminase (TG) from axotomized goldfish retina. The levels of retinal TG (TG(R)) mRNA increased in RGCs 1-6weeks after nerve injury to promote optic nerve regeneration both in vitro and in vivo. In the present study, we screened other types of TG using specific FITC-labeled substrate peptides to elucidate the implications for optic nerve regeneration. This screening showed that the activity of only cellular coagulation factor XIII (cFXIII) was increased in goldfish optic nerves just after nerve injury. We therefore cloned a full-length cDNA clone of FXIII A subunit (FXIII-A) and studied temporal changes of FXIII-A expression in goldfish optic nerve and retina during regeneration. FXIII-A mRNA was initially detected at the crush site of the optic nerve 1h after injury; it was further observed in the optic nerve and achieved sustained long-term expression (1-40days after nerve injury). The cells producing FXIII-A were astrocytes/microglial cells in the optic nerve. By contrast, the expression of FXIII-A mRNA and protein was upregulated in RGCs for a shorter time (3-10days after nerve injury). Overexpression of FXIII-A in RGCs achieved by lipofection induced significant neurite outgrowth from unprimed retina, but not from primed retina with pretreatment of nerve injury. Addition of extracts of optic nerves with injury induced significant neurite outgrowth from primed retina, but not from unprimed retina without pretreatment of nerve injury. The transient increase of cFXIII in RGCs promotes neurite sprouting from injured RGCs, whereas the sustained increase of cFXIII in optic nerves facilitates neurite elongation from regrowing axons.     

Retinal development in mandarinfish Siniperca chuatsi and morphological analysis of the photoreceptor layer

We describe the process of retinal development in mandarinfish Siniperca chuatsi from larvae to young fish. The developmental characteristics of the retinal structure and related cells were identified. Siniperca chuatsi were found to exhibit an altricial mode of retinal development that required considerable time to be completed after hatching. The retina was classed as a pure cone type during the early developmental stage. In the subsequent developmental stages, however, double cones gradually occupied the majority of the cone cells, while rod cells represented the majority of the photoreceptor cells. The outer segment (OS) of the rod cells were significantly longer compared with other morphological features, the OS of the two kinds of cone cells were significantly elongated and the diameters of the inner segment (IS) and OS of the double cone cells were significantly narrower in the later developmental stages. Combined with the scattered arrangement of cone cells at the different stages, the retina was found to have sacrificed a considerable part of visual acuity in the developmental process. The distribution of cone cells was observed to have gradually become regionalised during development. The findings of the present study also indicated that S. chuatsi have a high photosensitivity under dim light conditions as a result of specialised structures of the OS of photoreceptor cells and an increased number of rod cells. The loose arrangement of the cone mosaic presumably resulted in a poor imaging quality and, to some extent, the regionalisation of the cone-cell distribution compensated for the above shortcomings, which would enhance the ability of S. chuatsi to perceive targets in important directions for effective predation behaviour.     

Antibodies against pax6 immunostain amacrine and ganglion cells and neuronal progenitors,but not rod precursors,in the normal and regenerating retina of the goldfish

Pax6 is a developmental regulatory gene that plays a key role in the development of the embryonic brain, eye, and retina. This gene is also expressed in discrete groups of neurons within the adult brain. In this study, antibodies raised against a fusion protein from a zebra fish pax6 cDNA were used to investigate the expression of the pax6 gene in the mature, growing, and regenerating retina of the goldfish. On western blots of retinal proteins, the pax6 antibodies recognize a single band at the approximate size of the zebra fish pax6 protein. In retinal sections, the antibodies label the nuclei of mature amacrine and some ganglion cells. At the retinal margin, where neurogenesis and cellular differentiation continually occur in goldfish, the antibodies label neuronal progenitors and the newly postmitotic neurons. Following injury and during neuronal regeneration, the antibodies label mitotically active progenitors of regenerating neurons. Rod precursors, proliferating cells that normally give rise solely to rod photoreceptors and are the presumed antecedents of the injury-stimulated neuronal progenitors, are not immunostained by antibodies to the pax6 protein. The results of this study document the identity of pax6-expressing cells in the mature retina and demonstrate that in the goldfish pax6 is expressed in neuronal progenitors during both retinal growth and regeneration. © 1996 John Wiley & Sons, Inc.     

Identifying patterns in the diet of mackerel icefish (<Emphasis Type="Italic">Champsocephalus gunnari)</Emphasis> at South Georgia using bootstrapped confidence intervals of a dietary index

Ontogenetic, inter-annual and regional variations in diet were investigated for mackerel icefish, Champsocephalus gunnari, in three successive summer seasons around South Georgia. Stomach contents from 2239 C. gunnari (130–560 mm total length) were examined. A bootstrapping technique was used to calculate confidence intervals for an index of relative importance of prey categories (% IRI_DC). Diet varied significantly between years and age classes but there was little regional difference in diet. In general, diet was dominated by krill, Euphausia superba and by the amphipod Themisto gaudichaudii. Smaller (younger) fish tended to prey on a higher proportion of T. gaudichaudii and small euphausiids such as Thysanoessa sp. and took smaller quantities of E. superba. In a season of poor krill availability (summer of 2003–2004) the proportion of krill in the diet, stomach fullness and fish condition (indicated by length–weight relationships) were significantly lower than in the other summer seasons. A large reduction (>80%) in the estimated annual (2005) biomass of the C. gunnari stock directly followed the season of poor krill availability. This decline was largely because of mortality of 2+ and 3+ fish, which were more krill dependent than 1+ fish. Younger fish appear to have survived, leading to an increase in the estimated population biomass in 2006.     

Temporal shifts in visual pigment absorbance in the retina of Pacific salmon

The visual pigments and photoreceptor types in the retinas of three species of Pacific salmon (coho, chum, and chinook) were examined using microspectrophotometry and histological sections for light microscopy. All three species had four cone visual pigments with maximum absorbance in the UV (_max: 357–382 nm), blue (_max: 431–446 nm), green (_max: 490–553 nm) and red (_max: 548–607 nm) parts of the spectrum, and a rod visual pigment with _max: 504–531 nm. The youngest fish (yolk-sac alevins) did not have blue visual pigment, but only UV pigment in the single cones. Older juveniles (smolts) had predominantly single cones with blue visual pigment. Coho and chinook smolts (>1 year old) switched from a vitamin A₁- to a vitamin A₂-dominated retina during the spring, while the retina of chum smolts and that of the younger alevin-to-parr coho did not. Adult spawners caught during the Fall had vitamin A₂-dominated retinas. The central retina of all species had three types of double cones (large, medium and small). The small double cones were situated toward the ventral retina and had lower red visual pigment _max than that of medium and large double cones, which were found more dorsally. Temperature affected visual pigment _max during smoltification.     

The composition of the coastal fish fauna around Elephant Island (South Shetland Islands, Antarctica)

The composition of the coastal fish fauna around Elephant Island (northern South Shetland Islands) was investigated during seven bottom trawl surveys of FRV “Walther Herwig”, FV “Polarstern” and FRV “Yuzhmorgeologiya” from 1981 to 1998. Low-Antarctic (or lesser or peri-Antarctic) fish species were the predominant element of the coastal fish fauna. Large-scale fishing from 1978 to 1981 reduced stock sizes of the most abundant species Champsocephalus gunnari and Notothenia rossii to the extent that only a small fraction of the initial stock remained. After the period of intensive fishing, Gobionotothen gibberifrons became the most abundant species around the island. The by-catch species, which had probably been less affected by harvesting, recovered by the end of the 1980s/beginning of the 1990s. Fish biomass was highest in the 100- to 400-m depth range. An MDS plot revealed the existence of five groups of species that overlapped in their distribution to some extent. One important factor that separated the five groups was depth. Other factors that might have been important in structuring the vertical distribution of the fish fauna, such as bottom topography and sediment type, could not be investigated. Species composition was dominated by a few abundant low-Antarctic species. In four of the five groups, G. gibberifrons was by far the most abundant species, after C. gunnari and N. rossii had been largely eliminated due to fishing. Only in the 100- to 200-m depth range was C. gunnari more abundant than G. gibberifrons. In the 400- to 500-m depth stratum, a high-Antarctic species, Chionodraco rastrospinosus, and Lepidonotothen squamifrons, a species of Patagonian origin which lacks antifreeze glycopeptides, gained some importance. Species richness showed a positive trend with increasing depth. Evenness and Hill's N1 index were highest in the shallowest and deepest depth strata. Hill's N2 index was lowest in depth strata 3 and 4, which had the most even distribution of the abundant fish species. Accepted: 21 May 2000