ISSN:0006-8977    

DOI:10.1159/000116484

出版商:S. Karger AG    

年代:1989

数据来源: Karger

ISSN:0006-8977    

DOI:10.1159/000116485

出版商:S. Karger AG    

年代:1989

数据来源: Karger

摘要:

Overviews of critical period concepts, as they appear at several biological levels, are presented. In embryology, critical periods generally refer to restricted periods in development during which undifferentiated groups of cells can be induced to differentiate. In neurobiology, critical periods are those during which neural circuits are particularly plastic and subject to molding by cellular processes and by experience. The ethological critical period concept advances the idea that an individual's behavioral characteristics can be more strongly influenced by a given event (some stimulus) at one stage of development than at others. For example, this is the period during which young birds imprint upon their parent(s) and learn their species' songs, or during which young salmon imprint to the odor of their home streams. The fisheries science critical period, an ecological concept, refers to a restricted time in the early life history of fish during which there is massive mortality. For many fish, this event is generally considered the primary factor controlling the size of the adult population. The cause of variable mortality between years is thought to be a result of differential food availability and predation during a critical stage in early fish larval development. At each biological level of the critical period, spatial and temporal overlap between the developing organism and specific environmental input is essential. It is likely that critical periods in embryology, neurobiology and ethology are causally interrelated in a hierarchical manner and that they can be manifested as ecological critical periods. For example, if the abundance of food for fish larvae is low for the duration of a sensitive period in neural development, the appropriate neural network underlying foraging behaviors may not develop optimally even if food abundance subsequently increases. These fish will die, producing, in this case by definition, an ecological critical period.

ISSN:0006-8977    

DOI:10.1159/000116486

出版商:S. Karger AG    

年代:1989

数据来源: Karger

摘要:

Unlike the case in birds and mammals where addition of neurons and muscle fibers is almost exclusively an embryonic process, fish form new sensory receptors, central neurons and muscle fibers postnatally. We have investigated the development of the sonic neuromuscular system, consisting of a spinal sonic motor nucleus (SMN) and a pair of sonic muscles intrinsic to the swimbladder, in the oyster toadfish Opsanus tau. The SMN differentiates late in embryonic development, and neurons increase in number and size through the larval period and for 7–8 years of adult life. Neuron number increases from a median of 35 to 322 cells, from the time of differentiation through the larval period, and to almost 3,000 cells in large fish. Immature neurons appear to originate from precursor cells in the base of the ventricular zone ofthe central canal and are added throughout the SMN. No evidence of cell death was seen. The number and diameter of sonic muscle fibers increase for life (about 16- and 3-fold, respectively); fiber number ranges from almost 31,000 in a 1-year-old juvenile to almost 500,000 in large animals. Fiber splitting provides a possible mode of fiber addition. Multiyear addition of neurons and muscle fibers indicates that embryonic processes continue beyond the termination of larval life.

ISSN:0006-8977    

DOI:10.1159/000116487

出版商:S. Karger AG    

年代:1989

数据来源: Karger

摘要:

The superorder Elopomorpha (orders Anguilliformes, Elopiformes and Notacanthiformes) is characterized by the presence of a unique larval stage termed the leptocephalus. The basic morphology, chemical composition, developmental pattern, and behavior of premetamorphic and metamorphic leptocephali are reviewed. The eyes, olfactory organs and pores of the lateral-line system are well developed, suggesting that these sensory structures play an important role in larval behavior. Premetamorphic larvae are pelagic and in some elopomorphs subsequent development is associated with migration to coastal waters where metamorphosis takes place. The factors controlling onshore migration, as well as the metamorphic trigger(s), are unknown. The possible relationships between sensory systems and behavioral changes during the different phases of larval development are presented.

ISSN:0006-8977    

DOI:10.1159/000116488

出版商:S. Karger AG    

年代:1989

数据来源: Karger

摘要:

The present study deals with aspects of the brain development in the roach, Rutilus rutilus, a common mid-European cyprinid fish. The morphogenesis of selected brain areas from hatching to early juveniles was examined on serial paraffin cross-sections. From early juveniles to large adults, brain growth was quantitatively analyzed by computer-aided planimetry. The hatchlings of roach show a cytologically distinct optic tectum, but a poorly differentiated brainstem, reflecting the predominance of the optic sense during the larval planktivorous period. The differentiation and outgrowth of chemosensory brainstem centers is related to the onset and development of benthivorous feeding in juveniles. The optic tectum decreases in size relative to the total brain volume from juveniles through adults. The corpus cerebelli increases in relative size, whereas chemosensory and acousticolateral centers grow isometrically with the brain as a whole.

ISSN:0006-8977    

DOI:10.1159/000116489

出版商:S. Karger AG    

年代:1989

数据来源: Karger

摘要:

The ampullary electroreceptor organs of the teleost fish Clarias gariepinus converge to single afferent neurons. During the first 4 months of ontogeny the convergence ratio (CR) increases from 1 to 3. Extracellular single-unit recordings show that a 3-fold increase in CR results on average in a 3.6-fold increase in sensitivity measured at stimulus frequencies of 2, 8 and 20 Hz, and in a small but significant 1.1-fold increase in resting discharge. Adaptation of the primary afferents could account for the differences between changes in sensitivity and resting discharge.

ISSN:0006-8977    

DOI:10.1159/000116490

出版商:S. Karger AG    

年代:1989

数据来源: Karger

摘要:

The post-embryonic development of the neural retina and the pigment epithelium of the rainbow trout was analysed by electron microscopy. Particular attention was paid to the period when these fish change from photonegative to photopositive behaviour. In photoreceptors, light-sensitive outer segments arise prior to synapses. Subsequent rapid synaptogenesis in the inner plexiform layer results in the establishment of the pathway between photoreceptors and ganglion cells. Interreceptor contacts and feedback synapses, associated with the integration of colour and spatial information, appear when the fish become photopositive, swim to the water surface and begin exogenous feeding. Retinal development parallels that of higher optic centres and visual acuity, as reported by other authors.

ISSN:0006-8977    

DOI:10.1159/000116491

出版商:S. Karger AG    

年代:1989

数据来源: Karger

摘要:

The post-embryonic development of the neural retina and the pigment epithelium of the rainbow trout was analysed by electron microscopy. Particular attention was paid to the period when these fish change from photonegative to photopositive behaviour. In photoreceptors, light-sensitive outer segments arise prior to synapses. Subsequent rapid synaptogenesis in the inner plexiform layer results in the establishment of the pathway between photoreceptors and ganglion cells. Interreceptor contacts and feedback synapses, associated with the integration of colour and spatial information, appear when the fish become photopositive, swim to the water surface and begin exogenous feeding. Retinal development parallels that of higher optic centres and visual acuity, as reported by other authors.

ISSN:0006-8977    

DOI:10.1159/000316068

出版商:S. Karger AG    

年代:1989

数据来源: Karger

摘要:

Histological analyses of the retina of Salmo trutta post-embryos exhibit rhythmic disc shedding at 6 weeks, followed by cyclic retinomotor movements at 7 weeks. Diurnal variations in cAMP concentration, as established by a radioreceptor assay, develop simultaneously with retinomotor movements and are fully expressed at 9.5 weeks. In continuous darkness, neither retinomotor movements nor intra-ocular peaks of cAMP occur, indicating that the endogenous oscillator for retinomotor movements and cAMP levels is not yet developed.

ISSN:0006-8977    

DOI:10.1159/000116492

出版商:S. Karger AG    

年代:1989

数据来源: Karger