Journal of Endocrinology and Reproduction

S. K. Maitra ¹, M. Seth ¹, A. Chattoraj ¹

Affiliations
1 Department of Zoology, Visva-Bharati University, Santiniketan – 731 235, IN

Abstract

Annual variation in photoperiod is the most regular phenomenon that has strong predictive value in the temporal organization of seasonal activities in biological world, especially reproduction. Carefully controlled studies demonstrated importance of photoperiods in the regulation of annual reproductive events in diverse groups of animals including fish. Apart from academic interests, study in fish has gained momentum because of its tremendous economic importance as food. Thus, for obvious reasons, efforts are continued to develop technologies for increasing fecundity and growth of fish in culture. As a result, photoperiodic manipulation has emerged as an effective tool of reproductive management in culture fisheries, and understanding the physiology of photoperiodic regulation of fish reproduction became the priority topic of research in different countries. The present paper reviews and summarizes the information gathered in recent years on the importance of photoperiod and the mechanism of photoperiodic signal transduction in the photo-neuroendocrine system in fish emphasizing the role of pineal organ, which is considered as an intermediary between the environment and the endocrine system in vertebrates.

Keywords

Fish, Pineal Organ, Photoperiod, Photoreceptors, Reproduction.

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S. K. Maitra ¹, R. Dey ¹, S. Bhattacharya ²

Affiliations
1 Department of Zoology, Visva-Bharati University, Santiniketan-731 235, IN
2 Department of Zoology, University of Burdwan, Burdwan-713 104, IN

Abstract

Reproduction in most fishes is discontinuous or seasonal. Rhythms with a periodicity of one year represent major components in the adaptation of concerned fish to their environment. Environmental factors, such as light and temperature, play an important role in the synchronization of this rhythmic activity of reproduction. In vertebrates, synchronization is mediated through the system which is composed of sensors and circadian oscillators like the pineal organ, the lateral eyes and the suprachiasmatic nuclei of the hypothalamus. The fish pineal seems to be involved in the timing and control of reproduction. On the basis of several experimental evidences, it is believed that the pineal is able to translate environmental information (photoperiod, temperature) into rhythmic messages. To date, two kinds of signals have been clearly identified, a nervous signal and a neurohormonal signal, i.e., melatonin. Whereas the functional significance of the nervous signal is not yet clearly understood, there is increasing evidence that in at least temperate zone vertebrates, melatonin is the chemical messenger of photoperiod (Zeitgeber). In contrast to the neuronal message, elaborated mainly (if not exclusively) by the pineal of ectotherms, melatonin appears to be a conservative signal in the vertebrate phylum. In all the species investigated so far, melatonin production is high during nighttime and low during daytime. Despite this apparent homogeneity, the involvement of the pineal in the temporal organization of reproduction, as well as the mechanisms by which the photic information is processed in the control of gonadal germ maturation in fish have been the matter of great interest. Molecular mechanism involved in photoreceptor-induced pathway in fish is yet to be known, without which benefit from such information remains unveiled.

Keywords

Fish, Light, Pineal, Reproduction.

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B. Sharmistha ¹, C. Asamanja ¹, S. K. Maitra ¹

Affiliations
1 Department of Zoology, Visva-Bharati University, Santiniketan - 731 235, IN

Abstract

The present communication deals with the ultrastructurai and morphometric study of the pineal complex in a hitherto unstudied Indian major carp Catia catla. In this fresh water teleost, the pineal complex is a discrete structure composed of a distal 'end vesicle' (EV), a long connecting 'pineal stalk' (PS), and a convoluted 'dorsal sac' (DS). Light microscopic study demonstrated that the parenchyma of the EV contains two types of cells, viz., 'light cells', and 'dark cells'; of which only 'light cells' exhibit significant annual cyclic variations in the nuclear diameter. Consequently, attempts have been made to employ transmission electron microscopy for identification and characterization of the photosensory cellular components of the pineal complex in the carps following exposure to continuous illumination (LL; 24L) or continuous darkness (DD : 24D) for 30 days during the different phases of an annual reproductive cycle. The study also indicated the presence of two types of cells which shared the features of photoreceptorand supporting cells in the EV of the pineal complex respectively. Significant changes were noted in the size and shape of various sub-cellular organelles in the photoreceptor-, but not in the supporting cells of the pineal EV following exposure to LL or DD schedules. While an increase in the nuclear diameter was noted in the photoreceptor cells of EV in the carp held under DD in each part of the annual gonadal cycle, significant regressive changes occurred in the photoreceptor cells of the EV in LL group offish but only during the preparatory and the pre-spawning phases of theannual cycle. Commonly, it was found that an increase in the number of secretory granules, synaptic vesicles and synaptic ribbons, and hypertrophy of mitochondria occurred in the pinealocytes of carps held under DD, while regressive changes in the parenchymal cells of EV resulted in the pineal complex following exposure to LL. It was interesting to note that morphometric and uitrastructurai changes in response to altered lighting conditions were demonstrable only in the EV, but not in the PS and DS of the pineal complex. Thus, it appeared conclusive that the pineal complex in Catla catla is directly associated with photoreception, and the EV is the only part of pineal complex that performs the alleged function. However, the etiology of differential responsiveness of the EV photoreceptor cells to LL in different parts of annual reproductive functions remains unknown.

Keywords

Carp, Catla Catla, Light, Darkness, Pineal Complex, Ultrastructure.

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S. Anamika ¹, S. K. Maitra ²

Affiliations
1 Gupta College of Technological Sciences, Asansol-713301, IN
2 Department of Zoology, Visva-Bharati University, Santiniketan-731235, IN

Abstract

The present study aimed at elucidation of the relative role of the retina and the pineal organ in the photoperiodic regulation of seasonal events of initiation and termination of gametogenic and steroidogenic activities of the testis in roseringed parakeet Psittacula krameri. Accordingly, the birds were either pinealectomised surgically, or chemically induced for blindness, or subjected to both the treatments simultaneously during the months of November and February corresponding to the late progressive and breeding phases of the annual gonadal cycle, respectively.

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