Neuroendocrine mechanisms in relation to control of maturation in cultivable teleost fishes

Reproductive processes are by no means fully impaired in captivity. The progressive development of the gonads -remains, in general, inhibited upto the final stages of gamete maturation, and it is only at the point of gamete release that the sequence is arrested. Both-gonadal maturation and spawning behaviour have long been known in responses to environmental stimuli viz., temperature, light and rainfall etc

Neurological endocrinology: the coordinating mechanism

The nervous and endocrine systems are integrative in nature for they provide th'e organism with sophisticated external and internal sensing devices which feed information into the central nervous system for appropriate responses of the target system

Freezing of viable embryos and larvae of marine shrimp, Penaeus semisulcatus de Haan

Although sperm cryopreservation has been carried out successfully in a number of commercially important aquatic species, particularly in some teleost fish (see review of Rana in Muir & Roberts 1993) and also shellfish (Subramoniam 1993), the technology is still not at the stage of advanced commercial application that is seen in domestic mammals. Cryopreservation of eggs and embryos, of aquatic animals however, is a virgin field in cryobiology and has not yet received any appreciable amount of attention. The first successful attempt at the cryopreservation of embryos of sea urchin was reported by Asahina & Takahashi (1978). Later Zell (1978) and Erdahl & Graham (1980) have reported preliminary attempts to freeze the eggs of rainbow trout

Fisheries research and development in India

The fisheries sector of India is immensely contributing to the economy of the country. It provides valuable fore ign exchange and employment to millions of people. At the same time it is an instrument of livelihood for a large section of economically backward population of the country

Physiological and Endocrinological approaches in captive breeding of marine finfish

Reproductive processes are by no means fully impaired in captivity. The gradual and progressive development of the gonads remains, in general, uninhibited upto the final stage of gamete maturation, and it is only at the point of gamete release that the sequence is arrested. Both gonadal maturation and breeding behaviour have long been known in responses to environmental stimuli viz., temperature, light, rainfall etc. Our fishery scientists have made a timely breakthrough by inventing the technique of induced breeding through hormonal manipulation. Though the induced breeding technique has now been successfully used for carps many brackishwater and marine fishes have either responded to this technique with partial success or no response. This is because of the lack of understanding the mechanisms involved in the environmental complexities and their impact on neuroendocrine mechanisms in control of reproduction

A novel magnetic resonance imaging postprocessing technique for the assessment of intervertebral disc degeneration-Correlation with histological grading in a rabbit disc degeneration model.

Introduction:Estimation of intervertebral disc degeneration on magnetic resonance imaging (MRI) is challenging. Qualitative schemes used in clinical practice correlate poorly with pain and quantitative techniques have not entered widespread clinical use. Methods:As part of a prior study, 25 New Zealand white rabbits underwent annular puncture to induce disc degeneration in 50 noncontiguous lumbar discs. At 16 weeks, the animals underwent multi-echo T2 MRI scanning and were euthanized. The discs were stained and examined histologically. Quantitative T2 relaxation maps were prepared using the nonlinear least squares method. Decay Variance maps were created using a novel technique of aggregating the deviation in the intensity of each echo signal from the expected intensity based on the previous rate of decay. Results:Decay Variance maps showed a clear and well demarcated nucleus pulposus with a consistent rate of decay (low Decay Variance) in healthy discs that showed progressively more variable decay (higher Decay Variance) with increasing degeneration. Decay Variance maps required significantly less time to generate (1.0 ± 0.0 second) compared with traditional T2 relaxometry maps (5 (±0.9) to 1788.9 (±116) seconds). Histology scores correlated strongly with Decay Variance scores (r = 0.82, P < .01) and weakly with T2 signal intensity (r = 0.32, P < .01) and quantitative T2 relaxometry (r = 0.39, P < .01). Decay Variance had superior sensitivity and specificity for the detection of degenerate discs when compared to T2 signal intensity or Quantitative T2 mapping. Conclusion:Our results show that using a multi-echo T2 MRI sequence, Decay Variance can quantitatively assess disc degeneration more accurately and with less image-processing time than quantitative T2 relaxometry in a rabbit disc puncture model. The technique is a viable candidate for quantitative assessment of disc degeneration on MRI scans. Further validation on human subjects is needed

Physiology of digestion in fishes and shellfishes

Some fish feed on plants, some on animals and a third group derives ijs protein, carbohydrate, fats, vijamins and minerals from both plant and animal sources. Some fishes live on blood and tissue fluid of other fishes (eg. Petromyzon). Some fishes feed on plankton during part of their life and some throughou1 life. Others feed on weeds. Many other feed on zooplankton and also on other larger animals like annelid worms, snail. mussel, clams, crustaceans, insect, birds, mammals, reptiles and amphibians. Even human beings are found in the stomach

Neuroendocrine regulation of ovarian maturation in the Indian white prawn Penaeus indicus H. Milne Edwards

Neuroendocrine Regulation of ovarian maturation in the Indian white prawn Penaeus indicus H. Milne Edwards. Aquaculture, 98: 381-393. The control and regulation of ovarian maturation by neurosecretory elements in the eyestalk, brain and thoracic ganglia of Penaeus indicus have been examined. In the X-organ complex of the eyestalk, secretions from type A and B cells are apparently involved in inhibiting ovarian maturation, while in the brain and thoracic ganglia, secretions from type GN, A and B ce!ls had a stimulatory effect on the ovary. The pyriform C cells were not involved with ovarian maturation. Both unilateral and bilateral eyestalk ablation resulted in precocious maturation of the ovary. The histology of the remaining eyestalk in unilaterally ablated animals revealed that all the NSCs in the X-organs were in a suppressed state and the sinus gland was devoid of granular aggregations. Abnormal behaviour was noticed in bilaterally ablated prawns and strangely few animals moulted with developing ovaries. Due to the synchronous occurrence of moulting and reproductive activities the probability of both gonad and moult inhibiting hormones being the same is discussed. In addition the relationship between gonadal maturation and the moult cycle has also been studied

Effect of androgenic gland ablation on sexual characters of the male Indian white prawn Penaeus indicus H. Milne Edwards.

Bilateral and rectomy was carried out in penaeid prawns.Results indicated that in the absence of androgenic glallds male secondary sexual characters once lost cannot be regenerated. Andrectomy also appeared to block spermatogonial differentiation