Abstract

The present investigation was carried out to study the reproductive biology of the Oncoryhncus mykiss at Laribal hatchery, Dachigam National park, Srinagar, Jammu and Kashmir from February 2018 to March 2019. The study was carried out to identify and illustrate developmental stages of oocytes of female rainbow trout and correlate them with seasonal maturity, organo-somatic indices and with change in biochemical composition. During the present study ovary samples were taken and processed for routine histological analysis. Morphological and anatomical changes in ovaries were recorded. Different oocytes were observed in ovaries at different developmental stages. The entire reproductive phase was divided into four major divisions: - Immature phase, developing phase, spawning phase and post- spawning phase. The six different types of oocytes that were identified in this study include chromatinnucleolus oocyte, peri-nucleolus oocyte, cortical alveolus oocyte, yolk vesicle oocyte, yolk granular oocyte, and mature oocyte. The maximum level of gonadosomatic index (12.33 ± 1.04%) and reduced value of hepatosomatic index (0.82 ± 0.08%) was seen in January which signifies that December to February is the peak spawning period of rainbow trout. It was also observed that June to August is growth phase, September to November is maturation phase, and March to May is the post-spawning phase of rainbow trout. Ninety eight captive bred female rainbow trout tissues were investigated for their biochemical composition to establish their need of formulating nutrient-rich broodstock diets. The biochemical investigation of muscle, liver and ovary of captive bred female rainbow trout from Laribal hatchery, Dachigam, J&K showed that the maximum amount of moisture content (75.30%) was found both in ovaries of immature females and in muscles of spawning female (75.20%) while as significantly lowest amount of moisture was found in liver of spawning females (71.10%). The crude protein content among four phases in female rainbow trout was significantly (p < 0.05) higher (23.00%) in muscles of immature females while lowest (13.50%) in liver of spawning females. The post-hoc test revealed that the crude protein content in liver and ovary of developing females (14.00%; 14.30%) varied insignificantly. Similarly, the highest amount of lipid was recorded in liver of both developing and spawning females (9.90%; 9.12%) which was significantly (p < 0.05) higher compared to all other phases. Significantly lowest amount of lipid content (1.79%) was noticed in muscles of developing females with intermediate amount of lipid content (3.60%) in muscles of immature females. The inverse relationship between moisture and lipid was also found. It was observed that during different gonadal stages of female rainbow trout, the ovaries get its protein and lipid from other tissues mostly from liver. Therefore, it is necessary to incorporate highly assimilated feed with high protein and lipid content. The muscle of immature females thus belongs to high protein and low-fat category and can be subjugated commercially for human consumption. Hence, it was concluded that the identification and classification of various oocytes, estimation of organo-somatic indices as well as fluctuations in biochemical composition of different tissues are enormously significant in understanding the gonadal changes during different seasons of a year and thus present study is of utmost significance for preservation and management of the species studied.

Keywords: Biochemical; Protein; Lipid; Muscle; Liver; Trout; Gonads