BACKGROUND: Maturity of silver carp (Hypophthalmichthys molitrix) ovary takes place at 2-8 years old and it is depends on photoperiod and environmental water temperature. Objectives: The aim of this study was to identify  macroscopical and microscopical structure of silver carp  ovary in  two categories of  body weight, total body length and  at  2 and 4 years old  in Khuzestan province climatic conditions. Methods: 20 silver carp ovaries were studied in two groups: Group 1(G1): 10 fish with total body length 46 ±1.33 Cm and weight 1050±0.09 grand approximately 2 years old. Group 2(G1): 10 fish with total body length 86±3.64 Cm and weight 5460±800 gr and approximately 4 years old. For the histometrical studies, 5-6 µ sections were made by routine paraffin embedding method and stained by H&amp;E and PAS. Results: Microscopic results showed that ovaries of G1 covered by a thin loose connective capsule which numerous of egg-bearingtrabecula extended from capsule into ovaries. These trabecula contained primary germ cells, oogonium, chromatin nocleolus, perinocleolus and cortical alveolus follicles. Ovaries of G1 do not have yolk and mature follicles. But in ovaries of G2, growth and mature follicles were observed and mature follicles were most follicles. Histometrical results showed that there are not a significant differences in diameter of follicles, oocytes and oocytes nucleolus in G1 and 2. The maximum and minimum diameter of follicles were seen in mature and chromatin nucleolus follicles respectively. The Zona plucida thickness was increased from corticalalveolus (1.53±1.11 mm) to mature follicles (6.88±0.21 mm) significantly (p<0.05). ConclusionS: The most interesting finding of this study is that in Khuzestan Province climate, the ovary of silver carp fish in G1, with average weight 1050 ±0.09 gr and total length 46±1.33 Cm and approximately of 2 years old is immature but ovary of G2 with average weight of 5460± 800 gr and total length 86±3.64 Cm and approximately 4 years old is mature.

Objectives: Avian lymphatic system plays a very significant role in immunity as well as disease control. This research aimed to investigate the histomorphological changes and involution of the thymus of Sonali chicken at different post-natal stages in Bangladesh as the age-related changes of the thymus of Sonali chicken were not described before. Materials and methods: A gross and microscopic investigation was performed on the thymus of 25 healthy Sonali chickens representing different stages of post-natal life: days 1, 14, 28, 42, and 56. Experimental chickens were sacrificed by cervical subluxation, and the thymus was collected and subjected for both the gross and histological studies. The histological changes were examined with light microscopy after H&E staining. Results: The thymus was located in close association of the jugular vein, having a long chain of thy¬mic lobes, 58 lobes on each side. The statistically significant age-related changes were observed (p &lt; 0.05). All gross parameters (weight, length, width, and thickness) found to be increased up to day 42. On day 56, the growth was found to decline from the previous groups. The microscopic observations revealed the same pattern of changes such as gross parameters, i.e., continuously increased till day 42 and then declined (p &lt; 0.05). At day 56, the involutory signs such as partial loss of interlobular septa and accumulation of adipose tissue in connective tissue septa were found. Conclusion: It is well known that in chicken, after a certain period, the thymus got involuted. In Sonali chicken of Bangladesh, the age of involution was notified at day 56/8th week of the post-natal stage, which was correlated both in macro- and microscopic observations. [J Adv Vet Anim Res 2020; 7(2.000): 324-330]