Subchronic effects of neem Azadirachta indica A. Juss. seed extract on female reproductive system of tilapia Oreochromis niloticus Linn. / Jirarach Srijunngam = ผลกึ่งเรื้อรังของสารสกัดเมล็ดสะเดาอินเดีย Azadirachta indica A. Juss. ต่อระบบสืบพันธุ์เพศเมียของปลานิล Oreochromis niloticus Linn.
Biopesticides deriving from neem, Azadirachta indica A. Juss.,have been widely used in various agricultural areas in Thailand. Neem products have been reported to have antifertility properties in insects and mammals. Due to its wide-range in mode of action on many target and non-target species, the adverse effects on reproductive system of economic fish species were considered. Objective of this study was to investigate subchronic effects of Neemix, a neem seed extract on female reproductive system of Nile tilapia Oreochromis niloticus Linn. Nile tilapias at the age of 1 month were kept in a static renewal system throughout the study. The acute static toxicity bioassay was carried out to determine the LC50 of the extract after 96 hours. It was determined at 36.25 mg/l and from this value, a sublethal concentration of subchronic toxicity test was calculated at 25.07 mg/l. The tilapias were treated with this concentration for 7 months. The female were randomly selected (n = 20) in every month from the 4th to 7th month of the experiment. The fish were sacrificed, ovaries were weighted, fixedand taken for oocyte counting and for conventional histological method. The oocytes in ovary of the tilapia were classified into 3 size groups and 5 stages of development including the small size, chromatin nucleolar stage and perinucleolar stage; the medium size, yolk vesicle (cortical alveolar) stage and vitellogenic stage; and the large size, ripe stage. Postovulatory follicle, corpora lutea was also detected after the 5th month. Effects on fecundity were indicated by the lower GSI and oocyte number in the treated fish from every months of experiment. Significant difference (p<0.05) of GSI was detected on the 6th month. The total number of oocytes in the ovary of the treated fish were significantly different (p<0.05) from the controls on the 4th and 7th month. Reproductive failure in the fish exposed to the neem seed extract was obviously seen when the number of ripe oocyte were compared. There were significant differences (p<0.05) in all experimental period. Histological changes in ovarian tissue of the treated fish were observed including the decrease in number of mature oocyte, yolk deposition both intraoocytic and extraoocytic area and adipose tissues. Histopathological events observed on oocyte in ovary of the treated fish were hyperbasophilic of the oocyte with shrunken cytoplasmic borders and degeneration of follicular cells in the chromatin nucleolar, perinucleolar stage and yolk vesicle stage. Oocytes in all stages of the treated fish were seen abnormal in shape. Large, empty interfollicular spaces were presented and inflammation in interstitial tissues and ovarian capasule were also noted as histopathological lesions. These events indicate that the disturbance in the process of ovarian development and spawning of the neem treated fish is occurred.