Reproductive maturation and induced breeding of two geographical groups of grey mullet, Mugil cephalus Linnaeus, 1758

Success in captive reproduction and hatchery-based seed production is fundamental for the development of sustainable aquaculture of grey mullet in India. In the present study, the induced breeding and reproductive performance of two geographically different groups of grey mullet, Mugil cephalus sourced from east and west coasts of India were studied under captivity. Grey mullets sourced from east coast, Chennai, India (EP-E: eastern mullet population in situ; 782.4 +/- 58.26 g) and west coast, Ernakulam, India (WP-E: western mullet population transferred to eastern location; 726.1 +/- 31.09 g) were reared under uniform captive conditions at Muttukadu Experimental Station, ICAR-CIBA, Chennai. On the east coast, captive maturation and reproductive performance were studied for two years from October 2015 - January 2018 (EP-E and WP-E; N = 140). To accelerate reproductive maturation, female mullets were treated with intramuscular cholesterol pellets of gonadotropin-releasing hormone (GnRHa, 200 mu g/fish) and males with silastic implants of 17-alpha-methyl testosterone (5 mg/fish). On the west coast, grey mullets (WP-W: western mullet population in situ; N = 130) were reared in earthen ponds under similar experimental conditions as EP-E and WP-E. Fourteen induced breeding trials were carried out in eastern population whereas 24 induced breeding trials were carried out in the western population. The percentages of mature fish initially and at 12 and 24 months for EP-E were 48.7, 57.5, and 50% whereas for WP-E, they were 0, 2.4, and 14.7% respectively. The maximum average oocyte diameter recorded for EP-E was 538 +/- 6 mu m and that for WP-E was 564 +/- 21 mu m. The peak reproductive periods of captive grey mullet on the east coast were November (EP-E) and December - January (WP-E). Induced breeding trials using EP-E were successful using females with an average oocyte size in the range of 520-535 mu m from 6th - 20th November and the fertilisation rates ranged from 1 to 35%. The peak reproductive period of WP-W extended from June to August and successful induced breeding trials were conducted using females with average oocyte size of 540-570 mu m, from 15th June - 20th July. The fertilisation percentage varied from 45 to 85%. Western mullet population exhibited reproductive dysfunctions when maintained under captivity on the east coast. The reproductive periods of captive grey mullets on the east and west coasts of India are asynchronous and provide the opportunity for two nonoverlapping breeding periods for captive reproduction of grey mullets in the region.