Estimation of Important Reproductive Parameters for Management of the Shoemaker Spinefoot Rabbitfish (Siganus sutor) in Southern Kenya

Abstract

The shoemaker spinefoot, Siganus sutor, is a member of the family Siganidae, commonly known as rabbitfish. Many demersal fish populations in the Kenyan waters are heavily exploited, and fishing effort may be above optimum levels for some species. This study was aimed at determining missing parameters on spawning periodicity and maturity of S. sutor for the Kenyan south coast area of Msambweni, complementing a suite of parallel studies on spawning aggregation based fisheries for this species. A total of 376 samples were collected over 12 months, including 85 that were collected over four lunar phases in November and December 2010. Monthly GSI showed two distinct peaks, one in June and July and one in November and January, suggested two distinct spawning periods within the year. The highest GSI was recorded in November while the lowest values occurred in April August and September. A lunar pattern in ovarian development stage was seen with the highest proportion of ripe ovaries (RI) observed in the full moon phase, whereas running ripe (RR) or hydrated ovaries dominated samples in the last quarter. Imminent spawning was confirmed by the presence of hydrated oocytes and post ovulatory follicles, observed primarily during the last quarter and to a lesser extent during full moon. GSI value Kruskal-Wallis test showed significant differences in GSI between moon phases (p< 0.05). In conclusion, histological analysis of ovaries points to synchronous development of oocytes with moon phases, suggest that their release takes place over short period of time after the full moon.