Spawning periodicity, fecundity and egg size in laboratory-held stocks of a substrate-spawning tilapiine, Tilapia zillii (Gervais).

摘要

Spawning traits were recorded for a strain of redbelly tilapia (Tilapia zilli) (n = 101) from the Tilapia Reference Collection at Stirling University. Female broodfish were placed into individually partitioned glass aquaria (up to 20 per tank) for at least 80 days. 66% of females spawned once and 31% spawned more than once. Inter-spawning-interval (ISI) averaged 26 days and the mean number of days elapsed per spawn (based upon both spawning and non-spawning fish amongst the females studied) averaged 61 days and was considered the best estimate of spawning periodicity. The shortest spawning cycle observed was 7 days. There was no relationship between ISI and fecundity. Fecundity increased with increasing maternal size (log scale, r2 = 0.48, P<0.001) and ranged from 461 to 11 640 eggs/clutch (mean = 3606±280). Egg size varied within a relatively narrow range. Variations in egg size did not, generally, relate to maternal size; mean egg diameter was 1.5 mm. Regression analysis revealed strong and significant relationships between fish size (total length and body weight) and relative fecundity and total egg volume (P<0.001). Relationships between fish size and various indices of egg size (mean egg diameter, mean egg dry weight and mean egg volume) were far weaker (r2 = 0.02-0.10).