An investigation of batch-spawning reproduction in captive yellowtail flounder, Pleuronectes ferrugineus

The batch-spawning reproduction of female yellowtail flounder, Pleuronectes ferrugineus, was examined in a captive setting over the spawning periods of 1994 and 1995. Individual female yellowtail were examined daily with the objectives of determining the inter-ovulatory period of this species, as well as, the annual egg production, mean batch fecundity and number of batches per female. Egg quality measures (fertilization and hatching rates) were also made on batches from females to quantify maternal differences and inter-batch variation within females in egg survival rates. -- A one-day inter-ovulatory period was predominant in this species and the frequency of this period increased in 1995 due to reductions in irregular ovulatory activity detected in certain females in 1994. The mean duration of spawning for individual females ranged between 31 to 48 days, over which time egg diameter and dry weight were observed to decrease within individual females. -- Female yellowtail flounder demonstrated considerable individual variation in seasonal egg production. In 1994, the mean female production was 550,000 eggs (7.9 x 10⁵ eggs kg⁻¹ spawning female), in 1995 this increased to 1,187,000 eggs (1.5 x 10⁶ eggs kg⁻¹ spawning female). The number of ovulations per female was high, a mean batch number of 14 was seen in 1994, rising to 22 in 1995. Small batch sizes (