A rapid assessment of surveys of egg production of a fishery stock, such as the Japanese anchovies Engraulis japonicus or Japanese sardines Sardinops melanostictus, is one of the information necessary for predicting of the daily catch in the local whitebait fishery. We proposed a sequential combined method that consists the method of Most Probable Number (MPN) and a direct-count in order to reduce the time required to obtain unbiased estimate of the egg densities of the samples. In the method, the mean of egg density is estimated by the MPN if the density is low, but is done by a combination of the MPN and the direct-count if it is high. Effectiveness of the method was evaluated by simulation using the survey data of the Japanese anchovy in Suruga Bay. The results showed that the method provides good estimates of the true mean saving the time. We discussed about the application of this method.

Pond smelt catch in Lake Shinji has been at a low level since 1994. The population has not yet recovered, nevertheless gill-net catch has been banned in spawning season at the river mouth of Hii River, the major spawning ground. We carried out population estimation by the egg production method for fundamental information on further stock management policy. Pond smelt attaches their adhesive eggs to sands or gravels at the bottom. Mean number of pond smelt eggs sampled from 0–6 cm layer of sandy bottom was 88.4 per unit area of 0.05 m² by egg sampling survey in the 2004 spawning season. Total area of major spawning ground in Hii River was 242,987 m². Total number of eggs in 0–6 cm layer of sandy bottom was estimated as 429,601,016. Number of spawning females was calculated as 39,247 individuals, and biomass of both sexes was estimated as 861 kg. Moreover, 2.25 fold eggs were deposited to a depth of 0–15 cm layer compared with 0–6 cm. Spawning population was estimated as 1,937 kg, using the value.

Age, growth, and maturation of elongate ilisha Ilisha elongata were examined in the Seto Inland Sea, Japan, from 2003 to 2005. Standard length (SL) ranged from 250 to 556 mm for adult and immature fish (n=356) and from 52 to 85 mm for juvenile fish (n=33). Almost all of the large-sized fish ≥430 mm SL (97%) were identified as female. The initial maturation sizes of male and female were estimated to be approximately 300 mm and 360 mm, respectively. Seasonal variation in gonadosomatic index and the occurrence of eggs of this species in the same area based on past studies suggest that the spawning period extends from June to August. Clear check marks on sectioned otoliths were formed at the marginal edge once a year between April and October, confirming their annual formation in otoliths. The maximum ages were estimated to be 10 years old in both male and female, but 85% of individuals≥8 years old consisted of females. The von Bertalanffy growth equations based on age–length relationships were estimated, as follows: SLt=422.6 (1-e^{-0.542 (t+0.166)}) for males and SLt=497.1 (1-e^{-0.414 (t+0.225)})) for females, where SLt is the SL (mm) at t (year). These two equations were significantly different (p<0.01), indicating that females become larger than males.