Effectiveness of Using a Vinyl Sheet to Reduce Mortality Caused by Collision During Rearing of Pacific Saury Cololabis saira

To reduce mass mortality of Pacific saury caused by collision with the tank wall, we examined rearing of saury in a tank with a vinyl sheet attached to the tank wall, and no vinyl sheet tank. We compared survival rate and ratio of the lower jaw length to the knob length of those fish. Survival rate of the former was higher than the latter. No significant difference was recognized for the ratio. These results suggest that the vinyl sheet could not reduce the damage to the lower jaw, but it could reduce the mortality caused by collision

Relationships Between Survival Period and Temperature of Newly Hatched Pacific saury Cololabis saira under Starvation Conditions

To clarify the relationships between the survival period of newly hatched Pacific saury Cololabis saira which use only endogenous nutrition and water temperature, we observed the survival periods under starvation conditions at four temperatures (10, 15, 20 and 25°C). The starvation tolerance period was shortened with increasing temperature. This study suggests that newly hatched Pacific saury can survive for approximately 5-10 days (50% mortality period) without feeding in 10-25°C under non-predator conditions, but such an extended period of starvation is considered to affect subsequent growth and survival

Validation of otolith daily increments for larval and juvenile Japanese halfbeak Hyporhamphus sajori

Daily ring formation was verified by examining the growth of the marginal increment on sagittal otoliths of larval and juvenile Japanese halfbeak Hyporhamphus sajori. The relationship between age (x) and number of increments (y) is y = 1.0x + 2.0. The first daily increment was formed during the 2 days before hatching. The relationship between the number of rings deposited after the alizarin complexone (ALC) mark (x) and the number of increments (y) is given by: y = 1.0x − 0.2. The index of completion of the marginal increment was 99 ± 4.1% (mean ± S.D.) at 04:00, and from 24 ± 4.4% at 08:00 it increased with time of day and reached 98 ± 3.6% until the next day at 04:00. Growth of the incremental zone started a few hours after sunrise prior to which the discontinuous zone seemed to be formed. Light rhythms tend to be one of the most important factors for the formation of the marginal increment on otoliths. Based on the relationships between time of day and the marginal increment on otoliths, it would be possible to estimate the predation time for specimens retrieved from stomach contents, and also clearer analysis of the growth history immediately prior to the sampling time

Growth and maturation of Pacific saury Cololabis saira under laboratory conditions

This study details the growth and maturation processes of Pacific saury Cololabis saira from eggs to first spawning under laboratory conditions. They were reared at 20°C, and fed almost to satiation every day. There was no significant difference in the knob length (KnL) between males and females, and so data for both sexes were combined in the following Gompertz growth formula: KnL t = 277.1 exp[−exp(−0.015 (t − 83.8))]. The first spawning was observed 243 days after hatching (DAH). At the beginning of spawning, when the mean KnL was about 250 mm, only several hundred eggs were spawned at most. The spawning continued, and the number of spawned eggs increased notably after 260 DAH. Correlation and stepwise multiple regression analysis of the gonad somatic index (GSI) of Pacific saury versus KnL, CF, and DAH revealed that only DAH (R = 0.88 and 0.72 for males and females, respectively) was significantly correlated with GSI of Pacific saury (P < 0.001). This result suggests that DAH is one of the most influential factors for maturation in this species