EFFECT OF SALINITY CHANGE AND EXPOSURE TIME ON THE EGG STAGES OF TWO ABALONE SPECIES Haliotis discus discus AND Haliotis gigantea

Torrential rainfall is one of the main external cause that affects coastal marine species during spawning seasons.  Heavy rain over a certain period may have effects on embryonic development of coastal marine organisms. The Japanese government started a marine stock enhancement programme in 1963 and abalone was one of the first targets to help restore the decrease in wild stock population. Even though the Japanese large-scale stock enhancement programme was expected to sustain the fishery production of abalone, it was claimed that stocking cultured juveniles had not contributed to the enhancement of wild abalone stocks. Therefore, the objective of this study is to find out the combined effects that salinity change, and exposure time have on disk abalone and giant abalone eggs with regards to onset hatching time, hatching success rate, percentage of abnormality and survival rate.

Disk abalone (H. discus discus) and giant abalone (H. gigantea) eggs were obtained from Mie Prefectural Hatchery in Hamajima, Japan. For each species, 6 replicates per treatment were prepared and each replicate contained 90 eggs that were transferred into six-well plastic microplates and incubated at a temperature of 20 ± 1ºC under white light conditions of 12:12 h light/dark cycle. The effects of salinity change and exposure time on both species were tested by reducing the salinity from 34, 24 and 14 psu with exposure times of 0, 1, 3 and 6 h. The experiments were carried out for a period of 5 days.

Onset hatching time significantly increased for both species as salinity dropped and exposure time increased. Both abalone species followed a decreasing trend in terms of hatching success rate as exposure time increased at low salinity levels. As for abnormality, both species showed a significant negative effect of low salinity and long exposure times. Giant abalone showed more adaptability to long exposure time at low salinity levels compared to disk abalone, hence a higher survival rate.