title: Observations on the spawning behavior, egg masses and paralarval development of the ommastrephid squid Todarodes pacificus in a laboratory mesocosm.
abstract: The spawning behavior of ommastrephid squids has never been observed under natural conditions. Previous laboratory observations of Japanese flying squid (Todarodes pacificus) suggest that pre-spawning females might rest on the continental shelf or slope before they ascend above the pycnocline to spawn, and that the egg masses might settle in the pycnocline. Here, two mesocosm experiments were conducted in a 300 m(3) tank that was 6 m deep to investigate this hypothesis. In the first experiment, a thermocline (2.5-3.5 m) was established in the tank by creating a thermally stratified (17-22°C) water column. In the second experiment, the temperature was uniform (22°C) at all depths. Prior to spawning, females did not rest on the tank floor. In the stratified water column, egg masses remained suspended in the thermocline, but in an unstratified water column, they settled on the tank bottom, collapsed and were infested by microbes, resulting in abnormal or nonviable embryos. Eleven females spawned a total of 18 egg masses (17-80 cm in diameter), indicating that females can spawn more than once when under stress. Paralarvae hatched at stage 30/31 and survived for up to 10 days, allowing us to observe the most advanced stage of paralarvae in captivity. Paralarvae survived after consumption of the inner yolk, suggesting they might have fed in the tank.
authors.affiliation: School of Fisheries Sciences, Hokkaido University, 3-1-1 Minato-cho, Hakodate 041-8611, Japan puneeta83@gmail.com.
authors.forename: Pandey
authors.initials: P
authors.lastname: Puneeta
authors.affiliation: School of Fisheries Sciences, Hokkaido University, 3-1-1 Minato-cho, Hakodate 041-8611, Japan.
authors.forename: Dharmamony
authors.initials: D
authors.lastname: Vijai
authors.affiliation: School of Fisheries Sciences, Hokkaido University, 3-1-1 Minato-cho, Hakodate 041-8611, Japan.
authors.forename: Hae-Kyun
authors.initials: HK
authors.lastname: Yoo
authors.affiliation: School of Fisheries Sciences, Hokkaido University, 3-1-1 Minato-cho, Hakodate 041-8611, Japan.
authors.forename: Hajime
authors.initials: H
authors.lastname: Matsui
authors.affiliation: School of Fisheries Sciences, Hokkaido University, 3-1-1 Minato-cho, Hakodate 041-8611, Japan.
authors.forename: Yasunori
authors.initials: Y
authors.lastname: Sakurai
mesh_terms: D000818:Animals; D001522:Behavior, Animal; D049832:Decapodiformes / Q000196:embryology / Q000502:physiology*; D005260:Female; D008297:Male; D010063:Ovum / Q000502:physiology*; D012098:Reproduction; D013696:Temperature
keywords: Egg mass; Paralarvae; Spawning behavior; Thermocline; Todarodes pacificus