Structure and properties of the egg mass of the ommastrephid squid Todarodes pacificus

Abstract

The Japanese flying squid, Todarodes pacificus, is thought to spawn neutrally buoyant egg masses that retain a specific location in the water column by floating at the interface between water layers of slightly different densities. It is important to understand the physical process that determines the vertical distribution of the egg masses to predict their horizontal drift in relation to embryo survival and subsequent recruitment. Here, mesocosm experiments were conducted in a 300 m3 tank by creating a thermally stratified (17–22°C) water column to obtain egg masses. A cage net methodology was developed to sustain egg masses for detailed observation. We measured the density of the egg masses of T. pacificus, and used this information to infer the vertical distribution patterns of the egg masses at the spawning grounds (Tsushima Strait, Japan). When measured separately, the density of the outer jelly of each egg mass was 2.7 σ units higher than that of the surrounding water. The outer jelly and the specific gravity of embedded individual eggs (~1.10) cause the egg masses to have very slight negative buoyancy relative to the water in which they are formed. Analysis of the vertical profile of the spawning ground showed that water density (σθ) increased sharply at ~30 m depth; thus, egg masses might settle above the pycnocline layer. In conclusion, we suggest that T. pacificus egg masses might retain their location in the water column by floating at the interface between water layers of slightly different densities, which happen to be above the pycnocline layer (actual depth varies seasonally/annually) in the Tsushima Strait between Korea and Japan.

Ommastrephid squid spawning in the North Sea: oceanography, climate change and species range expansion

“…Another successful example of ommastrephid squid adaptation to shallow water seas with semiclosed circulation is Todarodes pacificus, an ecological equivalent of Illex that lays its eggs in the Tsushima Strait, to be developed in the pycnocline and brought into the Sea of Japan with warmer and more saline water of the Kuroshio, the Tsushima Current and the East Korea Warm Current along Japanese coast (Puneeta et al 2017). The returning branch is composed of the Liman, North Korea and Central Japan Sea currents, which bring fresh and cold water along the Asian coast to the south (Uda and Morgan 2020).…”

In situ recordings of large gelatinous spheres from NE Atlantic, and the first genetic confirmation of egg mass of Illex coindetii (Vérany, 1839) (Cephalopoda, Mollusca)

“…In addition, the spheres most likely have a short-life span. Life span of spheres spawned and reared in aquaria (between 40 and 120 cm in diameter) of Todarodes pacificus (Steenstrup, 1880) is 5–7 days, with the smallest disintegrating first 38 .…”

Ecological-Fishery Forecasting of Squid Stock Dynamics under Climate Variability and Change: Review, Challenges, and Recommendations

“…Pelagic egg masses of ommastrephid squid are protected from pelagic zooplankton, hence their survival depends on environmental conditions. Squid actively choose the most appropriate locations to extrude their egg masses (Puneeta et al 2017). Although the temperature tolerance for normal embryonic development is quite wide (e.g., between 4 and 20°C for Illex squid (Hendrickson and Holmes, 2004)), the optimum temperature range is usually narrower (~ 3°C).…”

“…All ommastrephid squid extrude their eggs within voluminous, gelatinous egg masses that protect the embryos from predation by pelagic zooplankton (Puneeta et al, 2017). The pelagic egg masses are found in spawning grounds that are usually located in low latitudes to allow the eggs and paralarvae to develop and grow faster in warmer waters.…”