TI1E RIOLOQY OF PEl,A(ITC SHRIMPS IN THE OCEAN
27 1
September. The first clutch contains more eggs (average 83/fernale)
than the second (60 eggs), probably duc to reduction of the female
reproductive capabilities (Apollonio, 1969). Matthews and Pinnoi
state that Y. vruultidentata from the coast of western Norway breeds
throughout, most of year with indications of greater activity in MayJune and iii October. It iR mid that, after each spawning these species
carry egg8 for about five months till hatching.
In contrast, with the above-rnentio~~ed shrimps inhabiting the
epipelagic and upper mesopelagic zoneR, the spawning seaaon is not
restricted in time in lower meso- and bat hypehgic species. Probably,
spawning takos place during much of the year. Aizawa (1968) supposes
that the spawning of Acanthlph?yra quadrispinosa is prolonged from
Mttrch-April to November-Decembrr mtl thttt hatching takes place
between December and May. Off Bermuda, females carrying eggs with
advanced embryos and free-living young of several lower meso- and
bathypelagic ciwids are found throughout the year (Chace, 1940;
Gurney and Lobour, 1941). The absenoe of a marked seasonal breeding
period in femalca of the lower meso- and bathypelagic carids might be
related to the fceding habits of the early larvae; they do not feed on
phytoplankton in the euphotic zone but can probably use a wide
range of mctterial as food and adopt the diet of the adults fairly quickly.
Muuchline (1 972) cliscusud the preRence, or absence, of seasonal
breeding cycles in &thypelagic crustaceans. He showed the possibility
that, in bnthypelttgic species, the final stages of maturation of the
oviiry coulcl bo dependent upon mating having taken place, and
therefore the state of sexual maturit,y of males would provide evidence
as to whethor or not seasonal breeding occurs.
I n the early
spawning scasoii, however, females arid males tend to live separately,
and u marked diacrepancy in t8he Rex ratio occurs according to locality
in May-July (Omori, 1969a). Apparently the females swarm in shallower
neritic water than the males. Thc sex ratio of A~etrn~japonict~ and of
several penaeicls in the Ariake Scti also fluctuates during the spawning
season, and Ikenuitsu (1953) attributed this phenomenon to early
death of the males after copultrtion, because the ratio is generally
slanted towards females in the commercial catches. However, such
variation was not observed in A . japonicw in the &to Inland Sea
throughout the year (Yasuda el aZ., 1953).
Tho sex ratio of Sergia lucrns is generally 50: 60.
B. Development
Our hiowledge of the morphology of the larvae and juveniles of
pelagic shrimps is severely restricted by the practical difficulties of
27 1
September. The first clutch contains more eggs (average 83/fernale)
than the second (60 eggs), probably duc to reduction of the female
reproductive capabilities (Apollonio, 1969). Matthews and Pinnoi
state that Y. vruultidentata from the coast of western Norway breeds
throughout, most of year with indications of greater activity in MayJune and iii October. It iR mid that, after each spawning these species
carry egg8 for about five months till hatching.
In contrast, with the above-rnentio~~ed shrimps inhabiting the
epipelagic and upper mesopelagic zoneR, the spawning seaaon is not
restricted in time in lower meso- and bat hypehgic species. Probably,
spawning takos place during much of the year. Aizawa (1968) supposes
that the spawning of Acanthlph?yra quadrispinosa is prolonged from
Mttrch-April to November-Decembrr mtl thttt hatching takes place
between December and May. Off Bermuda, females carrying eggs with
advanced embryos and free-living young of several lower meso- and
bathypelagic ciwids are found throughout the year (Chace, 1940;
Gurney and Lobour, 1941). The absenoe of a marked seasonal breeding
period in femalca of the lower meso- and bathypelagic carids might be
related to the fceding habits of the early larvae; they do not feed on
phytoplankton in the euphotic zone but can probably use a wide
range of mctterial as food and adopt the diet of the adults fairly quickly.
Muuchline (1 972) cliscusud the preRence, or absence, of seasonal
breeding cycles in &thypelagic crustaceans. He showed the possibility
that, in bnthypelttgic species, the final stages of maturation of the
oviiry coulcl bo dependent upon mating having taken place, and
therefore the state of sexual maturit,y of males would provide evidence
as to whethor or not seasonal breeding occurs.
I n the early
spawning scasoii, however, females arid males tend to live separately,
and u marked diacrepancy in t8he Rex ratio occurs according to locality
in May-July (Omori, 1969a). Apparently the females swarm in shallower
neritic water than the males. Thc sex ratio of A~etrn~japonict~ and of
several penaeicls in the Ariake Scti also fluctuates during the spawning
season, and Ikenuitsu (1953) attributed this phenomenon to early
death of the males after copultrtion, because the ratio is generally
slanted towards females in the commercial catches. However, such
variation was not observed in A . japonicw in the &to Inland Sea
throughout the year (Yasuda el aZ., 1953).
Tho sex ratio of Sergia lucrns is generally 50: 60.
B. Development
Our hiowledge of the morphology of the larvae and juveniles of
pelagic shrimps is severely restricted by the practical difficulties of