Mulata spawning analysis in 2005 and 2006

The comparison of Mulata spawning in 2005 and 2006 as below.

Wild captured G. nigra are rearing at UNAPDCM since 2002 and it starts spawned from 2002. Seven females (biomass 14,056 g) spawned 9,551,611 eggs with 83 times spawning under water temperature 15.8 ± 0.89 °C from July 13 to November 1, 2005. Spawned egg consist 6,956,117 floating eggs (72.8%) and it produces 4,487,154 hatch-out larvae (64.5%). Six females (biomass 13,035 g) spawned 15,657,954 eggs with 94 times under 16.5 ± 0.63 °C from June 11 to October 17, 2006. Spawned egg consist 7,947,405 floating eggs (50.8%) and it produces 5,422,681 hatch-out larvae (68.2%).

G. nigra spawn several times in a spawning season and the spawning quantity per fish body weight shows 679,500 eggs/Kg in 2005 and 1,202,224 eggs/Kg in 2006. The strong relation shows between egg quantity and the average water temperature while 3 days before spawning and it abundant at WT 15.50 °C in 2005. It has more spawning quantity at 16 °C in 2006, but floating egg rate is low. It may suggests high temperature affect egg or sperm quality and egg development.

天然魚Graus nigra のメス７尾（１４．１Kg) は、アルツーロプラト大学海洋科学部にて２００２年より飼育され、２００５年７月１３日から１１月１日において８３回（９５５万粒）の産卵が平均水温１５．８±０．８９℃でおこなわれた。この卵から６９６万粒（７２．８％）の浮上卵と４４９万尾の孵化仔魚（６４．５％）が得られた。２００６年６月１１日から１０月１７日にかけて、６尾のメス（１３．０Kg)が９４回にわたり産卵をおこない１５６６万粒の卵が得られた。この卵より７９５万粒（５０．８％）の浮上卵と５４２万尾（６８．２％）の孵化仔魚がえられた。

G. nigraは多回産卵魚で、魚体重あたり６８万粒/kg（２００５年）と１２０万粒/Kg （２００６年）の産卵をおこなった。２００５年では産卵前３日間の平均水温と産卵量において最も強い関係が見られ、１５．５℃において最も多くの産卵が見られた。２００６年では２日間から８日間において関係の強弱は見られず、１６℃において多くの産卵が見られた。