Variation of Nitrogenous Compounds in the Mass-Production Ponds of Swimming Crab Portunus trituberculatus Larvae with Particular Reference to the Survival Rate

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  • 種苗生産池中の窒素化合物の挙動からみたガザミ生産成績の違いについて
  • シュビョウ セイサンチチュウ ノ チッソ カゴウブツ ノ キョドウ カラ ミタ

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Abstract

Measurements of nitrogenous compounds of various forms (NH4-N, NO2-N, NO3-N and PON) were carried out in three different pond waters, i. e., green water (G) composed of green algae (mainly Nannochloropsis sp.), brown water (B) composed of natural diatom assemblage, and B+G water the mixture of them, during the rearing period of swimming crab Portunus trituberculatus larvae in 1991 at Hiroshima Prefecture Fish Farming Center. These results were investigeted in comparison with the survival rate of the larvae. Among three waters, the highest concentrations of the nitrogenous compounds and chlorophyll a were observed in Pond G and the lowest in Pond B. Sediment trap experiment made clear that the maximum downward flux of PON and chlorophyll a occurred in Pond G and the minimum in Pond B. The survival rate of crab larvae was generally higher in Pond B than Pond G in 1989-1991. The reason of the low survival rate in Green Water is supposed to be due to the higher concentration of NH4-N resulted from the excessive growth and the decomposition of green algae.

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