Superoxide Production by the Red Tide-Producing Chattonella marina Complex (Raphidophyceae) Correlates with Toxicity to Aquacultured Fishes.

Tomoyuki Shikata,Kazuki Akita,Ryusuke Tanaka,Yasuhiro Yamasaki,Yoshitaka Nishiyama,Yuichiro Fujinami,Saho Kitatsuji,Koki Yuasa,Setsuko Sakamoto,Toshihisa Kotake

doi:10.3390/antiox10101635

Abstract

The marine raphidophyte Chattonella marina complex forms red tides, causing heavy mortalities of aquacultured fishes in temperate coastal waters worldwide. The mechanism for Chattonella fish mortality remains unresolved. Although several toxic chemicals have been proposed as responsible for fish mortality, the cause is still unclear. In this study, we performed toxicity bioassays with red sea bream and yellowtail. We also measured biological parameters potentially related to ichthyotoxicity, such as cell size, superoxide (O2•−) production, and compositions of fatty acids and sugars, in up to eight Chattonella strains to investigate possible correlations with toxicity. There were significant differences in moribundity rates of fish and in all biological parameters among strains. One strain displayed no ichthyotoxicity even at high cell densities. Strains were categorized into three groups based on cell length, but this classification did not significantly correlate with ichthyotoxicity. O2•− production differed by a factor of more than 13 between strains at the late exponential growth phase. O2•− production was significantly correlated with ichthyotoxicity. Differences in fatty acid and sugar contents were not related to ichthyotoxicity. Our study supports the hypothesis that superoxide can directly or indirectly play an important role in the Chattonella-related mortality of aquacultured fishes.

Highlights

When microalgae grow largely to change the water color in coastal areas, we call the phenomenon “red tide”
We first confirmed that all strains belonged to Chattonella by analyzing sequences of the large subunit (LSU) D1–D2 domain of rDNA (Figure 1)
It is necessary to determine the chemical(s) responsible for gill dysfunction to elucidate the mechanism of aquacultured fish mortality by Chattonella

Summary

Introduction

When microalgae grow largely to change the water color in coastal areas, we call the phenomenon “red tide”. The. Chattonella marina complex (hereafter referred to as Chattonella) is a marine raphidophyte that forms red tides, causing tremendous mortality of aquacultured organisms, mainly fish, in temperate coastal waters around the world [2,3]. Chattonella marina complex (hereafter referred to as Chattonella) is a marine raphidophyte that forms red tides, causing tremendous mortality of aquacultured organisms, mainly fish, in temperate coastal waters around the world [2,3] Chattonella antiqua, C. marina, C. ovata, and C. minima, which were formerly distinguished by morphological features [4,5,6,7,8]. In order to develop specific mortality mitigation techniques, it is necessary to determine the mechanism for the mortality of aquacultured fish by Chattonella. Studies over about 40 years have revealed that decreases in the blood oxygen level and osmotic injury

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