Abstract
ABSTRACTThe cyclopoid copepod Apocyclops royi (Lindberg 1940) is one of two dominant mesozooplankton species in brackish Taiwanese aquaculture ponds. Periodically low n-3 polyunsaturated fatty acid (PUFA) content in seston could potentially be a limiting factor for zooplankton diversity. Apocyclops royi’s potential ability to biosynthesize n-3 PUFA was investigated through a short-term feeding experiment on four species of microalgae. Furthermore, we analyzed the expression of genes encoding putative fatty acid elongase (ELO) and desaturase (FAD) enzymes in A. royi on long-term diets of the PUFA-poor Dunaliella tertiolecta and the PUFA-rich Isochrysis galbana. The copepods exhibited high contents of docosahexaenoic acid (DHA, C22:6n-3) (>20% of total fatty acid) even when DHA-starved for two generations, and no significant differences were found in absolute DHA content between treatments. Transcripts correlating to the four enzymes Elovl4, Elovl5, Fad Δ5 and Fad Δ6 in the n-3 PUFA biosynthetic pathway were identified. Gene expression analysis revealed a significantly higher expression of two desaturases similar to Fad Δ6 in copepods fed PUFA-lacking algae compared to copepods fed algae with high PUFA content. These findings suggest a highly active n-3 PUFA biosynthesis and capability of DHA production in A. royi when fed low-PUFA diets.
Highlights
The tropical climate of Taiwan gives rise to abundant zooplankton communities in coastal waters (Dur et al, 2007; Hwang et al, 2003; Ju et al, 2018), rivers and estuaries (Hwang et al, 2010; Beyrend-Dur et al, 2013)
Fatty acid analyses Algae samples were labelled with species name while copepod samples were labelled with abbreviations of the algae diet, i.e. DUN, ISO, RHO and TET
Copepod fatty acid (FA) analysis was not done for the ISO treatment
Summary
The tropical climate of Taiwan gives rise to abundant zooplankton communities in coastal waters (Dur et al, 2007; Hwang et al, 2003; Ju et al, 2018), rivers and estuaries (Hwang et al, 2010; Beyrend-Dur et al, 2013). A case study has shown that adjacent man-made brackish aquaculture ponds in which copepods are reared as live feed for fish larval production reveal a rather simplistic zooplankton community (Blanda et al, 2015). This is despite periodical inoculation of zooplankton from nearby species-rich estuaries (Rayner et al, 2015; Yu, 2004).
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