Release of eDNA by different life history stages and during spawning activities of laboratory-reared Japanese eels for interpretation of oceanic survey data

Abstract

To assist in detection of offshore spawning activities of the Japanese eel Anguilla japonica and facilitate interpretation of results of environmental DNA (eDNA) analysis in their spawning area, we examined the eDNA concentration released by each life history stage of artificially reared Japanese eels in the laboratory using quantitative real-time PCR (qPCR). We also compared eDNA concentrations between before and after artificially induced spawning activities. eDNA was not detected from three 30 L seawater tanks containing each single fertilized egg, but eDNA was found from other tanks each containing single individuals of larval stages (preleptocephalus and leptocephalus), juvenile stages (glass eel, elver and yellow eel) or adult stage (silver eel). The eDNA concentrations increased in the life history stages, showed a significant difference among all stages, and were positively correlated with the total length and wet weight. Moreover, the eDNA concentration after spawning was 10–200 times higher than that before spawning, which indicated that the spawning events in the ocean would produce relatively high eDNA concentration. These results in the laboratory suggested that eDNA analysis appears to be an effective method for assisting oceanic surveys to estimate the presence and spawning events of the Japanese eel in the spawning area.

The relationship between eDNA particle concentration and organism abundance in nature is strengthened by allometric scaling

“…While we demonstrate that incorporating allometric scaling coefficients 509 substantially improves models predicting abundance and eDNA concentration at the population 510 level, we have not directly quantified how eDNA production scales allometrically in brook trout 511 at the level of individual organisms. Nevertheless, recent experiments demonstrate that mass-512 specific eDNA production rates tend to decline as individual mass increases (Maruyama et al, 513 2014;Mizumoto et al, 2017;Takeuchi et al, 2019). We found that a scaling coefficient of 0.72 514 best described patterns of eDNA concentration for our study species across our nine study lakes; 515 this value closely aligned with the metabolic scaling coefficient for brook trout from (Hartman & 516 Cox, 2008).…”

“…If size classes exhibit different behaviour at high densities, this could further affect estimates of 551 allometric scaling. Future studies examining allometric scaling in eDNA production should 552 therefore incorporate individuals from a gradient of age/size classes and quantify organismal 553 eDNA production at the individual-level, as in (Takeuchi et al, 2019). Notably, the two studies 554 to examine eDNA production rates at an individual level across age/size classes found that 555 larger, older individuals exhibited lower mass-specific eDNA production rates ( Our results provide evidence supporting the hypothesis that eDNA production scales 568 allometrically with organism mass and can be modelled according to the power function: 569…”

“…208ASM was calculated by replacing the mass measure with mass 0.73 according to the 209 was included to account for the relative decline in mass-specific eDNA 213 production or excretion rates typically observed as individual organismal mass increases 214(Maruyama et al, 2014;Takeuchi et al, 2019;Vanni & McIntyre, 2016). Scaling coefficients 215 can vary substantially depending on the physiological process, taxonomy or environment 216(Allegier et al, 2015;Glazier, 2005).…”

“…Maruyama et al, 556 2014;Takeuchi et al, 2019). There is also a critical need to conduct such experiments in situ at 557 field study sites on wild organisms, as in (Pilliod, Goldberg, Arkle, & Waits, 2014).…”

The effect of activity, energy use, and species identity on environmental DNA shedding of freshwater fish

“…Under natural conditions, differences in fish physiology, diet and behavior are likely to affect this process and confound the interpretation of eDNA-based results from a water body (Klymus et al, 2015). For perch and eel, Maruyama et al (2014) and Takeuchi et al (2019), respectively, found lower eDNA shedding rates for adults in comparison to juveniles, which is likely caused by the ontogenetic decrease in metabolic rates (Winberg, 1960). However, these findings could not be confirmed in an experiment with a salmonid species (Mizumoto et al, 2018).…”