Evaluation of an improved RNA/DNA quantification method in a common carp (Cyprinus carpio Linnaeus 1758) larval feeding trial with Artemia , two nematodes (Panagrellus redivivus Linnaeus 1758, Panagrolaimus sp. Fuchs 1930) and dry feed

Abstract

Evaluation of an improved RNA/DNA quantification method in a common carp (Cyprinus carpio Linnaeus 1758) larval feeding trial with Artemia, two nematodes (Panagrellus redivivus Linnaeus 1758, Panagrolaimus sp. Fuchs 1930) and dry feed Summary The RNA/DNA ratio commonly used as proxy for the nutritional condition of fish larvae is affected by RNA degradation during analysis. For evaluation of two strategies to improve RNA integrity, a three-week feeding trial was carried out to assess the suitability of two nematode species (fam. Panagrolaimidae) as feed for newly hatched carp larvae (Cyprinus carpio) in comparison to Artemia nauplii (Artemia sp.) and a commercial dry feed. Aiming for an increased reproducibility of RNA/DNA determination, a high-salt inactivation (RNA later) as well as a targeted approach with a recombinant RNase inhibitor were compared to the classical protocol using lab chip technology. Improved RNA integrity was observed with high-salt inactivation when compared with a strategy applying a specific RNase inhibitor or the classic protocol. Carp larvae fed Artemia for 2 weeks and then dry feed for 1 week revealed the best overall growth performance as well as survival [83.0 AE 35.2 mg fresh weight (FW), 20.0 AE 2.4 mm total length (TL), 86.6 AE 11.7% survival]. Larvae fed the nematode species Panagrellus redivivus for 1 week and subsequently dry feed for 2 weeks (37.4 AE 29.1 mg FW, 14.7 AE 2.8 mm TL, 76.0 AE 6.0% survival) performed better than larvae fed with dry feed alone (28.2 AE 29.6 mg FW, 14.3 AE 2.9 mm TL, 54.3 AE 14.2% survival) or those receiving Panagrellus for 2 weeks. Between both nematode species, Panagrellus was a better feed with regard to growth performance and survival. RNA/DNA ratios ranged between 0.65 AE 0.27 (8 days post-hatch) and 1.96 AE 0.63 (22 days post-hatch) and were in the same treatment order as the other growth parameters. RNA/DNA ratios were significantly correlated with the growth rate, and decreasing RNA/DNA ratios in larger larvae may reflect decreasing growth rates with size rather than decreased nutritional status. Here, an improved RNA/DNA ratio protocol is presented in a feeding trial that reveals the suitability of nematodes as a first feed for common carp larvae.

Are meiofauna a standard meal for macroinvertebrates and juvenile fish?

“…Within the last 15 years, DNA-based procedures as well as stable isotope and fatty acid analyses of the characteristics of trophic networks have become well established (Traugott et al, 2013;Maghsoud et al, 2014). Genetically based examinations of the gut contents or feces of consumers are able to identify consumed organisms at a taxonomically high resolution (Pompanon et al, 2012;Tillner et al, 2015). In addition, approaches based on the use of stable isotopes or fatty acids can be applied to investigate trophic pathways, which allows the integration of meiofauna into benthic food webs, as shown by Goedkoop et al (1998) and Schmid-Araya et al (2016) for the meiofauna of streams and lakes.…”

The early catfish catches the worm: predation of Corydoras aeneus (Siluriformes, Callichthyidae) on freshwater nematodes

“…A massive consumption of meiofauna, and of nematodes in peculiar, by larvae and juveniles of bottom-feeding fishes has been only recently acknowledged through field and laboratory studies (Schlechtriem et al, 2004, Spieth et al, 2011, Weber and Traunspurger, 2014aTillner et al, 2015). The fish-nematode trophic channel consists in a predator-prey body mass ratio over 5 orders of magnitude, which is in the upper bound of predator-prey body mass ratios commonly found in freshwater ecosystems for ectothermic vertebrates (Brose et al, 2006).…”