No abstract

Panagrolaimus sp. strain NFS-24-5 has potential to be used as live food for early stages of fish and crustacean species in marine aquaculture. One constraint to its commercialisation is the lack of a method that enables storage of nematodes over a longer time span. The objective of this study was to develop a procedure to transfer nematodes into a dormant state by desiccation. The nematodes were concentrated at densities of 25, 50, 100 and 200 x lO'' individials cm~^ on nylon net or cellulose paper, preconditioned for 72 h at 97.3% relative humidity (RH) and then stored at 52.9 or 32.8% RH for 1 week. Cellulose was a better carrier for the nematodes. Survival of the nematodes was reduced only at the highest nematode density on both materials. The water activity of desiccated nematodes was 0.44 and 0.33 at 52.9% and 32.8% RH, respectively, well beyond a point to prevent microbial growth. After storage over a period of 10 weeks at 25 x lO-* nematodes cm~^ at 52.9 and 32.8% RH, 92% of the nematodes were still alive. Monitoring the size distribution revealed no changes at 52.9%; RH, but there were more of the larger nematodes dying at 32.8% RH in two out of three experiments. The method can be used to store quiescent Panagrolaimus sp. (strain NFS-24-5) for transportation and use in small scale feeding experiments for marine fish and crustacean larvae.

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.