Gas to protein: Microbial single cell protein is an alternative to fishmeal in aquaculture.

Methanotrophic bacteria represent an appealing opportunity to convert methane, a potent greenhouse gas, into a highly nutritious animal feed ingredient, single-cell protein (SCP). SCP has a comparable or superior nutritional profile that to most conventional protein sources and can be produced within a lower environmental footprint. The present study investigated the effect of replacing fishmeal (FM) with methanotrophic SCP in diets for barramundi (Lates calcarifer), a carnivorous fish with a high demand for dietary protein and energy. Dietary inclusion levels of 0 %, 10 %, 20 % and 30 % SCP (representing 0, 25, 50 and 75 % FM replacement) were tested, with and without additives. Triplicate groups of juvenile barramundi were fed the diets over 31 days. The inclusion of SCP significantly improved weight gain and feed conversion efficiency (FCE). Dietary SCP inclusion supported good gut health, with decreasing trends of hepatosomatic index, improved plasma biochemistry, and no adverse histopathological changes. Barramundi fed the SCP diets showed an intact intestinal barrier and a significant improvement in villi and lamina propria area when fed the additive supplemented SCP diets. This study demonstrates that this SCP is highly palatable to barramundi (even without dietary additives) and can replace up to 75 % FM with significant improvements in growth and FCE.

Effects of Formulation on the Palatability and Efficacy of In-Feed Praziquantel Medications for Marine Finfish Aquaculture.

Praziquantel (PZQ) provides an effective treatment against monogenean parasitic infestations in finfish. However, its use as an in-feed treatment is challenging due to palatability issues. In this study, five formulations of PZQ beads (1−4 mm) were developed using marine-based polymers, with allicin added as a flavouring agent. All formulations attained PZQ loading rates ≥74% w/w, and the beads were successfully incorporated into fish feed pellets at an active dietary inclusion level of 10 g/kg. When tested for palatability and digestibility in small yellowtail kingfish, the PZQ-loaded beads produced with alginate-chitosan, alginate-Cremophor® RH40, and agar as carriers resulted in high consumption rates of 99−100% with no digesta or evidence of beads in the gastrointestinal tract (GIT) of fish fed with diets containing either formulation. Two formulations produced using chitosan-based carriers resulted in lower consumption rates of 68−75%, with undigested and partly digested beads found in the fish GIT 3 h post feeding. The PZQ-loaded alginate-chitosan and agar beads also showed good palatability in large (≥2 kg) yellowtail kingfish infected with gill parasites and were efficacious in removing the parasites from the fish, achieving >90% reduction in mean abundance relative to control fish (p < 0.001). The two effective formulations were stable upon storage at ambient temperature for up to 18 months, showing residual drug content >90% compared with baseline levels. Overall, the palatability, efficacy and stability data collected from this study suggest that these two PZQ particulate formulations have potential applications as in-feed anti-parasitic medications for the yellowtail kingfish farming industry.

Bioavailability and palatability of praziquantel incorporated into solid-lipid nanoparticles fed to yellowtail kingfish Seriola lalandi.

In an effort to overcome the palatability issues currently constraining the effective delivery of praziquantel (PZQ) via feed to treat monogenean parasites in yellowtail kingfish, this study compared the bioavailability and palatability of PZQ in hydrogenated castor oil (HCO) solid lipid nanoparticles (SLN) against pure PZQ in this species. Improving bioavailability would facilitate lower dietary inclusion levels to achieve the same therapeutic dose and therefore reduce the bitterness of feeds containing PZQ. Bioavailability was determined by co-administering feed with either pure PZQ, HCO-SLN or HCO-SLN coated with chitosan via intubation and quantifying the pharmacokinetics response. In contrast to studies with mammals, the results demonstrated that PZQ in HCO-SLN had equal bioavailability to pure PZQ in yellowtail kingfish, including when HCO-SLN were coated with chitosan. We hypothesise that the lack of improvement in bioavailability may be due to the lack of M cells and Peyer's patches in fish and the subsequent inability of fish to take nanoparticles directly into the lymphatic system. Furthermore, palatability of the feeds medicated with PZQ was not improved when the PZQ was incorporated into HCO-SLN, possibly due to the low loading rate of PZQ within the HCO-SLN and the subsequent thick coating of nanoparticles that was required on the surface of the feed pellets. Combined, these data demonstrate that the SLN used in the current study are not capable of delivering the benefits required to enable effective in-feed treatment of PZQ against monogenean parasites in yellowtail kingfish.