Eugenia Zuasti

Tenebrio molitor (TM) meal is a potential alternative ingredient to plant and fishmeal in aquafeeds due to its high protein content, digestibility, and low environmental impact. However, its low n-3 PUFA (EPA and DHA) content represents one of its main limitations. This study evaluated the effects of replacing fishmeal and plant-derived ingredients (plant proteins and soybean oil) with full-fat TM meal on the growth performance and lipid composition of tissues in juvenile European seabass (Dicentrarchus labrax). Four experimental diets, including 5–10% TM for replacing fishmeal and soybean oil (FM5 and FM10) and 10–20% TM for substituting plant protein ingredients and soybean oil (PI10 and PI20), were tested over 49 days against a control diet (CT). Fish fed on PI20 exhibited the highest growth performance (final weight: 49.73 g and SGR: 1.78% day−¹) compared to fish fed on FM (final weight: 47.0 g and SGR: 1.62% day−¹) and CT (final weight: 48.45 g and SGR: 1.71% day−¹). In general, the diets containing TM modulated the lipid profile in fish tissues by reducing the liver lipid content and muscle triglycerides and increasing the n-3/n-6 ratio compared to the CT diet. However, the most effective approach for modulating those parameters seems to be using the TM meal for replacing the plant ingredients instead of substituting fishmeal. Moreover, this feeding strategy, demonstrated to be useful for promoting the growth of fish owing to the use of the TM meal for replacing fishmeal, resulted in a slight reduction in the final weight of the fish.

Alternative prophylactic strategies to limit farm animal infection are needed in order to avoid the use of antibiotics. Anti-bacterial and immunostimulatory properties of bioactive compounds are of great interest in aquaculture. Marine derived polysaccharides, such as chitosan and ulvan, together with nanotechnology, have become the focus of attention in the scientific community due to their wide range of biological properties. In this work, chitosan and ulvan-loaded chitosan nanoparticles (referred as CS-TPP NPs and CS-UL-TPP NPs, respectively), obtained by the ionotropic gelation method, had round shape, and the mean sizes were 137.00 ± 5.44 and 325.50 ± 4.95 nm, respectively. No study about the anti-bacterial activity of both types of NPs against Photobacterium damselae subsp. piscicida, an important fish pathogen, has been reported so far. Furthermore, the potential immunostimulatory effects of CS-UL-TPP NPs after oral administration in fish have not yet been evaluated. The percentage of bacterial inhibition against P. damselae subsp. piscicida was determined through in vitro assays, and it was significantly higher in CS-UL-TPP NPs than in CS-TPP NPs at concentrations below 0.03 mg mL⁻¹. The effects on the immune system of CS-TPP and CS-UL-TPP NPs were evaluated in Solea senegalensis juveniles at 30 days after oral administration. Lysozyme activity as well as gene expression levels of il1b, il6, hamp1, tf and c3 was significantly higher in CS-UL-TPP NP-treated groups than in the controls, and no significant differences were observed in CS-TPP NP-treated groups. Thus, ulvan extracted from the macroalgae Ulva ohnoi could improve anti-bacterial and immunostimulant properties of CS-TPP NPs thereby making them suitable to be used as vaccine adjuvant or as immunostimulant.