Trout challenge experimental design

Unvaccinated rainbow trout juveniles were purchased from Truchas de Leiza SL (Leiza, Navarra, Spain), and transported to IRTA research facilities in la Ràpita (Tarragona, Spain). Trouts were acclimated during two weeks in a 6 m3 tank connected to a water recirculation system (IRTAmar™). After the end of the acclimation period, all fish (N = 720) were individually measured and randomly distributed in 20,500-l tanks (n = 30 fish per tank; 4 replicate tanks per diet) connected to an IRTAmar™ unit with mechanical, biological filtration and UV water treatment. At the beginning of the trial, rainbow trout juveniles weighted 11.3 ± 0.2 g (mean ± standard deviation) body weight (BW) and measured 9.0 ± 0.1 cm in standard length (SL).

The trial was divided in two different parts, a nutritional trial that lasted 83 days during which the impact of experimental diets was evaluated in terms of KPIs associated to growth and feed performance. This was followed by a challenge trial with a pathogenic bacterium (Aeromonas salmonicida subsp. salmonicida), the causative agent of furunculosis, to evaluate the immunological competence of fish fed the experimental diets (15 days).

During the nutritional and bacterial challenge trials, water quality parameters were daily monitored with following results: water temperature (15.2 ± 1.2 °C), dissolved oxygen (8.6 ± 0.4 mg/l) (OXI330, Crison Instruments, Spain) and pH (8.2 ± 0.1) (pHmeter 507, Crison Instruments). Ammonia (0.17 ± 0.14 mg NH4+/l) and nitrite (0.22 ± 0.2 mg NO2/l) levels (HACH DR 900 Colorimeter, Hach Company, Spain) were weekly controlled. Photoperiod followed natural changes according to the season of the year (November to February). Diets were distributed using automatic feeders (ARVO-TEC T Drum 2000; Arvotec, Huutokosk, Finland) at a feeding rate of 3.0% of the stocked biomass, which approached apparent satiation. The daily feed ratio was evenly distributed in 2 meals at 08:00 and 13:00 h (at each meal, the corresponding feed ration was distributed during 1 h). Two hours after each meal, uneaten pellets were collected, dried overnight (120 °C) and weighted (g) for calculating daily feed intake values, while feed ration was adjusted to guarantee 10–15% of uneaten pellets; thus, confirming that fish were fed ad libitum.

Alberto Ruiz, Ignasi Sanahuja, Nana W. Thorringer, Julie Lynegaard, Eleni Ntokou, Dolors Furones, Enric Gisbert. (2023) .Single cell protein from methanotrophic bacteria as an alternative healthy and functional protein source in aquafeeds, a holistic approach in rainbow trout (Oncorhynchus mykiss) juveniles. Aquaculture, Vol 576, p.739861.

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