Abstract
Burbot (Lota lota maculosa) are the only freshwater members of the Gadidae family and can be reared in similar water quality parameters as rainbow trout under controlled rearing conditions. Burbot have desirable fillets for consumers and demonstrate good growth performance in culture. As such, burbot are a favorable species for aquaculture and may have potential for polyculture in trout facilities to diversify production. To successfully develop burbot culture on a production scale, nutrient requirements in burbot feed should be evaluated. In this project, we aimed to determine growth performance of fish fed two dietary formulations (marine type or trout type) for economic burbot culture. Additionally, the digestibility of soy protein ingredients for burbot was investigated to address the potential to produce more sustainable diets for burbot production in the future.
To evaluate growth performance with commercial diet blends, a feeding trial was conducted, incorporating a marine-type commercial diet (Europa), marine-type formulated diet (Burbot1), trout-type commercial diet (Oncor) and trout-type formulated diet (Burbot 2).The experiment was conducted as a complete randomized design, with three replicate tanks per diet. No significant differences in growth parameters such as FCR, SGR, RG and K factor (p>0.05) were observed for burbot fed the different dietary treatments. There were no statistically significant difference between treatments. Taking these results into account it is suggested that a trout type dies such as Oncor would provide equal growth to a higher cost marine type diet and be a preferred choice for most producers at this life stage. There were significant differences observed between treatments for some organosomatic indices. Fillet yield of fish fed Burbot 2 diet was significantly lower than fish fed other diets (p=0.0039), and fish fed Oncor diet had the highest fillet yield level. This indicates that fish fed Burbot 2 diet may not have utilized dietary protein as efficiently for muscle creation in fillets, and fish fed the Oncor diet had the most efficient dietary protein usage. Also, gastrointestinal index (GII) was significantly higher in fish that fed with Oncor diet than fish fed Burbot 1 diet (p=0.0478). Proximate analyses showed that Oncor diet has the highest fiber level, and the highest GII in fish fed Oncor diet may be due to high fiber content in Oncor diet.
For burbot soy digestibility, soybean meal diet (SBM), soy protein concentrate diet (SPC), microbially enhanced soy protein diet (MESBM) and reference diet were used to feed adult burbot. 30% of fishmeal protein in reference diet was replaced with dietary soy protein ingredient in experimental diets (SBM, SPC, and MESBM). Also, yttrium oxide, an inert marker was added in all diets at 0.1% ratio in order to calculate the nutrient digestibility. The present study indicates that burbot can digest high soy protein diets, also there is a significant difference between treatment digestibility for burbot. Furthermore, the soy protein ingredient digestibility of burbot was high, and there were significant differences between treatments on soy protein ingredient digestibility. The SPC diet has the highest digestibility level (85.5%) and digestibility of soy protein ingredient in SPC diet is significantly higher than in MESBM diet (P= 0.0004), but there is no significant difference among the protein ingredient digestibility of the SBM diet and SPC diets. Therefore, SPC and SBM may serve as better soy protein ingredients compared to other soy ingredients for replacing fishmeal in burbot diets based on higher levels of apparent digestion coefficient (ADC).