Introduction
Morden aquaculture has been decoupled from using fish meal as one of the major ingredients for aquafeeds. Many aquafeed producers now use soy and corn-based proteins, often associated with sub-optimal growth and feed efficiency, increased land and water use, and aquaculture carbon-foot print. These non-local resources have generated new ecological and socio-economic issues [1].
Macroalgae are a readily available resource with moderate protein and high fiber, minerals, antioxidants, and vitamin content. Production of macroalgae does not rely on land and freshwater use and may also be harvested from coastal regions with minimal environmental impact. Several authors have studied the inclusion of macroalgae in diets, concluding that high (>10%) dietary incorporation of macroalgae negatively affected growth and feed utilization parameters. Authors support that disruption of the macroalgae cell wall may increase nutrient bioaccessibility and access to the digestive enzymes, favoring nutrient absorption efficiency and fish growth. Adequate physical, chemical, enzymatic, and/or fermentation treatments may be required to disrupt the macroalgae extracellular polysaccharides matrix [2,3].
Codium tomentosum natural distribution included Europe and North Africa. It has also been successfully produced as an extractive species in integrated multi-trophic aquaculture systems (IMTA), including in Portugal. Codium tomentosum has a relatively higher protein level, circa 20-25%, but its potential as an aquafeed ingredient has been little studied. The present work aims to investigate the potential of alkaline hydrothermal pre-treatment of Codium tomentosum to increase its viability as an ingredient in diets for European seabass.
Material and Methods
Treatment of macroalgae
Samples of Codium tomentosum were provided from AlgaPlus, Aveiro, Portugal. Codium tomentosum was mixed with water (control) or NaOH (0.5N and 1N; solid-liquid ratio of 4:3) and autoclaved (121ºC) for 30 and 60 min. All the samples were analyzed for neutral detergent fiber (NDF), acid detergent fiber (ADF), crude protein, soluble protein, and phenols.
Growth trial
Four experimental diets were formulated to be isoproteic (48% dry matter basis) and isolipid (18% dry matter basis). A practical diet was used as a control diet (D1), and three other diets were formulated to include 7.5% Codium tomentosum at the expense of a mixture of soybean and wheat meal, namely non-treated Codium (D2), autoclaved for 30 min with 1N NaOH (D3), and autoclaved for 60 min with 1N NaOH (D4). The growth trial was conducted in a RAS system equipped with 12 tanks of 500 L water capacity, thermoregulated to 22 ºC. 192 acclimatized European seabass juveniles (IBW of 38 g) were divided into 12 groups and fed each experimental diet in triplicate, twice a day until satiation, 6 days a week, for 11 weeks.
Results
Irrespective of autoclave time exposure, Codium tomentosum soluble protein, and phenols content were significantly increased, while crude protein, NDF, and ADF significantly decreased when mixed with NaOH 1N than with NaOH 0.5N. These results suggested that the combined alkaline (NaOH 1N) with hydrothermal treatment (for 30 or 60 min) disrupted the cell wall of macroalgae being chosen to be incorporated as an ingredient in diets for European seabass.
At the growth trial, it was observed that all the diets were well accepted by the fish, and mortality was low and not influenced by the diets. Dietary inclusion of 7.5% of untreated Codium tomentosum did not affect overall growth performance, feed intake, and feed utilization efficiency. However, relative to the control diet, the dietary inclusion of 7.5% Codium tomentosum treated with NaOH 1N and autoclaved for 30 min significantly increased growth performance and feed and protein efficiency ratio. In contrast, the Codium tomentosum treated with NaOH 1N and autoclaved for 60 min resulted in similar growth performance and feed utilization efficiency to the control diet, which was significantly lower than that obtained for the Codium tomentosum treated with NaOH 1N and autoclaved for 30.
In conclusion, the pre-treatment of Codium tomentosum with NaOH 1N and autoclaved for 30min significantly improved the potential of Codium tomentosum as a local and complementary feed ingredient for carnivorous fish species.
Acknowledgment
This work was funded by the R&D&I project MB, reference 06587.PTDC, funded by Fundação para a Ciência e Tecnologia (FCT). Ramos-Oliveira C and Filipe Diogo were supported by an FCT grant (2021.04809.BD, 2020.05525.BD, respectively).
Bibliography
[1]doi.org/10.1016/B978-0-12-821598-2.00003-5; [2]doi.org/10.1016/j.sjbs.2015.11.010; [3] doi.org/10.1111/j.1439-0426.2007.01017.x