The present study evaluated the use of Arthrospira platensis cyanobacterium and fish by-products as alternative protein sources in Liza aurata larvae of 31 dph (days post-hatching) with an initial weight and length of 1.92±0.12 mg and 10.47±1.01 mm, respectively. Five microdiets were tested: Control diet, with 100% protein from squid meal; Arth10, Arth20 and Arth40 diets with 10%, 20% and 40% A. platensis as partial substitution of squid meal; and Circular diet, with 100% squid meal substitution by fishery by-product. This research revealed that Spirulina can be included in the microdiet of mullets up to 40% maximum selected replacement, reporting high growth rates in size and weight, as well as high survival rates and resistance to stress. The inclusion of aquafeed by-products, despite reflecting significantly lower growth, it presented similar survival rates and proximal composition in L. aurata larvae. The skeletal anomalies analysis showed that mullet larvae do not present high percentages of severe deformities, except for the presence of stones in the urinary ducts. These results open a path towards sustainability for L. aurata production and the use of fisheries by-product resources, giving rise to a circular economy necessary for the aquaculture sector.
The continuous expansion of the aquaculture sector as well as the high demand of the population and the decreasing production of fishmeal and fish oils are speeding up the search processes for new raw materials and/or alternative protein and lipid ingredients to supply, effectively, proper feeding of cultured aquatic organisms. For this, the sector must focus on growing to offer products both in greater quantity and quality following the principle of sustainability of the environment and natural resources (FAO, 2022). Numerous scientific studies are directing their investigations towards the search for the highest percentage of fishmeal replacement by different routes and in a multitude of potential species for aquaculture industry (Yarnold et al., 2019). However, research on mugilids, candidate species for diversification, is scarce.
For this reason and taking into account that the exorbitant increase in prices will affect the composition of diets in the future and, therefore, the cultivation of species with high requirements, the species of Liza aurata has been selected. Omnivorous organism with a low trophic level that presents a high potential in terms of the use of alternative ingredients and by-products of low added value, as well as the potential that its cultivation presents in different environments and even extreme conditions, and the opportunity for introduction into the regional aquaculture production in a differentiated way from the rest (Crosetti and Blaber , 2016; Rosas et al., 2019a).
Therefore, the main objective of the work is to evaluate the effect and potential use of these ingredients as alternative protein sources to squid meals used in microdiets for weaning of Liza aurata larvae.
Material and methods
The trial was carried out in the Parque Cientifico Tecnológico de Taliarte (PCTM ) of the ECOAQUA University Institute of the University of Las Palmas de Gran Canaria.
Liza aurata larvae of 31 dpe (N=400) were randomly seeded in 15 200-L cylindrical tanks (5 treatments in triplicate). A co-feeding protocol was carried out with metanauplii of Artemia sp. and 5 different experimental microdiets according to the percentage of inclusion and replacement of squid meal by the cyanobacteria Arthrospira platensis in 10% (Arth10 Diet), 20% (Arth20 Diet) and 40% (Arth40 Diet) and by marine origin by-products not intended for human consumption (Sandach III) in 100% (Circular Diet). To evaluate the effect of the inclusion of the alternative ingredients, the larvae were measured (total length; mm) and weighed (wet weight; mg) to estimate parameters related to growth at 31, 40 and 52 dpe . Likewise, the proximal composition and fatty acids of the auxiliary cultures used during larval rearing, enrichers, experimental microdiets and larvae were analyzed following standardized chemical procedures (AOAC , 2005). In addition, larval quality was evaluated by performing a test of activity and resistance to an increase in salinity (38 to 70 ppt) and an analysis of identification and quantification of severe skeletal anomalies along the vertebral axis described by Boglione et al., (2014).
Results and discusión
The larvae fed with Arth10, Arth20 and Arth40 spirulina-based microdiets showed growth performance similar to the Control diet and significantly higher than the Circular diet. However, all treatments present high survival rates, greater than 90%, and similar values in the proximal composition as those found by Rosas et al. (2019a) in Mugil Liza . Larvae fed high levels of squid meal substitution exhibited a similar stress response as those fed the Control diet. On the other hand, the increasing inclusion of alternative ingredients to squid meal reflects a tendency to decrease the percentage of severe skeletal anomalies and, therefore, to increase the total percentage of high-quality larvae.
These results demonstrate the robustness of the larvae and the feasibility of producing juveniles with more sustainable diets, in addition to contributing to the promotion and growth of complementary industries, as well as the future development of the sector based on the sustainability of the environment and resources.
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Rosas, V. T., Bessonart , M., Romano, L. A., and Borges, M. (2019a). Fishmeal substitution for Arthrospira platensis in juvenile mullet ( Mugil liza ) and its effects on growth and non-specific immune parameters. Revista Colombiana de Ciencias Pecuarias, 32(1), 3-13.
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