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Title: Approach to Circular Economy through the inclusion of local agriculture by-products in fish feedstuff: consumer health risk assessment due to heavy metal accumulation and effects on fish health by study of liver and gut morphology
Authors: Mohamed Harb Rabia Hamad, Selwan 
Director: Ginés Ruiz, Rafael 
Castro Alonso, Pedro Luis 
UNESCO Clasification: 32 Ciencias médicas
Issue Date: 2023
Abstract: The circular economy refers to an industrial economy that is restorative by intention, designed for reducing the carbon footprint and employing a more sustainable and eco-friendly use of resources. For this purpose, sustainability and efficiency must be applied to agricultural practices by improving management and reducing waste of native crops and revalorizing it into a series of new value chains. New economic models must adapt to the requirements of sustainability brought about by climate change. The recycling of materials that still are valuable in their end-of-life phase and closing production loops are one way to use resources more efficiently and minimize the impact on the environment. This new way of thinking will promote bio-based industries for the recovery, transformation and revalue of by-products from the primary and secondary sectors. When formulating an aquafeed diet, the potentiality of each component must be evaluated not only from their productive responses but also from any synergic effects on the animal well-being, health and resistance. Moreover, possible contaminants related to plant growth or products and byproducts processing should be addressed. The current study aimed to determine the metal content of Aloe vera and banana by-products as sustainable alternatives to standard ingredients in aquaculture diets, develop diets with varying levels of inclusion of these by-products in accordance with the circular economy concept, validate diets for fish, and assess the accumulation of pollutants as well as various risk management strategies and nutritional value. Also, assess the effects of adding banana meal to the diet on the growth, biochemistry, and histomorphology of the liver and intestine in juvenile tilapia. In our study, two different plant by-products Aloe vera and banana crop by-products, as well as golden mullet (Liza aurata) and tilapia were evaluated (Oreochromis niloticus). For each of the byproducts, four isocaloric and isoproteic diets were made: one of them was a commercial diet customized to the species being studied, and the other three contained increasing amounts of the raw material: 5, 10, and 20% of banana by-products and 2, 4, and 6% of Aloe vera by-product. All diets were analyzed both for biochemical composition and content in metals. risks arising from fish metal content has been measured using various parameters as Estimated Daily Intake (EDI), Maximum Safe Consumption (MSCA), Target Hazard quotient (THQ), Hazard Index (HI) Carcinogenic risk of As (As- CR), the Value Selenium Health Benefit (Se HBV) and also the Nutritional Values has been evaluated.In both trails it was found that in the various ratios of Aloe vera and banana by-product in diets, the content of all elements was less than the upper limits permitted. According to the different riskbenefit analyses used by national and international authorities, consuming Liza aurata and Oreochromis niloticus is generally safe. Although there were detectable levels of potentially dangerous inorganic As, they were below safety guidelines, and Se-HBV values showed benefits to human health. In the third trail, the same technique by using the banana by-product with different inclusions in Nile tilapia diets but to evaluate the growth rate, proximal composition of the fish fillet and the effect on liver histology whence the level of vacuolization (steatosis), the presence of necrosis foci or pyknotic nuclei, nuclear pleomorphism, or the emergence of vascular alterations in the hepatic tissue and in the gut histology the height and width of the villi was measured. Moreover, the various fatty acids identification and quantitation was performed. The finding of this study clarified that the banana ensure that the tilapia would grow and perform adequately which the consumption of banana by-products increased the rate of growth, as measured by weight and length, both during the experimental test and after. During histological study, the feeding conditions had no adverse impacts on growth or proximal composition, and neither the liver nor the gut seemed to have any unusual effects. Moreover, the presence of banana by-product had no effect on the lipid content of tilapia liver, although there was a slight change in the foregut and hindgut folds. As a result, the banana by-product was shown to be an effective and environmentally safe way to feed Nile tilapia, which helps to reduce food loss and waste from a circular economy perspective. Our findings support the circular economy concept of employing Aloe vera and banana wastes as an alternative ingredient in fish feeding for Liza aurata and Oreochromis niloticus in order to lower the cost of the fish diets and ensure their safety for fish and humans.
Description: Programa de Doctorado en Acuicultura Sostenible y Ecosistemas Marinos por la Universidad de Las Palmas de Gran Canaria
Faculty: Facultad de Ciencias de La Salud
Appears in Collections:Tesis doctoral
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