Effects of different temperature exposure on Oreochromis niloticus juveniles fed with a handmade diet

• Autor(a) principal: Pires, Sílvia Fabíola Saraiva
• Data de Publicação: 2022
• Tipo de documento: Dissertação
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: http://hdl.handle.net/10773/33947
• topic: Nile tilapia; Community-based aquaculture; Sustainability; Handmade diets; Antioxidant defenses

It is estimated that by 2050 the world population will reach 9.6 billion people. The main challenge facing this potential demographic growth is the need to increase food production, in the context of ecosystem protection, reduction of the greenhouse effect, and cultivation of species in a scenario of climate change. Furthermore, half of the population growth will occur in sub-Saharan Africa where a quarter of the population is undernourished. Aquaculture stands out for the production of food resources, under controlled conditions, aiming to be a sustainable practice. However, one of the biggest constraints in this industry is related to the production of carnivorous species that require diets with large amounts of animal protein. Therefore, is crucial to invest in the production of low trophic level species and identify new strategies to minimize the use of animal protein in the diets used in aquaculture, safeguarding sustainable practices. These factors are particularly important in developing countries with low technological resources. Another important factor that directly affects aquaculture production is the temperature fluctuations caused by climate changes. As ectothermic organisms, fish are expected to be at high risk in face of the current climate crisis due to their inability to use metabolic heat to maintain body temperature, making them susceptible to temperature fluctuations. This work addresses community aquaculture, aiming to increase income, employment level, and locally available food resources in local villages with few resources and limit access to animal protein. Thus, it is essential that this activity is designed according to the needs and limitations of local populations. In most community tilapia farms in Mozambique, fish are farmed exclusively on food that naturally grows in the culture ponds or supplemented with unsuitable and unbalanced foods for the species, such as leaves from local plants. Therefore, the following objectives were considered: (1) evaluation of the growth performance of tilapia juveniles fed the handmade diet formulated with local ingredients from Mozambique; (2) evaluation of the effects of temperature variations on tilapia juveniles with different sizes, fed a commercial diet and handmade diet, when exposed to three different temperatures (18, 26 and 32 ºC); (2.1) evaluation of genetic damage through comet assays, erythrocytic nuclear abnormalities (ENA) and erythrocytic maturity index (EMI); (2.2) evaluation of the neurophysiological and antioxidant activity; (2.3) assessment of the energy budget. Regarding the growth trials, tilapia fed with experimental diet present lower growth rates compared to the tilapia fed with control diet. The fish showed no differences between them regarding the DNA damage evaluated by the comet's assay. At the chromosomal level, fish fed commercial diet present higher damage values at 18 ºC in the trial performed with smaller tilapia. Regarding the IME, it was possible to verify a higher rate of cell renewal in fish fed the experimental diet. Besides, it is possible to conclude that fish fed the experimental diet presented higher levels of neurophysiological activity and higher antioxidant activity leading to increased oxidative stress. Regarding the energy budget, in both trials’ tilapia fed with experimental diet present higher values of cellular energy allocation at 18 and 32 ºC compared to the group fed commercial diet. These trials were carried out only for 24 hours, so in the future, it would be important to conduct more tests, of longer duration and with larger tilapia, to understand if the performance of fish fed with the handmade diet can improve since as fish grow their nutritional requirements change and also end up having different tolerance to stress.