Browsing by Author "Opio Alfonse"

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    Effects of environmental temperature on the growth performance of a tropical Oreochromis esculentus (Graham, 1928). Implications for the species conservation
    (Willey., 2022-09-14) Nagayi, Kalule Yawe jane; Kisakye Joseph; Tenywa Mwanja Matthew ,; Nattabi. Juliet; Opio Alfonse
    Climate variability and change are currently recognised global challenges. However, the impacts of rising temperatures may be greatest on tropical freshwater fish, which already exist in warm environments and may be living close to their critical thermal maximum. However, there is limited species- specific information on tropical species’ adaptive capacity to increased temperature. This study examined various growth attributes in juvenile populations (farmed, L. Kacheera and L. Nabisojjo) of a critically endangered tropical Oreochromis esculentus to determine its adaptive potential. Fish were acclimated at 25, 28, 31 and 34°C for 28 days. Overall, survival rates were high. Growth coefficient b was not significantly different from three (b = 3) in all treatments, implying isometric growth. The specific growth rates (SGRs), body condition K, and hepato- somatic indices (his) declined as the acclimation temperatures increased. Although SGR showed significant variations only among populations, the highest in L. Nabisojjo, K and HSI showed significant variations among treatments. Overall, the growth attributes declined at higher acclimation temperatures, but remained within acceptable ranges, implying that the species may attain normal growth at elevated temperatures experienced in outdoor aquaculture systems, despite its warm environmental background. Hence, we recommend selective breeding for temperature resilience and species introduction into aquaculture using broodstock from L. Nabisojjo.
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    Effects of thermal acclimation and ecological background on the physiological responses of juvenile Oreochromis esculentus (Graham, 1928). Implications for the species adaptive capacity to global warming
    (Aquaculture Research, 2021-10-12) Nagayi, Jane Kalule Yawe; KisakyeJohn , Joseph; Tenywa Mwanja, Matthew; Nattabi; Opio Alfonse
    Climate change is a recognized global concern in the 21st century. Water temperature elevation is likely to affect fish physiological and ethological function, causing great economic losses for fisheries resources and aquaculture production. Fish are particularly vulnerable to climate change as they are unable to control their body temperatures with changes in environmental temperature. This study assessed the effects of thermal acclimation in three juvenile populations of Oreochromis esculentus on the critical thermal maximum CTmax, cortisol, biochemical and haematological responses to acute temperature increase (0.3°Cmin−1). Fish from Senya farm, Lake Kacheera and Lake Nabisojjo were acclimated at 25°C, 28°C, 31°C and 34°C for 21 days at Kajjansi aquaculture research and development centre KARDC. The CTmax and blood cell counts increased, while plasma cortisol, glucose and proteins decreased at higher acclimation temperatures. Two-way ANOVA showed significant differences among treatments in CTmax, cortisol, proteins and erythrocytes indices, but not in glucose and leucocytes. However, significant variations among populations were only showed in CTmax. Overall, these results suggest that O. esculentus can respond to higher climate change induced temperatures, when allowed time for acclimation. Since temperature adaptation not only depends on the parameters assessed in this study, we recommend further investigations into metabolic rate and digestive enzymatic activity.