Dietary aloe and garlic crude polysaccharides: Effects on growth performance, haematological, and body composition parameters of Clarias Gariepinus

A dissertation submitted in fulfilment of the requirements for the Degree of Doctor of Philosophy (Fisheries and Aquatic Sciences)

Fish health management in aquaculture is one of the main challenges across the globe (including Namibia), worsened especially by the wide adoption of intensive farming systems. Nowadays, attention is focused on the use of medicinal herbs as alternative to unsustainable pharmaceutical drugs in aquaculture. This study aimed to develop andintroduce phytogenic diets made up of aloe vera (Aloe vera), and garlic (Allium sativum)crude polysaccharide extracts (separately and in mixture), which would promote growth, feed utilization, health, meat quality, and increase resistance against stress in African catfish, Clarias gariepinus reared in intensive aquaculture systems. First, this study evaluated the effects of dietary A. vera crude polysaccharides on growth performance, feed utilization, haemato-biochemical parameters, and resistance against low water pH in African catfish fingerlings. Fish were divided into five triplicate groups before being fed feeds supplemented with control 0%, 0.5%, 1.0%, 2.0% and 4.0% A. vera for 60 d. Fish fed a 1.0% A. vera supplemented diet showed a significant increase in all growth parameters compared to the control (P < 0.05). The protein efficiency ratio (PER) was significantly higher in fish fed 1.0% A. vera supplemented diet (1.31 0.22) compared to unsupplemented fish (0.85 0.10) and those fed 4.0% A. vera supplemented diet (0.85 0.14) (P < 0.05). The optimal dietary A. vera polysaccharide crude extract requirement was estimated to be 1.77% (y = - 0.043x2 + 0.152x + 0.593, P = 0.045) and 1.79 % A. vera (y = -2.778x2 + 9.95x + 29.29, P = 0.037), for growth and feed utilization respectively. Overall, A. vera extracts improved haemato-biochemical indices in A. vera supplemented fish when compared to unsupplemented ones, but decreased some of the indices at the 4.0% A. vera level. After blood sampling, fish were subjected to a low water pH (5.2 - 5.5) challenge and survival probability was measured. Fish fed diets supplemented with 1.0%, and 2.0% A. vera showed higher survival probability (above 70%) throughout the challenge period compared to the control (below 70%) and those fed the 4% A. vera supplemented diet (below 60%).