The influence of Aquahatch on the growth performance of larval and juvenile African catfish (Clarias gariepinus, Burchell 1822)

Joscelyne, Mark (2020-03)

Thesis (MScAgric)--Stellenbosch University, 2020.


ENGLISH ABSTRACT: Aquaculture is one of the fastest growing food production sectors in the world. However, the limited supply of quality seed stock is bottlenecking its growth. This is especially evident in the African catfish (Clarias gariepinus) subsector that is characterized by poor survival during the juvenile stage. During early development, fish are especially prone to nutrient deficiencies that affect development and overall growth. This study evaluated the potential of Aquahatch, a nutrient solution consisting of L-carnitine, B vitamins and nucleotides, to improve early development, yolk sac utilization and overall growth in African catfish. The product was administered once to the culture water at four inclusion levels, i.e. 0.0mL/L (control), 0.25mL/L, 0.5mL/L, and 1.5mL/L, and the duration of exposure was seven days. Three separate trials were conducted, with Trial 1 and Trial 3 conducted in a system of 100 L tanks, with a high but unknown number of African catfish larvae. Additional tanks were also allocated in Trial 1 that were absent of fish, to determine the stability/behaviour of the product in water over time. Trial 2 was carried out in a system consisting of 14L tanks, with 30 African catfish larvae allocated to each tank. Trials 1 and 3 were replicated nine times, and Trial 2 replicated four times. Trial 1 and 2 ran for seven days, both focussing on fish production performance during the treatment period. Fish parameters recorded during Trial 1 included larva body length, yolk sac dimensions (height, length and volume), yolk sac volume rate of change, body length:yolk sac volume ratio, and final individual fish weight at the end of the treatment period. The parameters analysed for Aquahatch behaviour in the culture water in Trial 1 include a comparison of treatment concentrations in tanks, with and without fish, as well as the change in concentration over time. Trial 2 reports on fish survival. Trial 3 ran for 104 days and focused on posttreatment growth performance which included individual weight and length, biomass, absolute growth rate, relative growth rate, specific growth rate, feed conversion ratio, mortalities, body condition, proximate analysis, haematocrit, cephalosomatic index and viscerosomatic index. In Trial 3, three different sampling methods, in combination with image analysis, were also evaluated as a tool for optimising data collection and fish wellbeing during sampling. In this study, no beneficial effects of Aquahatch, when supplemented in the culture water of early development African catfish, were found. Increasing Aquahatch inclusion resulted in a deterioration of water quality, as evident in the higher total ammonia nitrogen levels and decreased survival rate. An unfavourable short larvae body length was also observed with the 0.25mL/L inclusion level. The combination of the three sampling methods and image analysis used in Trial 3, proved to be of benefit during sampling. However, the image analysis procedure requires refinement to reduce analysis time. Observations that were not conclusive and require further investigation include a tendency for improved body condition, a decreased cephalosomatic index, and larger yolk sac volume and shorter body length during the period associated with the development of oral ingestion capabilities of the fish.


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