Thesis (MSc)--Stellenbosch University, 2015. / ENGLISH ABSTRACT: Aquaculture is one of the fastest growing food producing sectors in the world. Over the past few years, aquaculture research has focused on improving rearing protocols and standards for the culture of aquatic organisms. Probiotics are gaining increasing interest as an alternative to antibiotics to improve animal health and welfare. The effects of probiotics on the physiological and biochemical development of the digestive tract of commercially raised Argyrosomus japonicus (dusky kob) larvae were investigated. Two probiotic treatments were compared to a control where the standard rearing protocol was applied. The growth of the larvae and histological development of the digestive tract was studied. The specific enzyme activity of key digestive enzymes was determined. Amylase, trypsin, pepsin, alkaline phosphatase, aminopeptidase N and leucine-alanine peptidase were assayed. The mean growth of the control group of larvae differs from the CSIR and BactoSafe treatment groups (P = <0.001). There were no differences in the histological development between the control and two treatments. The histology did indicate a slight delay in development of the digestive tract when compared to previous studies on dusky kob. No significant differences were observed between the control and treatment groups for any of the enzyme assays. The effect of probiotics on the development of the digestive system of dusky kob larvae could not be definitively described as it was not determined to what extent the probiotics had established in the gut. What the study did conclude was that the enzyme assays need to be refined in order to determine the optimal reaction conditions required for the determination of specific enzyme activity in commercially raised dusky kob. / AFRIKAANSE OPSOMMING: Akwakultuur is een van die vinnigste groeiende voedsel produserende sektore in die wêreld. Oor die laaste aantal jare het akwakultuur navorsing gefokus op die verbetering van grootmaak protokolle en standaarde vir die cultuur van akwatise organismes So het die belangstelling in pro-biotika, as alternatief tot antibiotika ten einde die gesondheid en welsyn van diere te verhoog, vermeerder. Die effekte van pro-biotika op die fisiologies en biochemiese ontwikkeling van die spysverteringskanaal van kommersieel geproduseer Argyrosomus japonicus larwes was ondersoek. Twee probiotiese behandelings is vergelyk met ʼn kontrole (standaard grootmaak protokol). Die groei van die larwes en die histologiese ontwikkeling van die spysverteringskanaal is ondersoek. Die spesifieke ensiem aktiwiteite van die sleutel verteringsensieme was ook bepaal. Amilase, tripsien, pepsien, alkaliese fosfatase, aminopeptidase N en leusien-alanien peptidase was ondersoek. Die gemiddelde groei van die kontrole groep was effe hoër as die van die ander twee behandelings. Daar was geen verskil in histologie van die groepe nie maar die tempo van ontwikkeling vir alle behandelinge blyk stadiger te wees as die wat in vorige studies vir A. japonicus rapporteer is. Geen betekenisvolle verskille is opgemerk tussen die kontrole en die behandelingsgroepe vir enige van die ensiem analises nie. Die invloed van die probiotika op die ontwikkeling van die spysverteringskanaal van die larwes kon nie onomwonde beskryf word nie aangesien die vestiging van die pro-biotika in die spysverteringkanaal nie omskryf is nie. Wat wel gevind was, is dat die analitiese tegnieke rakende die ensieme verfyn moet word ten einde die optimale reaksie omgewings te bepaal wat dit sal moontlik maak om spesifieke ensiemaktiwiteite in die kommersieel geproduseerde A. japonicus te bepaal.

>Magister Scientiae - MSc / Aquaculture is a vast industry all over the world and has increased significantly during the past 30 years. In South Africa, finfish aquaculture farms stretch from Gansbaai to as far as Richards bay with the potential of extending into Mozambique. The future success of this fast growing industry in South Africa strongly relies on the development of the supporting sector such as government legislation, sponsorship, participation of the pharmaceutical industry and research and development in aquatic organism health management. Diplectanum oliveri Williams, 1989, a monogenean gill parasite of both Argyrosomus japonicus (Temminck & Schlegel, 1843) (dusky kob) and A. inodorus Griffiths & Heemstra, 1995 (silver kob) is currently regarded in South Africa as the most persistent ectoparasite associated with the culture of both fish species, causing pathological tissue changes in the areas associated with attachment and feeding which can result in stock losses. The egg production of D. oliveri was used to evaluate and develop a method to quantify monogenean infections on fish, by counting the eggs produced by infra-populations of these parasites over a 24-hour period and to determine the reliability of this method as a non-invasive/non-destructive method to quantify the intensity of an individual infra-population of parasites on a single host. Currently, Diplectanum spp. on dusky kob are being controlled in local mariculture facilities using methods and drugs that are traditionally used for monogeneans (flukes) and are regarded as effective. Most of these drugs are, however, no longer approved for use in food fish and none of them has proven to be very effective in controlling D. oliveri in culture facilities, which can result in subsequent re-infections of epidemic proportion. Currently, there are no anthelmintics registered for aquaculture in South Africa. An registered anthelmintic used in terrestrial animals (sheep, goats, cattle and ostriches) containing praziquantel was tested at various concentrations and exposures against D. oliveri on A. japonicus to determine the efficacy of two different formulations and the potential for "off label" use. The 20 ppm (high) praziquantel concentration treatments eliminated all adult parasites, but caused significant measureable stress and affected the central nervous system of the fish, which resulted in death of all fish in the solution group after 18 hours. The 2 ppm (low) concentrations failed to remove all adult parasites. Although both the 2 hour (short) exposure/high concentration and 24 hour (long) exposure/low concentration of the suspension formulation were effective, but only the short exposure/high concentration eliminated all adult parasites with little change in behaviour by the treated fish.