As the estimated market demand for the Agulhas sole Austroglossus pectoralis exceeds the annual catch from trawlers, this species is a potential aquaculture candidate. Broodstock conditioning and gamete preservation is part of research and development aiming at establishing a breeding protocol for a new aquaculture species. Based on a literature review of the morphology of pleuronectiform spermatozoa, this study was designed firstly, to contribute to the field of spermatozoan morphology by describing the ultrastructure of A. pectoralis spermatozoa. This was followed by an experiment to cryopreserve mature spermatozoa to provide baseline data for future studies on this and related species. The testis of A. pectoralis was a paired structure encased in a membrane, the tunica albuginea. The primary testis was located on the dorsal surface of the rib cage and the secondary testis on the ventral side. The testis was of an unrestricted spermatogonial type, based upon observations of spermatogonia along the entire length of the lobule. Mature spermatozoa of A. pectoralis had an acrosome-free ovoid head 1.68 ± 1.6μm in length and 1.7 ± 1.6μm in diameter, a short mid-piece of 0.5 ± 0.1μm in length, containing 7 irregularly shaped mitochondria forming a ring-like structure at the base of the nucleus. The flagellae were 47.4 ± 4.8μm in length, most with two plasma membrane lateral fin-like projections. However, some flagellae had either zero or three lateral fin projections. Cross-sections of the flagellae showed an axenome with a 9+2 microtubule configuration. The proximal and distal centriols were coaxal, situated deep within the nuclear fossa. The structure of A. pectoralis spermatozoa conformed to the type 1 ect-aquasperm, also found in externally fertilizing species. This type has been suggested to be the plesiomorphic form in Neopterigians. Finally, this study contributed to a cryopreservation protocol for A. pectoralis spermatozoa by testing the two cryoprotectants dimethyl sulphoxide (DMSO) and glycerol. Glycerol, at a concentration of 10%, offered better cryoprotection than DMSO. This was established using flow cytometry analysis of post-thaw nuclear membrane integrity after 64 days of storage in liquid nitrogen. The toxicity of DMSO to isolated cellular proteins may have resulted in DMSO-treated sperm having the highest percent (35.2% ± 3.2%) of non-viable cells compared with 23.0% ± 2.5% and 27.8% ± 3.4% for glycerol and the control, respectively. The presence of sucrose in the Modified Mounib Medium extender solution may explain why 45.5% ± 5% of the sperm cells were potentially viable in the control treatment. Initially, the white margined sole Dagatichthys marginatus (Soleidae) was selected as the most suitable candidate for flatfish aquaculture in South Africa. Thus, the aim of this study was to investigate the cryogenic potential and ultrastructure of D. marginatus spermatozoa. However, due to a skewed sex ratio, there were not enough males available to study this species. A skewed sex ratio is common amongst soleids, thus, the need to develop effective cryopreservation methods and to develop an understanding of sperm morphology so that the best time for cryopreservation can be chosen. In conclusion, this first description of spermatozan morphology of A. pectoralis contributed to our understanding of soleid sperm ultrastructure. In addition, a comparison of testis appearance between fish sampled just prior to spawning season and fish with mature sperm provided information on the spawning season of this species. The findings from the cryopreservation experiment suggested that glycerol was a feasible cryoprotectant for this species when sperm was prepared under field conditions.

The major bottleneck during the domestication of the white-margined sole Dagetichthys marginatus in South Africa has been low larval survival. The cause of this is not clear but considering current literature on flatfish culture and more specifically soleid culture, nutritional deficiencies are hypothesized to be the main possible cause. Following the importance of nutrition, the first aim of the research was to use an ontogenetic developmental approach to develop a species specific larval feeding strategy. Ontogenetic development of D. marginatus showed that weaning will take place at much later ages than other soleids currently being farmed. This makes the partial replacement of Artemia with a suitable inert diet in co-feeding strategies very important to cut the cost associated of live food production. This leads on to the second aim, in which an 'in vitro' approach was used to model the digestibility of Artemia, which could ultimately contribute towards designing inert feeds with similar digestibility characteristics to Artemia in the future. Obtaining nutrients from food is closely linked to the functional status of the digestive tract, the support organs and the external morphological characteristics required for the ingestion of live or inert feeds. Considering both morphological and physiological ontogenetic development, it is clear that D. marginatus follow a similar pattern to other soleids. Larvae can successfully feed on Artemia as early as 3 days after hatching but exhibit a slow metamorphosis into the juvenile stage when compared to other soleids. The absence of any detectable acidic protease activity during the first 45 days of development and the importance of exogenous enzymes from Artemia all points to limited capacity to digest artificial diets. Prior to modelling the 'in vitro' digestion of Artemia, digestive enzyme activity at different pH's were modelled using functional forms from the normal distributive category of functions. / As there is no substantiated information for the general effects of pH on enzyme activity in the literature for finfish larvae, three species occurring in the same bio-geographical region of Dagetichthys marginatus, namely Sarpa salpa, Diplodus sargus capensis and Argyrosomus japonicus were used to investigate this effect. The fitted parameters, namely the optimal pH and sigma (the slope around the optimal pH) showed two interesting results. When using a negative log likelihood ratio test to test for differences between species for a particular enzyme, the optimal pH for alkaline proteases (7.67), lipase (8.03), amylase (7.69) and phosphatase (9.84) activity was the same for all three species. Furthermore, the study illustrated the potential to detect dietary shifts during ontogenetic development based on changes in enzyme activity around the optimal pH using the sigma parameter. Sarpa salpa showed increased amylase activity and a decrease in protease activity around the optimal pH with increased size, corresponding to a change in diet from zooplankton to algae. The 'in vitro' modelling approach taken in this study was based on known enzyme interactions and dynamics which makes the results very interpretable. from Artemia is achieved based on gut evacuation time and enzyme levels. This 'in vitro' study furthermore clearly indicates the importance of exogenous enzymes from Artemia, contributing as much as 54 percent to protein digestion and 64 – 72 percent to carbohydrate digestion. This was however, only an initial investigation, and further expansion of the model is required to achieve a complete understanding of Artemia digestion and ultimately partial replacement with artificial diets. A feeding strategy for D. marginatus should therefore follow those of other farmed soleids, although there will be a general delay in implementation due to slower development. Problems can thus be solved and improvements made by transferring technology from other soleids to D. marginatus.

The study of fish diets or feeding behavior is an important aspect in ecology. Analysis of fish stomach contents often provides data for determining resource utilization, feeding strategies, and overlaps in food items among and between species. Studies of fish diets could also be used for testing ecological theory or provide management procedures for fisheries if methods could be developed for minimizing competitive food utilizations by other fish and enhancing growth of exloited fish populations (Obrebski and Sibert 1977). In order to understand more about ecological communities and competitive predatory relationships of fish, more data are required on their diets and feeding habits (Pearcy and Hancock; 1973). Detailed accounts of prey items consumed by some flatfish in the northwest Pacific are by Hagerman (1952), Kravitz et al. (1977), and Pearcy and Hancock (1978). This study examines the diet and growth of two juvenile flatfish, the English sole, Parophrys vetulus (Girard 1854) , and the Speckled sanddab, Citharichthys stiamaeus (Jordan and Gilbert 1832). In the present study the English sole and Speckled sanddab are investigated in order to determine their growth and seasonal changes in their diets, switching of food items, and overlaps of diet items between species and among size groups within species.