ALBERT

Notes: Abstract. The satiation time, stomach capacity, gastric evacuation rate and return of appetite were investigated in Clarias gariepinus larvae. The evacuation of food from the stomach was described by the exponential model. Gastric evacution was found to be inversely related to return of appetite. Both satiation time and feed intake as a % of body weight were found to increase rapidly over the first few days of larval feeding, after which they remained constant. A simple model is proposed for the estimation of maximum feed intake in relation to feeding scheduled and feeding frequency for Clarias gariepinus larvae.

Notes: Abstract The timing of the onset of air breathing in young African catfish, Clarias gariepinus (Burchell) was investigated and demonstrated to vary as a power law function in relation to constant water temperatures between 20 and 35°C. In addition, the development of the accessory breathing organs on the second and fourth gill arches are examined and examples of scanning electron micrographs of the early developmental stages presented. The appearance of accessory breathing organs appears not to be prerequisite for the onset of air breathing and possible reasons for this are discussed. The value of the development of air breathing versus temperature relationship is considered in relation to hatchery management.

Notes: There is a difficult path to tread between strictly accurate scientific nomenclature, which definitively and clearly characterizes exact developmental stages, and the vernacular names popularly used in the fish culture industry. On the one hand, the recognition of early life stages by the culturist is important because the requirements of young fish change rapidly with age (e.g. Hogendoorn 1980; Verreth & Van Tongeren 1989). On the other hand, recognition of microscopic changes can be more subjective than definitive and may be of no actual benefit in fish culture. Working definitions of developmental stages for aquaculture are therefore most usefully practical ones. In response to calls for a clear definition regarding the length of the larval period, in order to enhance the compatibility of different studies (Verreth & Van Tongeren 1989), the following definitions for African catfish, Clarias gariepinus (Burchell) are suggested.

Notes: Abstract. The growth and survival of Clarias gariepinus (Burchell) fry was investigated at high stocking density. Significant increases in mean fry weight, and concomitant significant decreases in specific growth rate, were recorded over successive 5-day periods. Fry growth was negatively density dependent. Fry survival was in excess of 90% in all treatments. Increasing stocking density between 50 and 150 fish/l altered the pattern of mortality; non-cannibalistic deaths decreased significantly with increasing stocking density though cannibalism did not significantly increase. Periods of weaning fish onto larger feed particles were associated with temporarily increased rates of cannibalism.

Notes: Abstract. The relative merits of tilapiine fishes, especially Oreochromis niloticus (L.) and Clarias gariepinus Burchell, are compared with respect to their suitability for aquaculture in Africa. Reproductive, nutritional and production data are drawn where possible from work carried out under African conditions.In view of the fact that African aquaculture is insignificant in terms of worldwide production and in terms of local fish consumption it is suggested that a broader view of species choice might be adopted in relation to aquaculture projects.The African catfish, by virtue of its suitable reproductive strategy, its nutritional efficiency and its ability to breath atmospheric oxygen, clearly represents an excellent candidate for aquaculture in Africa.

Notes: Cycles of movement and feeding of African catfish, Clarias gariepinus (Burchell 1822) fingerlings (113.48 ± 1.87 mm total length) were studied using an infrared illumination and video recording system. The study was carried out over a 15-day period with a group of 40 fish held at 30 °C under a 12-h light:12-h dark photoperiod. The fish were nocturnal and took over 70% of their daily ration at night when given access to food 24 h a day. When feeding was restricted to the light phase, feeding activity decreased, but nocturnal feeding was restored from the second day after a return to 24-h food access.

Notes: Natural resource managers in Pakistan today preside over a massive investment in water distribution infrastructure. An historical bias towards large-scale irrigation systems and a focus on water use for arable crop production appears to have contributed to an imbalance in food production in the region. This has resulted in the diminished supply and elevated price of fish and meat products, compounded by the disruption of natural fisheries. The situation is inconsistent with the regions food security needs and an important potential role exists for increased aquaculture development.Physically and organizationally, the integration of various fish production approaches into existing land and water use practices would also appear to be fundamentally feasible. There would appear to be strong economic justification for diversified water use involving fish production, especially small and medium-scale carp production in ponds, using ground water. More broadly, within the context of the limited potential for further expansion of water resources, integrated aquaculture could contribute a vital productive element to various components of the water distribution arid irrigated farming systems in the Punjab. These include: supply canals, provided diverse institutional and engineering objectives can be accommodated; groundwater (including potential application of saline groundwater); the farm sub-system, especially integrated rice and fish production options in conjunction with alternative pest control strategies such as Integrated Pest Management; and irrigation drainage systems, where water quality permits.Therefore urgent broad research objectives should include the definition, investigation and development of a series of distinct economic and environmentally sustainable approaches to integrated animal protein production from aquatic resources, presently managed principally for agricultural production. Approaches should involve both the replacement of lost fishery potential resulting from large-scale irrigation development and flood control management, and the development of net gains in aquatic output, and should focus particularly on efforts to promote recycling of agricultural residues, reduced pesticide use and efforts to make better use of scarce water resources through the integrated aquaculture production across a broad range of water resources.An increasing number of countries are approaching full development of their surface water resources, and like Pakistan many face the development of new management approaches to increase diversity and improve productivity in relation to water use. The lack of research in support of the development of integrated aquaculture, which lags many years behind comparable agricultural research, may be constraining the breadth of choice available to natural resource managers to meet their food security needs.

Notes: Large variability between ponds in aquaculture experiments often leads to imprecise estimates of treatment effects. One solution would be to increase the number of experimental ponds but the availability of ponds is usually limited. A cross-over trial makes comparisons directly within the same pond, instead of across ponds, thus taking account of individual pond effects and potentially removing much of the variability. A cross-over trial was initiated to test the feasibility of using such designs in pond aquaculture research. When compared to a completely randomized design, the cross-over trial was more efficient for comparing the fish growth for each of the two treatments, and, on average, a considerable reduction in the standard error of the treatment estimate was achieved. Thus, under certain circumstances, the cross-over design has great potential to improve the precision of pond aquaculture experimentation.

Notes: Circular tanks are appropriate for Clarias gariepinus (Burchell) culture. Wide/shallow tanks (with a diameter to depth ration of about 10) are preferable to narrow/deeper tanks. The optimal flow rate for larvae will be one which provides sufficient oxygen yet does not generate a current velocity fast enough to cause them to swim against it. However, current velocity, for a given type and orientation of inflow, will depend particularly upon tank diameter to depth ratio and flow rate and will be related to position within the tank. Therefore for a given circular tank design a theoretical maximum flow rate and concomitant biomass can be estimated for a given mean fish size. Once airbreathing begins the optimal flow rate for fry is simply that which does not elicit swimming.

Notes: Abstract In order to promote the successful supply and satisfactory survival of African catfish, Clarias gariepinus (Burchell), it is advocated that the fish be reared in hatcheries until they begin air breathing. Research conducted over a number of years to develop culture technology for intensive hatchery rearing to the stage of air breathing is brought together here as an overview. In particular, the definition of early development stages is considered as well as induced spawning, egg incubation, larval rearing and fry rearing.