Effect of Stocking Density and Rearing Facility on Growth and Profitability of Tilapia rendalli Fry
A study was conducted to compare the growth potential of Tilapia rendalli at three different stocking densities, using different rearing facilities. T. rendalli fry of 0.9±0.1g average weight were stocked in tanks and hapa-in-ponds at the stocking density of 30, 60 and 90 fry/m 3 . Locally made feed (CP-18%) was administered at 5% body weight three times a day for three months. Monthly sampling was conducted to assess growth by measuring weight and length for specific growth rate (SGR), average daily gain (ADG), weight gain (WG), and biomass (BM). The results of the study showed a significantly higher (P 0.05) as well as within the stocking densities (P > 0.05). The results of this study have a significant contribution towards stocking densities as well as rearing facilities used by hatchery operators. It is recommended that hapas mounted in pond fry rearing for T. rendalli fingerling production is most ideal. The results of the present study suggested that production of good quality fingerlings at stocking densities of 30 fry/m 3 must be adopted in the culture of T. rendalli as fish grows faster than the other stocking densities of 60 and 90 fry/m 3 as demonstrated in this study.
Some aspects of biology and aquaculture potentials of Tilapia guineensis (dumeril) in Nigeria
The paper emphasizes on the several attempts made to raise the brackish water tilapia species, Tilapia guineensis both on an experimental and production basis by researchers and fish farmers in Nigeria. Besides, the aquaculture potentials of Tilapia guineensis have been reported by several authors. However, problems exist which are not found with the culture of other tilapia species. Even under most favourable conditions (e.g. the monosex culture of Tilapia guineensis), a poor growth rate and a mediocre feed conversion do not presage profitable aquaculture exploitation. The present review therefore throws light on areas of further research to enhance the growth performance of Tilapia guineensis with emphasis on fish larvae nutrition and first feeding (development of bio-encapsulated feed for larval fish based on nutritionally enriched nematodes and Calanoid copepods), digestibibilty of the feed ingredients, elucidation of the dietary protein requirements, improved culture technique through the use of the Recirculating Aquaculture Systems and the adoption of the most recent technology (The YY Male technology) that produces Genetically Male Tilapia through genetic manipulation. Specific recommended areas for further research are also proffered.
The Effect of Feeding Frequency on Growth Performance and Feed Conversion Rate of Black Sea Trout (Salmo trutta labrax Pallas, 1811)
Growth and feed conversion are two critical variables determining the success in fish culture. Nutrition is one of the most important factors influencing the ability of cultured fish to exhibit its genetic potential for growth and reproduction. They are also greatly influenced by factors such as behaviour of fish, quality of feed, daily ratio size, feed intake or water temperature. Since the feed cost accounts approximately 40-60% of the operating costs in intensive culture systems (Anderson et al., 1997), the economic viability of the culture operation depends on the feed and feeding frequency. It means that nutritionally well-balanced diets and their adequate feeding are the main requirements for successful culture operations. Commercialized feed presented to cultured species is not only nutritionally well-balanced, but also readily ingested with minimum waste production and digested and converted to live weight in a predictable manner (Okumuş, 2000; Hasan, 2001). Each species has its particular food preferences and feeding behaviours. Feeding behaviour of fish is quite complex. Feeding and ingesting are the final result of a number of interacting factors between the fish (senses and hormonal systems) and its environment (stock density, size range or variability, season, day length, time of the day). In general, feed management or feeding techniques have two main objectives: i) to encourage rapid and positive consumption and thus reducing leaching of nutrients wastage; ii) to provide greater potential for growth by minimising the metabolic costs. The amount of the daily feed ratio, frequency and timing of the feedings and presentation of the predetermined ratio are the key factors of feed management strategies, influencing the growth and feed conversion (Jobling, 1995; De Silva and Anderson, 1995; Goddard, 1996). Thus these may be accepted as the major tools for materialising abovementioned objectives. Kaushik and Gomes (1988) observed that even under maintenance or zero growth conditions, frequent feeding reduced excretory losses of nitrogen, optimising the amount of nutrients and metabolic fuel made available for growth. Optimal feeding frequency may vary depending on species, age, size, environmental factors, husbandry, and feed quality (Goddard, 1996). Chiu (1989) summarised some of the experimental data available on feeding frequency at which optimal growth was observed in different fish species. The author noted the daily feeding frequency for rainbow trout fingerlings on 7.6-16.0 g. Piper et al. (1982) suggested three times daily feeding for 15.1-45.0 g rainbow trout fingerlings. The limited information available suggests that optimum feeding rates and frequencies should be determined for each species and different sizes of the same species cultured under various environmental and husbandry conditions. Black Sea trout is a new finfish species for intensive aquaculture (Tabak et al., 2001) and, the present study aimed at determining Abstract