ABSTRACT Silver perch (Bidyanus bidyanus, Mitchell) of 65 g average weight were reared at high de... more ABSTRACT Silver perch (Bidyanus bidyanus, Mitchell) of 65 g average weight were reared at high density under controlled conditions on diets containing 24.8% and 40.6% protein. Diets were fed at 2% or 4% of the fish biomass day−1. Both protein concentrations and feeding level of the diet influenced growth and proximate composition of the fish at the end of the 50-day growth trial. Energy requirement for maintenance for these fish was found to be 77 cal BW−0.8 and for each unit of energy retained 3.78 cal BW−0.8 needed to be supplied, and for each gram of protein retained per metabolic body weight 5.04 g were required. The results indicate that it is possible to obtain the same weight increment when feeding a 24.8% protein diet at a level of 4% body weight day−1 as compared with only 2% body weight day−1 of a 40.6% protein diet. This study indicates that the nutritional requirements for early grow-out are similar to those found in a previous study with juvenile silver perch and adds information concerning the required relationships between dietary amino acids. The results provide information required for further refinement of nutrition for this species.
Fish living in freshwater and seawater environments experience constant osmotic pressure between ... more Fish living in freshwater and seawater environments experience constant osmotic pressure between their internal body and the surrounding water. Regulation of ion and water balance under these conditions is highly energetic demanding, and eventually, affects the fish growth. While the role of the gills in osmoregulation was extensively studied, the osmoregulatory activity of the gastrointestinal tract is less known. In this study we characterized the tilapia intestine as a multifunctional organ, having a role in both nutrition and in ion regulation. We studied the pituitary endocrine regulation of intestinal salinity adaptation, the salinity-dependent physiological activity along different intestinal sections, and specific genes that are linking nutrient absorption with ion and acid-base regulation. The results of this study indicate that different intestinal sections developed various specific activities. Their endocrine regulation is now better understood, a large data-set of salinity dependent gene transcript was developed, as well as new tools and methods to study new aspects of intestinal physiology.
ABSTRACT In fish production under organic standards, only organic feeds and manures can be suppli... more ABSTRACT In fish production under organic standards, only organic feeds and manures can be supplied. The cost of organic pelleted feeds is twice that of regular feeds. To support the organic production of hybrid tilapia [Oreochromis niloticus (L.) ×Oreochromis aureus (Steindachner)], a series of experiments in earthen ponds, to improve natural food production for this fish while reducing costs of added feed, are in progress. To improve natural food production for tilapia, plastic substrates equivalent to 50% of the pond surface were introduced into the water column to induce periphyton growth on them. To reduce costs, the feeding rate on pelleted feed was reduced to 60%. Tilapia growth in these periphyton ponds was then compared with ponds without underwater substrates that received the full feed rate. The polyculture consisted of 90% large (320 g stocking weight) hybrid tilapia and small amounts of other fish, at a total stocking density of 13 800 fish ha−1, during 87 summer days. The results showed improved nitrification and the development of a large autotrophic periphyton biomass that competed with the phytoplankton in the periphyton ponds, and only a 10% and 15% reduction, respectively, in the tilapia daily and specific growth rates, with 40% feed saving. These results point towards periphyton-based aquaculture as an appropriate technology for the reduction in production costs, allowing economically viable organic tilapia production.
ABSTRACT Silver perch (Bidyanus bidyanus, Mitchell) of 65 g average weight were reared at high de... more ABSTRACT Silver perch (Bidyanus bidyanus, Mitchell) of 65 g average weight were reared at high density under controlled conditions on diets containing 24.8% and 40.6% protein. Diets were fed at 2% or 4% of the fish biomass day−1. Both protein concentrations and feeding level of the diet influenced growth and proximate composition of the fish at the end of the 50-day growth trial. Energy requirement for maintenance for these fish was found to be 77 cal BW−0.8 and for each unit of energy retained 3.78 cal BW−0.8 needed to be supplied, and for each gram of protein retained per metabolic body weight 5.04 g were required. The results indicate that it is possible to obtain the same weight increment when feeding a 24.8% protein diet at a level of 4% body weight day−1 as compared with only 2% body weight day−1 of a 40.6% protein diet. This study indicates that the nutritional requirements for early grow-out are similar to those found in a previous study with juvenile silver perch and adds information concerning the required relationships between dietary amino acids. The results provide information required for further refinement of nutrition for this species.
Fish living in freshwater and seawater environments experience constant osmotic pressure between ... more Fish living in freshwater and seawater environments experience constant osmotic pressure between their internal body and the surrounding water. Regulation of ion and water balance under these conditions is highly energetic demanding, and eventually, affects the fish growth. While the role of the gills in osmoregulation was extensively studied, the osmoregulatory activity of the gastrointestinal tract is less known. In this study we characterized the tilapia intestine as a multifunctional organ, having a role in both nutrition and in ion regulation. We studied the pituitary endocrine regulation of intestinal salinity adaptation, the salinity-dependent physiological activity along different intestinal sections, and specific genes that are linking nutrient absorption with ion and acid-base regulation. The results of this study indicate that different intestinal sections developed various specific activities. Their endocrine regulation is now better understood, a large data-set of salinity dependent gene transcript was developed, as well as new tools and methods to study new aspects of intestinal physiology.
ABSTRACT In fish production under organic standards, only organic feeds and manures can be suppli... more ABSTRACT In fish production under organic standards, only organic feeds and manures can be supplied. The cost of organic pelleted feeds is twice that of regular feeds. To support the organic production of hybrid tilapia [Oreochromis niloticus (L.) ×Oreochromis aureus (Steindachner)], a series of experiments in earthen ponds, to improve natural food production for this fish while reducing costs of added feed, are in progress. To improve natural food production for tilapia, plastic substrates equivalent to 50% of the pond surface were introduced into the water column to induce periphyton growth on them. To reduce costs, the feeding rate on pelleted feed was reduced to 60%. Tilapia growth in these periphyton ponds was then compared with ponds without underwater substrates that received the full feed rate. The polyculture consisted of 90% large (320 g stocking weight) hybrid tilapia and small amounts of other fish, at a total stocking density of 13 800 fish ha−1, during 87 summer days. The results showed improved nitrification and the development of a large autotrophic periphyton biomass that competed with the phytoplankton in the periphyton ponds, and only a 10% and 15% reduction, respectively, in the tilapia daily and specific growth rates, with 40% feed saving. These results point towards periphyton-based aquaculture as an appropriate technology for the reduction in production costs, allowing economically viable organic tilapia production.
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