The sutchi catfish, Pangasius sutchi (Fowler 1937) was grown at 10 stocking densities in cages suspended in a river-fed channel during the summer of 2000. Catfish fingerlings (mean length 9.1–9.7 cm and mean weight 5.9–6.7 g) were stocked at densities of 60, 70, 80, 90, 100, 110, 120, 130, 140 and 150 fish m−3. After 150 days, growth and yield parameters were studied and a simple economic analysis was carried out to calculate profitability. The mean gross yield ranged from 15.6±0.27 to 34.5±0.44 kg m−3 and the net yield ranged from 15.2±0.22 to 33.5±0.36 kg m−3 and showed significant variations (P<0.05). The mean weights of fish at harvest were inversely related to stocking density. Both gross and net yields were significantly different and were directly influenced by stocking density but the specific growth rate, survival rate and feed conversion rate were unaffected. Higher stocking density resulted in higher yield per unit of production cost and lower cost per unit of yield. The net revenue increased positively with increasing stocking density. A density of 150 fish m−3 produced the best production and farm economics among the densities tested in this experiment.

Cage culture of sutchi catfish, Pangasius sutchi (Fowler 1937): effects of stocking density on growth, survival, yield and farm profitability

Can dietary lipid source circadian alternation improve omega-3 deposition in rainbow trout?

Effect of mixed feeding schedules with varying dietary crude protein levels on the growth and feed utilization of Clarias gariepinus (Burchell, 1822) fingerlings.

The optimal frequency for feeding ornamental fish species has yet to be clearly defined and this has led to uncertainty in the feeding routines used by many aquarists. Both overand underfeeding can be detrimental to the health of the fish and may cause a marked deterioration in water quality, reduced weight, poor food utilization, and increased susceptibility to infection. Consequently, specific growth rates and the efficiency of feed conversion can be directly related to feed ration and frequency. Therefore, it is important to be able to predict the most favorable feeding frequency relative to the species and size of fish. Although it is often postulated that feeding ornamental fish little and often throughout the day will result in more efficient feed utilization, research has not yet been conducted to validate this hypothesis. Published literature on frequency of feeding ornamental fish is limited when compared with that available from cultured fish species. Data from aquaculture research is commonly extrapolated and applied to ornamental species, which often proves to be unsatisfactory because of the differences in fish species and variation in diet formulations. In addition, the majority of research has focused on feeding fish to satiation, measuring the food intake, and linking this to growth performance and utilization. Research conducted with the ornamental Red Swordtail (Xiphophorus helleri) indicated that feeding 2 meals/d (where a meal is defined as providing food until fish stop eating [the point of satiation]) resulted in the greatest growth and reproductive success of this species in a cultured system, when compared with 4 alternative feeding regimens (1 meal in 3 d, 1 meal in 2 d, 1 meal/d, and 2 meals/d) (1). Further investigations by the same researchers using the Siamese Fighting Fish (Betta splendens. Regan) showed that 2 meals/d fed to satiation elicited maximum growth and reproductive output for this ornamental fish species when compared with 1 meal in 3 d, 1 meal in 2 d, 1 meal/d, and 3 meals/d (2). Additional research on commercially cultured fish species such as the Black Rockfish (Sebastes schlegeli) suggested that feeding to satiation once a day resulted in optimum growth and food utilization when compared with 1 meal every 2 d or 2 meals/d (3). In addition, juvenile Atlantic Halibut (Hippoglossus hippoglossus) displayed improved growth rates when fed to satiation 5 times/d, compared with 1/d (4), and African Catfish (Clarias gariepinus) exhibited greater growth rates when fed to satiation twice compared with 3 times/d (5). In one study where a set amount of food was offered, Giberson and Litvak (6) established that Shortnose Sturgeon (Acipenser brevirostrum) grew significantly better when offered a food ration of 3% of the tank biomass divided into 4 or 8 feedings/d compared to one. However, in the same study, growth and feeding efficiencies of Atlantic Sturgeon (Acipenser oxyrinchus) were unaffected by the frequency of feeding. Currently there appear to be no data available that directly relates feeding frequency to growth and efficiency of food utilization in the Common Goldfish (Carassius auratus). However, the closely related subspecies, Gibel Carp (Carassius auratus gibelio), exhibited significant increases in growth rate and feed efficiency when feeding frequency increased from 2 to 3, 4, 12, and 24 feedings/d, with the authors recommending an optimal feeding frequency of 24 meals/d for this species (7). However, fish were juvenile and fed to satiation, confirming that feeding frequency in part is a function of fish size, with larval and juvenile fish needing to eat more frequently because of their high energy demands. This current study aimed to assess the effects of feeding a set amount of food at a variety of meal frequencies on growth parameters of the Common Goldfish (Carassius auratus) and to identify the optimum number of feeds/d to maximize utilization of the food ration. 1 Published in a supplement to The Journal of Nutrition. Presented as part of The WALTHAM International Nutritional Sciences Symposium: Innovations in Companion Animal Nutrition, held in Washington, DC, September 15–18, 2005. This conference was supported by The WALTHAM Centre for Pet Nutrition and organized in collaboration with the University of California, Davis, and Cornell University. This publication was supported by The WALTHAM Centre for Pet Nutrition. Guest editors for this symposium were D’Ann Finley, Francis A. Kallfelz, James G. Morris, and Quinton R. Rogers. Guest editor disclosure: expenses for the editors to travel to the symposium and honoraria were paid by The WALTHAM Centre for Pet Nutrition. 2 Author disclosure: no relationships to disclose. 3 To whom correspondence should be addressed. E-mail: abigail.stevenson@ eu.effem.com.

The Influence of Feeding Frequency on Growth and Body Condition of the Common Goldfish (Carassius auratus)

A trial was conducted to determine the dietary protein requirement for growth of juvenile striped catfish (Pangasianodon hypophthalmus). Iso-energetic semi-purified diets (~ 19.78 MJ kg−1) with six levels of protein 20% (T1), 25% (T2), 30% (T3), 35% (T4), 40% (T5), and 45% (T6) were fed to triplicate groups of fish (initial mean weight 4.27 to 4.57 g) to satiation twice daily for 60 days. Growth, feed conversion, protein utilization, intestinal digestive enzyme activities, and body composition were measured as response variables. Best growth (P < 0.05) was observed in fish fed with 40% dietary protein, and second order polynomial regression analysis (y = − 0.0011x2 + 0.0816x + 0.0642; R
 2 = 0.9241; dietary protein levels as independent variable and specific growth rate as dependent variable) gave a protein requirement for growth of 37.1%. A minimum feed conversion ratio (FCR = 1.38) was found in fish fed with 35% dietary protein. Apparent net protein utilization (ANPU) was found to decrease (from 39.57 to 16.15%), with increasing dietary protein levels (P   0.05) was found to be independent of dietary protein levels. Whole body carcass composition (except ether extract) varied with the dietary protein level, and significant higher values of moisture content (72.31%), crude protein (18.83%), and ash content (4.33%) were observed in the treatment group fed with 40% dietary protein. Hence, it may be concluded that the dietary protein requirement for growth of P. hypophthalmus juveniles is 37.1%.

Protein requirement of juvenile striped catfish, Pangasianodon hypophthalmus

A 6-month feeding trial was conducted in field condition using 10 farm ponds (400–600 m2) to investigate the effect of mixed feeding schedules on the growth of sutchi catfish, Pangasius hypophthalmus with silver carp, Hypophthalmichthys molitrix. Fish were stocked at a ratio of 80:20 (sutchi catfish, 4.9±0.5 g: silver carp, 12.0±0.8 g) at the total rate of 25 000 ha−1. Two diets of high protein (30%, HP) and low protein (16%, LP) were prepared using locally available feed ingredients. Five different feeding schedules of high-protein diet continuously (HP), low-protein diet continuously (LP), 1-day low–protein/1-day high-protein diet (1LP/1HP), 7 days low–protein/7 days high-protein diet (7LP/7HP) and 14 days low–protein/14 days high-protein diet (14LP/14HP) were tested. The fish were fed twice daily at the rate of 15%, 10%, 8% and 5% of their body weight for first, second, third month and rest of experimental period respectively. Feeding rate was calculated only on the basis of sutchi catfish weight only and was adjusted every 2 weeks according to weight gain. Fish fed LP and HP on alternate day (1LP/1HP) resulted in significantly (P 0.05) between the growth rates and production of fish fed HP regularly and fish fed 7 days LP followed by 7 days HP (7LP/7HP). Fish maintained on LP grew the least. The feed conversion ratio (FCR) values for sutchi catfish ranged between 2.04 and 2.79 with feeding schedule 1LP/1HP showing the best FCR. The total production of fish (including silver carp) ranged between 8310 and 12 422 kg ha−1 6 months−1 with 1LP/1HP feeding schedule resulting in the highest production and net profit. The study demonstrated that feeding fish continuously with HP is less economical. Thus, for profitable sutchi catfish culture with silver carp, farmers can use the mixed feeding schedule of alternate day feeding of LP and HP as a means of reducing feed costs.

Effect of mixed feeding schedules with varying dietary protein levels on the growth of sutchi catfish, Pangasius hypophthalmus (Sauvage) with silver carp, Hypophthalmichthys molitrix (Valenciennes) in ponds

Abdul Mazid

Papers

Effect of mixed feeding schedules with varying dietary protein levels on the growth of sutchi catfish, Pangasius hypophthalmus (Sauvage) with silver carp, Hypophthalmichthys molitrix (Valenciennes) in ponds