Feeding level and frequency for freshwater angelfish

The objective of this study was to determine the optimal feeding level and feeding frequency for the culture of freshwater angelfish (Pterophyllum scalare). A randomized block design in a factorial scheme (3 × 2) with three feeding levels (30, 60 and 90 g/kg of body weight (BW)/day) and two feeding frequencies (1x and 2x/day) was set up in duplicate, representing 24 experimental units. Data were analyzed using two-way ANOVA and the Tukey test for comparison between means. After 84 days, results indicated that both factors influenced fish performance. No interaction between these factors was, however, observed. Increased feeding level and feeding frequency resulted in increased feed intake. The feed conversion ratio was negatively affected by feeding level, but not affected by feeding frequency. Final weights were higher when fish were fed twice daily, at levels of 60 or 90 g/kg BW/day. Specific growth rate was higher when fish received 60 or 90 g/kg BW/day, regardless of the feeding frequency. Survival was not affected by any treatment, with mean survival rates higher than 90%. It is recommended that juveniles be fed at a level of 60 g/kg BW/day with a minimum of two meals per day, to attain optimal survival, growth and feed efficiency.


Introduction
Exports of ornamental fish have increased at a rate of 8% per year for the past ten years and world exports reached over U$312 million in 2010 (FAO, 2011).Freshwater angelfish (Pterophyllum scalare), an Amazon Basin cichlid, is regarded as one of the most beautiful and marketable ornamental fish (Chapman et al., 1997).
Compared with food fish, growth and nutrition of ornamental species has received little attention (Degani, 1993) and feeding of ornamental fish is based on extrapolations of nutrient requirements from food fish (Sales & Janssens, 2003).Few studies on nutritional requirements and diet for P. scalare are available (Degani, 1993;Ribeiro et al., 2007;Rodrigues & Fernandes, 2006;Zuanon et al., 2006;Norouzitallab et al., 2009) and none relates to feeding levels or feeding frequency for P. scalare.Feed represents over 50% of costs in aquaculture operations, so applying optimal feeding strategies can optimize profit (Lovell, 2002).
Feeding frequency is one of the most important factors for adequate feeding management.Insufficient frequency leads to poor growth and high mortality, especially in intensive systems.Conversely, increasing the frequency requires more labor and increases production costs (Carneiro & Mikos, 2005).Some studies (e.g.Thomassen & Fjaera, 1996;Lee et al., 2000;Carneiro & Mikos, 2005;Biswas et al., 2006;Flood et al., 2011) have proposed that the benefits of optimizing feeding frequency are insignificant.Other studies have found feeding frequency to be positively correlated to growth performance; thus more feeding per day results in greater benefits (Wang et al., 1998;Dwyer et al., 2002) Of all feeding practices, the feeding level is the most important variable influencing fish growth and feed conversion (Lovell, 2002).Feed unavailability leads to heterogeneity and mortality (Wang et al., 1998;Tesser & Sampaio, 2006) and overfeeding may lead to a negligible increase in growth rate (Tsevis et al., 1992;Thomassen & Fjaera, 1996) and a decrease in digestive efficiency (Fernandez et al., 1998), which has a detrimental effect on water quality (Johnston et al., 2003).
Obtaining optimum feeding frequency and level depends on factors that can also interact with each other, such as feed quality, developmental stage and culture system (Ruohonen et al., 1998;Lovell, 2002).The focus of the present study is to determine the optimal feeding levels and feeding frequency for juvenile freshwater angelfish.

Material and Methods
Juvenile freshwater angelfish were obtained from the Laboratory of Ornamental Fish (Sao Paulo State University -Aquaculture Center).They were acclimatized in a 500 L tank (at 27.0±0.1 ºC and pH 7.2±0.4)for one week prior to the start of the experiment, and fed a commercial diet containing 320 g of crude protein per kg.Fish were divided in two groups according to weight (0.7-1.2 g and 1.3-1.7 g) and randomly stocked (at a density of 15 fish per experimental unit) in 24 plastic tanks holding 60 L of water.Tanks were continuously aerated with an air stone, and cleaned prior to feeding sessions, to remove feces.After thirty minutes, each tank was siphoned, to remove residual feed, in order to calculate real feed intake.The siphoning of tanks did not affect fish feeding activity.
About 50% of the tank water was replaced daily and the most important water parameters (pH 7.9±0.7,pH meter YSI pH100; dissolved oxygen > 5.0 mg/L, DO meter YSI 55; and total ammonia < 0.3 mg/L, spectofotometry) were monitored every five days.In all treatments, the most important water parameters were within the normally range accepted and the water temperature was maintained at a level close to the thermal preference of this species (at 27.8±0.01ºC; Pérez et al., 2003).
Nutritional and energy composition analyses for feed ingredients were performed, prior to diet formulation, according to methods of the AOAC (2000) (Table 1).The experimental diet was formulated using available ingredients by the Least Cost method (Microsoft Excel 2003).Nutritional requirements were based on available data on crude protein requirements of Freshwater Angelfish (Zuanon et al., 2006;Ribeiro et al., 2007;Zuanon et al., 2009) and digestible energy of Nile Tilapia (Pezzato et al., 2002;Boscolo et al., 2002).
The ingredients were hand-mixed with 400 g/kg of hot water, pelletized at low temperature in a meat grinder and then oven-dried (60 ºC, 72 hours).Pellets were broken and standardized to a 0.7 mm diameter.
A randomized block design with two weight levels, in a factorial arrangement (3 × 2) was set up using three feeding levels and two feeding frequencies.Each unit was replicated, thus corresponding to 24 experimental units.Fish feeding frequencies were once (at 1700) and twice (at 0900 and 1700) per day.Feeding levels, of 30, 60 and 90 g/kg of body weight per day (BW/day), were distributed according to feeding frequency.Fish fed two times received 50% in the first and 50% in the second meal.Amounts were adjusted every two weeks, after weighing all the fish in each experimental unit individually.Before weighing, fish were subjected to a 24-hour fasting and handled with care using a saline solution of 4 g NaCl/L to prevent stress.

Results and Discussion
Interaction between frequency and level was not significant between the parameter evaluated (Table 2).Growth performance of juvenile fish was significantly affected by both treatments.Increasing the feeding level and the feeding frequency both resulted in increased feed intake (P<0.05).Feed conversion ratio was negatively affected by feeding level (P<0.05),but not by feeding frequency.Final weights were higher when fish were fed at 60 or 90 g/kg BW/day and twice a day (P<0.05).Specific growth rate was higher when fish received 60 or 90 g/kg BW/day (P<0.05),regardless of frequency.Survival was not affected by any treatment and the mean survival rate was higher than 90%.
The results of this study indicated that both factors influenced the performance of freshwater angelfish juveniles.No interaction between these factors was, however, observed at the levels that were tested.This species can be fed at 30 g/kg BW/day without developing nutritional disease or health problems.Nevertheless, the lowest final weight and specific growth rate obtained in this treatment indicates that this low feeding level is not suitable for growing out, regardless of whether feeding takes place once or twice per day.
Feed intake results suggest that the angelfish can consume more than 9 g/kg BW/day.Growth rate results indicate, however, that they will probably not grow any faster than the fish fed 60 g/kg BW/day.Fish growth rate is usually positively related to feeding level (Zuanon et al., 2004), reaching a maximum at the point of maximum feed intake (Tesser & Sampaio, 2006).From that point on, a growth plateau is reached and diets in excess of the maximum may lead to a decreased digestive efficiency, which has a detrimental effect on water quality (Johnston et al., 2003).The optimum feeding level depended on several aspects, such as developmental phase, culture system, water quality and feed quality.Zuanon et al. (2004), who conducted tests on blue gourami (Trichogaster trichopterus) at the same feeding levels as those used in the present study, concluded that fish fed at 90 g/kg BW/day showed the best growth performance.Tesser & Sampaio (2006), who tested feed levels from 40 to 200 g/kg BW/day, concluded that the optimum feeding level for Odontesthes argentinensis juveniles is 90 g/kg BW/day.Khan & Abidi (2010) suggest 58-69 g/kg BW/day to Heteropneustes fossilis fingerlings.
It is well known that feed efficiency is higher -with no significant reduction of growth rates -in fish that are fed at levels below satiation.Shimeno et al. (1997) found that carp fed at levels of 18.5 g/kg BW/day obtained similar weight gain, attained better feed efficiency, and had less fat accumulation than carp fed at satiation rate (23 g/kg BW/ day).Fernandez et al (1998) concluded that Sparus aurata had a better digestibility coefficient when fed at lower levels.Tesser & Sampaio (2006) obtained lower feed efficiency for pejerrrey Odontesthes argentinensis feeding at levels greater than 90 g/kg BW/day.Results from the present study concur with the above-mentioned findings, i.e., high consumption led to high FCR and lower feed efficiency.Only the FCR result obtained when fish were fed at 90 g/kg BW/day was very high when compared with that of other studies on the same species (Rodrigues & Fernandes, 2006;Zuanon et al., 2006;Ribeiro et al., 2007).This could be because the feeding level was not fixed and   ), survival (S), feed conversion ratio (FCR), specific growth rate (SGR) and feed intake (FI) of freshwater angelfish juveniles under three feeding levels and two feeding frequencies for 84 days fish were kept under various experimental conditions in terms of diet formulation, stocking density and water quality.
One feed per day is sufficient for some fish species, such as Cirrhinus mrigala and Labeo rohita (Biswas et al., 2006), Ramdhia quelen (Carneiro & Mikos, 2005) or Heteropneustes fossilis (Khan & Abidi, 2010).Two or more meals are, however, usually recommended for omnivorous fish (Pannevis & Earle, 1994;Wang et al., 1998;Dwyer et al., 2002).In the present study, feeding fish two times per day resulted in better performance compared with that attained when feeding once a day.This is consistent with findings of Fujimoto et al. (2002) who suggested that freshwater angelfish are omnivorous-carnivorous.During the experimental period, hierarchic behavior and fighting for the feed was observed among fish.Even though the competition did not lead to any significant mortality, feed disputes demand energy and this can be pronounced in fish that are fed once per day, in comparison with those fed twice daily.Social dominance hierarchies affect feeding behavior of fish fed in groups and this probably affects the optimal number of feeding sessions per day (Jobling, 1983).According to Wang et al. (1998), higher feeding frequencies may increase opportunities for subordinate fish to feed because dominant fish may become satiated and less aggressive, resulting in a reduction of inter-individual size variation.Feeding frequencies higher than those used in this study could possibly result in better performance, as only two levels of this factor were tested.

Conclusions
Juvenile freshwater angelfish should be fed at least two times per day at levels of 60 g/kg BW/day to ensure good survival, growth and feeding efficiency.

Table 2 -
P values, coefficient of variation (CV) and means ±SE for final weight (FW