Effect of Dietary Lipid on Growth, Feed Utilization, and Protein Sparing in Sooty Grunter, Hephaestus fuliginosus

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1 The Israeli Journal of Aquaculture - Bamidgeh 62(4), 2010, The IJA appears exclusively as a peerreviewed on-line Open Access journal at Sale of IJA papers is strictly forbidden. Effect of Dietary Lipid on Growth, Feed Utilization, and Protein Sparing in Sooty Grunter, Hephaestus fuliginosus L.P. Song 1 *, B. Han 2, A.Y. Wang 1, B. Hu 1, S.Q. Mao 1 1 Freshwater Fisheries Research Institute of Shandong Province, 3 Weili Zhuang, Jinan Shandong , China 2 Shanghai Ocean University, 999 Huchenghuan Road, Shanghai , China (Received , Accepted ) Key words: dietary lipid, protein-sparing, growth, sooty grunter Abstract The effects of dietary lipid on growth and feed utilization of sooty grunter juveniles (Hephaestus fuliginosus) were examined. Triplicate groups of 20 juveniles were fed diets containing 39% crude protein, supplemented with 0%, 3%, 6%, 9%, or 12% lipid (% dry matter) for 60 days. At the end of the experiment, at least 90% survived in all diet groups. Fish fed the diet containing 6% lipids had a significantly (p<0.05) higher growth rate and better feed conversion and protein efficiency ratios than the other groups. Muscle lipid contents increased dramatically as the dietary lipid level increased and the highest lipid content was obtained in fish fed the highest lipid diet. On the other hand, muscle protein contents declined as the dietary lipid level increased, and the lowest protein value was in fish fed the 12% lipid diet. Ash and dry matter contents did not significantly differ among groups. Increasing the lipid level to 6% was the most effective for improving fish growth and feed efficiency. * Corresponding author. Tel: , fax: , lpsyang1974@126.com

2 282 Song et al. Introduction Sooty grunter, Hephaestus fuliginosus, is a valuable tropical fish with few bones and good taste. Suitable water temperatures for the sooty grunter range C, and the optimal temperature is C. The sooty grunter efficiently utilizes commercial feed, grows rapidly, and is an increasingly important commercial species in China. Because of its fast growth, efficient feed conversion and high market value, aquaculture of the fish plays an important role in the economy of China. With the recent success of artificial propagation and larvae production, culture of the sooty grunter has attracted even more attention from the public and the scientific community. Despite the success of sooty grunter culture, the nutritional requirements for this important perch have not been thoroughly studied. Such information is essential to properly formulate diets that promote optimal growth at minimal cost. Dietary lipid provides a source of concentrated energy and essential fatty acids for carnivorous fish that are limited in their ability to utilize carbohydrates as an energy source (Sargent et al., 2002). The increased digestible energy content in fish diets due to lipid supplementation has a protein-sparing effect that reduces nitrogen losses to the environment (Cho and Bureau, 2001). On the other hand, excessive energy in diets can lead to decreased feed consumption, reducing the protein intake and nutrient utilization, and resulting in reduced growth (Ellis and Reigh, 1991). Moreover, high dietary lipid can affect carcass composition due to an increase in lipid deposition (Ogunji and Wirth, 2002). Therefore, dietary lipid levels should be carefully evaluated and balanced. Providing adequate energy from dietary lipids can minimize the use of higher-priced proteins as the energy source in fish diets (Ai et al., 2004; Hung et al., 2004). Thus, an adequate dietary lipid level is important for growth performance and product quality in fish (Tibbetts et al., 2005). We conducted this study to determine the effects of dietary lipid level on growth, feed utilization, and muscle composition in sooty grunter. Materials and Methods Diet formulation. Isonitrogenous diets with 39% protein were formulated to contain five different amounts of lipids: 0, 3%, 6%, 9%, or 12% (dry matter basis). The major dietary protein sources were freeze-dried white fish meal and soy meal (Table 1). Ingredients were weighed, blended in a Kitchen Aid mixer to produce a homogeneous mixture, pelleted in a commercial meat grinder, air-dried at room temperature, placed in sealed plastic bags, and stored at -20 C until use. All ingredients and chemicals were purchased from Shandong Tian Shen Feed Co., Ltd., Shandong, China. Mean total nitrogen was determined by the micro-kjeldahl method (AOAC, 1995), and crude protein was calculated as N 6.25%. Crude lipid was determined after organic extraction by chloroform-methanol (2:1 v/v). Ash was produced in a muffle furnace at 550 C for 7 h. The percentage of carbohydrates, including nitrogen free extracts (NFE) and crude fiber, was calculated by subtracting protein, lipid, and ash from 100% (Jobling, 2001).

3 Effects of dietary lipid in sooty grunter 283 Table 1. Formulation and chemical composition of lipid-supplemented diets for juvenile sooty grunter (Hephaestus fuliginosus). Ingredient (%) Diet (% supplementary lipid) Fishmeal (white fish) Soy meal Corn starch Cod liver oil (Norway) α-starch Vitamin mix* Mineral mix* Chemical composition (% dry weight) Crude protein Crude lipid Crude ash NFE + crude fiber * Lovell (1989, 1998) Stocking and feeding. Healthy juvenile sooty grunter were provided by the Fish Hatchery of the Freshwater Fisheries Research Institute of Shandong Province, Shandong, China. Before the experiment, fish were acclimated to laboratory conditions for 14 days during which they were fed a diet with no lipid supplementation. They were individually weighed and selected by health condition and body size (4.05±0.11 g; 3.86±0.13 cm). Chosen fish were unfed for 24 h before the growth study, then randomly allocated to net cages ( cm) held in a round cement tank at a stocking density of 20 fish per cage. Water temperature was maintained at 26±1 C and dissolved oxygen above 5 mg/l; one airstone in each cage provided aeration. Cages were kept in a natural photoperiod and all had similar light conditions. The cages were cleaned fortnightly. Diets were tested in triplicate groups. Fish were hand-fed the experimental diets to apparent satiation three times a day (08:30, 13:30, 17:30) for 60 days. The food pellets were distributed slowly, allowing all fish to eat without competition. Fish were bulk weighed and counted at the beginning and end of the experiment to the nearest 0.01 g and specific growth rate (SGR), feed conversion ratio (FCR), and protein efficiency ratio (PER) were calculated. Fish were unfed for one day before weighing. Chemical composition in fish muscles. At the end of the experiment, white muscles from 10 fish in each cage were excised and frozen at -20 C for analysis. After freeze-drying for 48 h, the muscle dry weights were obtained from triplicate samples of each dietary treatment. Crude protein, lipid, and ash contents of the muscles were determined as for the diets, and were converted to percentages of the total muscle by dry weight. Data analysis. Data from replicates are presented as means±se unless otherwise specified. Data were analyzed by one-way analysis of variance (ANOVA) for statistical significance. When differences were significant (p<0.05), Duncan's Multiple Range Test was used to rank the groups. All statistical analyses were performed using SPSS 17.0 for Windows.

4 284 Song et al. Results All fish adapted well to the experimental system, and no disease or water quality problems were observed. Survival ranged % and did not significantly differ among groups (Table 2). Final body weight, net weight gain, and SGR were significantly highest in fish fed the diet containing 6% lipid. FCR was highest in fish fed the 9% and 12% diets and lowest in fish fed the 6% diet. PER increased with increasing dietary lipid levels to 6%, then decreased with further increased dietary lipid. The 6% lipid groups had the best feed utilization (lowest FCR and highest PER), suggesting that feed efficiency was generally improved by increasing dietary lipid. Lipid contents increased in muscles from fish fed higher levels of lipid and was highest in fish fed the 12% diet. On the other hand, protein contents decreased as the lipid level increased and was lowest in fish fed the 12% diet. Ash and dry matter contents in all fish groups remained unchanged. Table 2. Weight gain, survival, feed utilization, and muscle composition (means±se; n = 3) of sooty grunter fed diets containing different percentages of lipid. Diet (% supplementary lipid) Initial body wt (g) 4.08± ± ± ± ±0.10 Final body wt (g) 7.06±0.23 bc 7.51±0.22 b 8.09±0.21 a 6.89±0.04 c 6.82±0.08 c Wt gain (g) 2.98±0.77 bc 3.52±1.01 b 4.04±0.53 a 2.78±0.61 c 2.78±0.80 c SGR ±0.05 c 0.88±0.06 ab 0.96±0.06 a 0.76±0.01 bc 0.68±0.05 c Survival (%) 93.33± ± ± ± ±1.61 FCR ±0.07 b 1.68±0.05 b 1.39±0.05 c 2.55±0.04 a 2.63±0.14 a PER ±0.05 c 1.57±0.05 b 1.89±0.06 a 1.03±0.03 d 1.00±0.05 d Muscle composition Dry matter (%) 22.40± ± ± ± ±0.63 Crude lipid (% DM) 11.05±0.15 c 11.36±0.06 c 12.59±0.04 b 13.42±0.32 b 15.36±0.12 a Crude protein (% DM) 83.64±0.09 a 82.66±0.03 ab 82.01±0.26 ab 81.79±0.13 b 80.63±0.09 b Crude ash (% DM) 5.13± ± ± ± ±0.05 Means in a row with different superscripts significantly differ (p<0.05). 1 Specific growth rate = [(lnwt 2 - lnwt 1)/(t 2 - t 1)] x 100, where Wt 2 = final wt, Wt 1 = initial wt, and t 2 - t 1 = no. days 2 Feed conversion ratio = dry wt of feed consumed/wet wt gain of fish 3 Protein efficiency ratio = [final body wt - initial body wt)]/protein consumed Discussion Fish gained increased weight when fed increased levels of dietary lipid up to 6%. However, fish fed more than 6% lipids in the 39% protein diet did not exhibit further increases in weight, SGR, or PER. High dietary lipid levels depress growth in some fish species (Pei et al., 2004; Du et al., 2005). This may be due to the limited ability of fish to digest and absorb high amounts of lipids, resulting in reduced feed intake, excess lipid accumulation in the liver

5 Effects of dietary lipid in sooty grunter 285 and other visceral organs, and dietary or metabolic imbalance (Luo et al., 2005). The increase in dietary lipid level was associated with an increase in diet energy. When fish are fed a diet containing excess energy, growth may be reduced due to reduced feed consumption. Other studies also show that an increase in dietary lipid level is associated with a decline in feed intake and growth (Ellis and Reigh, 1991; Lee et al. 2002). The FCR of the fish decreased as the lipid level increased, suggesting a significant effect of dietary lipid on diet utilization. In juvenile Asian seabass (growing from 80 to 210 g) fed with a diet containing 60.3% protein and 18% lipid, the FCR was 0.78 (Williams et al., 2003). Due to the protein-sparing effects of high lipid diets, dietary protein contents can be reduced by increasing the dietary lipid level without compromising growth (Sargent et al., 2002; Ai et al., 2004). However, high lipid diets can result in decreased body protein (Williams and Robinson, 1988). In our study, increased dietary lipid resulted in decreased protein contents in the fish muscle. Because protein retention is generally regulated by the non-protein energy input of a diet, PER is a better measurement of the protein-sparing effect of lipid (Lie et al., 1988). Despite the overall lower muscle protein contents, fish fed diets with a higher lipid content (up to 6%) resulted in a significantly higher PER. Although the protein-sparing effect is lacking in some circumstances (Thoman et al., 1999; Vergara et al., 1999), most studies suggest its occurrence (Peres and Oliva-Teles, 2002; Boujard et al., 2004). Our results also support the presence of a protein-sparing effect related to a higher level of dietary lipid. The correlation between dietary lipid and body lipid concentration is well documented and shows that excessive dietary lipid results in excessive fat deposition in the visceral cavity and tissues. Since high body-fat content in fish is unacceptable to consumers, increased body fat caused by high dietary lipid may reduce the commercial value of the fish. In conclusion, sooty grunter juveniles grew fastest with 6% dietary lipid in a 39% protein diet. Beyond this level, lipid supplementation resulted in accumulated muscle fat, decreased muscle protein, and less efficient feed and protein utilization. Based on these results, it is recommended to supplement 39% protein fish diets with 6% lipids. Acknowledgements The funding of this work was provided by the Department of Science and Technology of Shandong Province, Shandong, China. We acknowledge Ji Hua Shi, Guo Hong Ma, Yan Hua Zhang, and Xiao Ling Pang for their valuable help. We also wish to thank all other people involved in this study. References Ai Q., Mai K., Li H., Zhang C., Zhang L., Duan Q., Tan B., Xu W., Ma H., Zhang W. and Z. Liufu, Effects of dietary protein to energy ratios on

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