Institute of Hydrobiology, Jinan University, Key Laboratory of Aquatic Eutrophication and Control of Harmful Algal Blooms of Guangdong Higher Education Institutes, Guangzhou, China
Correspondence: X-T Lin, Institute of Hydrobiology, Jinan University, Key Laboratory of Aquatic Eutrophication and Control of Harmful Algal Blooms of Guangdong Higher Education Institutes, Guangzhou 510632, China. E-mail: firstname.lastname@example.org
This study assessed the effect of cyclical feeding on compensatory growth, nitrogen (N) and phosphorus (P) budgets of juvenile Litopenaeus vannamei. A 36-day growth trial was performed with four different feeding protocols. The control group (S0) was fed to satiation twice every day during the whole experimental period; treatment groups S1, S2 and S3 were fed by the 9, 5 and 3 cycles of 1:3, 2:5 and 3:9 (fasting days:feeding days) respectively. Fasting in S1, S2 and S3 groups did not change the specific growth rate in wet weight (SGRw), but the feed conversion efficiency (FCE) and protein efficiency ratio (PER) were significantly increased (P < 0.05) in comparison with control. The N and P consumed per unit wet weight gain of shrimp in S1, S2, S3 groups were significantly lower (P < 0.05) than control group by 15.39%, 15.96%, 19.33% for N, and 15.16%, 15.98%, 19.26% for P respectively. The total discharge of N and P (including N and P discharged by faeces (FN/P), non-faecal excretions (UN/P) and exuviations (EN/P); ) was significantly lower (P < 0.05) in the experiment groups by 19.91–22.07% for N and 18.68–26.37% for P respectively. Overall, the results suggest that the L. vannamei can reach completely compensatory growth, and the total discharge of N and P per unit wet weight gain of L. vannamei significantly decreased by cyclical feeding, which could have a positive effect on the reduced of environmental N and P loading due to the cultured of L. vannamei.
The total shrimp production in mainland of China accounts for nearly one-third of the world's total production of which 85% is contributed by Litopenaeus vannamei (Li & Xiang 2012). Commercial shrimp farming results in the discharge of a large amount of nutrients into waters in the form of suspended organic solids or dissolved matter such as carbon (C), nitrogen (N) and phosphorus (P), originating from surplus food, faeces and excretions via gills and kidneys (Tovar, Moreno, Mánuel-Vez & Garcı́a-Vargas 2000; Das, Khan & Das 2004). Shrimp feed accounts for 76–92% N and 70–91% P of the total inputs in the farm ponds, while only 23–31% N and 10–13% P can be assimilated by shrimp (Jackson, Preston, Thompson & Burford 2003; Thakur & Lin 2003). N and P are frequently considered the limiting nutrients to primary productivity in coastal and oceanic waters, and excessive levels of N and P in the aquaculture eventually leads to eutrophication even more to the harmful algal blooms of seacoast (Elser, Bracken, Cleland, Gruner, Harpole, Hillebrand, Ngai, Seabloom, Shurin & Smith 2007; Xu, Yin, He, Yuan, Ho & Harrison 2008; Xu, Yin, Ho, Lee, Anderson & Harrison 2009). Thus, one of the major challenges facing the shrimp farming industry is to reduce the discharge of N and P wastes to overcome environmental concerns.
Compensatory growth was defined as a physiological process whereby an organism accelerates its growth after a period of restricted development, usually due to reduced feed intake, in order to reach the weight of animals whose growth was never reduced (Hornick, Van Eenaeme, Gérard, Dufrasne & Istasse 2000). This phenomenon occurs in a wide range in aquatic animals such as crayfish (Cherax quadricarinatus), Atlantic halibut (Hippoglossus hippoglossus) and Chinese shrimp (Fenneropenaeus chinensis) (Wu & Dong 2001; Foss, Imsland, Vikingstad, Stefansson, Norberg, Pedersen, Sandvik & Roth 2009; Stumpf, Calvo, Pietrokovsky & Greco 2010), as well as in L. vannamei (Lin, Pan, Xu, Li & Li 2008). The mechanisms of compensatory growth are various such as the improvement in feed conversion efficiency (FCE) or the increase in food intake upon re-alimentation, or both of them were existed simultaneously at some species (Foss et al. 2009; Jiwyam 2010; Stumpf et al. 2010). Although the food intake increased during refeeding periods, the total intake of food throughout experiment is likely to decrease due to food deprivation in fasting period. Therefore, it is possible that reduced food intake and improved FCE of L. vannamei by intermittent feeding, could reduce the discharge of N and P originating from surplus feed, faeces and urine.
The current study selected L. vannamei as the subject of experiment to investigate the effect of cyclical feeding on compensatory growth, N and P budgets and the potential reduction for the loading of N and P in environment. These results may have beneficial effect for the further shrimp aquaculture.
Materials and methods
Experimental shrimp and facilities
The trial was conducted at the Maoming experimental station of Jinan University (Maoming Jinyang Tropical Fish Cultivation Co., Ltd), Guangdong Province of China. Litopenaeus vannamei (40 days of age) were procured from the same company and acclimatized in the running water aquarium system for 6 days prior to the experiment. The shrimp were fed to satisfaction twice daily (09:00 and 17:00 hours) with commercial feed (crude protein = 44.26%, crude fat = 7.76%) in acclimatized periods. The rate of water flow in each plastic tank (45 × 30 × 20 cm, water volume 24 L) was 600 mL min−1. The sea water for experiment was processed using precipitation and filtration methods. Water quality parameters, including dissolved oxygen contents (DO >5.0 mg L−1), salinity (26–28), pH (7.86–8.02) and water temperature (28–30°C) were monitored daily. The shrimp were subjected to indoor daylight lamp (illumination is 1200Lx ± 100Lx, and 12:12 photoperiod).
The experiment was conducted over 36 days, with one control group (S0) and three treatment groups (S1, S2 and S3) based on the cyclical feeding. Each group had four replicates with eight shrimp, so a total of 16 plastic tanks (45 × 30 × 20 cm, water volume 24 L) were included. The detailed implement design of the cyclical feeding in groups is presented in Table 1.
Table 1. Cycles of ‘Fasting and Feeding’ in experimental groups
Total feeding time (days)
The shrimp were fed continuously in S0 group throughout the experiment period. In the group S1, shrimp were fasted for a day followed by 3 days of feeding and this cycle (1:3) was repeated nine times. Shrimp in group S2 were fasted for 2 days followed by feeding for 5 days (2:5) with five repeats of the cycle, and one feeding day was added at the end of the fifth cycle. Shrimp in group S3 were fasted for 3 days followed by feeding for 9 days (3:9) with three repeats of the cycle. So a total of 27 feeding days and 9 fasting days were included in S1 and S3 group but 26 feeding days and 10 fasting days were included in S2 group (Table 1).
Total 128 shrimp (body weight: 0.50 ± 0.03 g) were selected after 1 day of food deprivation and randomly distributed into the 16 tanks with each tank holding eight individuals, and then four tanks were randomly allotted to each group. At the end of the experiment, all shrimp were fasted for a day, weighed individually and sampled for the analysis of body composition.
The shrimp in all experimental groups were separated each other by plastic nets to prevent cannibalism during the test. The nets were removed and the shrimp were fed to satisfaction twice daily (09:00 and 17:00 hours) with the same commercial feed (crude protein = 44.26%, crude fat = 7.76%, N% = 7.08% and P% = 1.94%) which used in acclimatized period during the feeding periods. Surplus feed was collected by syphon tube after 1.5 h feeding. Faeces were collected every 30 min by syphon tube until no apparent defecation was observed in 2 h. The nets were placed back to the tanks after surplus feed and faeces were collected. The total feed intake of shrimp was calculated by feeding quantity minus surplus feed, and then calibrated by the feed weight loss rate in water. The exuviations in each group were collected daily.
Growth and N, P budgets
The survival rate (SR, %), specific growth rate in wet weight (SGRw, % day−1), FCE and protein efficiency ratio (PER) were calculated as follows:
where Nt and Ni were the numbers of final and initial shrimp, Wt and Wi were the final and initial average wet weights (g) of shrimp, t was the total experimental time (days), C was the average dry weight of feed consumed (g) for shrimp and P was the average dry weight of protein consumed (g) for shrimp respectively.
The N or P intake (CN/P), growth in N or P (GN/P), discharged N or P from faeces (FN/P) or non-faecal excretions (UN/P) or exuviations (EN/P) and total discharge of N and P () per unit wet weight gain in shrimp were calculated as follows:
where PC was the N or P content of food, F was the mass of collected faeces and PF was the N or P content of faeces, Pt and Pi were the N or P content of shrimp on final and origin of experimental respectively, E was the mass of exuviations during experiment and PE was the N or P content of exuviations.
The dry weight of shrimp, surplus feed, faeces and exuviations were weighed after drying 24 h with 70°C in dry oven, and then stored at −20°C until analysed. Nitrogen contents of shrimp body, food, surplus food, faeces and exuviations were detected by Kjeltec™ 2300 (FOSS, Sweden), and phosphorus was detected using vanadium ammonium molybdate method (Galhardo & Masini 2000). The content of crude protein was calculated by 6.25 times of nitrogen content; and crude lipid was extracted by chloroform-methanol method (Wei, Zhong & Wang 2004).
The data were subjected to one-way anova and Tukey's multiple range analysis using spss 12.0. Results are presented as mean ± SD and differences were considered statistically significant at P < 0.05.
Growth and body composition
The SR of shrimp was 100% in all groups. The highest values of final weight (g) and SGRw (% day−1) were observed in S0 group, but no significant differences (P > 0.05) observed among groups throughout the experiment period (Table 2). Similarly, there were no significant differences (P > 0.05) observed in the contents of crude protein and crude lipid in shrimp bodies (%, wet weight) among groups (Table 2).
Table 2. Growth performance and body composition of Litopenaeus vannamei juveniles
Final weight (g, wet weight)
SGRw (% day−1)
Crude protein (%, wet weight)
Crude lipid (%, wet weight)
Superscript letters indicate statistical differences among groups; means not sharing a common letter are significantly different (one-way anova, P < 0.05).
2.22 ± 0.08a
4.13 ± 0.10a
16.55 ± 0.10a
1.27 ± 0.01a
2.15 ± 0.15a
4.04 ± 0.19a
17.69 ± 0.13a
1.42 ± 0.02a
2.08 ± 0.08a
3.95 ± 0.11a
16.49 ± 0.08a
1.21 ± 0.01a
2.18 ± 0.06a
4.08 ± 0.08a
16.47 ± 0.11a
1.20 ± 0.01a
However, FCE and PER in treatment groups (including groups S1, S2 and S3) were all significantly higher (P < 0.05) than that in control group (S0), but these values between groups S1, S2 and S3 were not statistically significantly (P > 0.05) observed (Fig. 1).
Table 3 showed the contents of N and P in bodies, faeces and exuviations of shrimp in groups, and no significant variation (P > 0.05) was observed among groups during the whole experiment period.
Table 3. The contents of N and P in bodies, faeces and exuviations of shrimp
N (%, dry weight)
P (%, dry weight)
Superscript letters indicate statistical differences among groups; means not sharing a common letter are significantly different (one-way anova, P < 0.05).
11.40 ± 0.09a
5.78 ± 0.12a
6.56 ± 0.05a
1.86 ± 0.12a
2.36 ± 0.14a
0.74 ± 0.01a
11.21 ± 0.11a
5.66 ± 0.34a
6.59 ± 0.10a
1.85 ± 0.11a
2.38 ± 0.18a
0.75 ± 0.01a
11.16 ± 0.12a
5.73 ± 0.26a
6.44 ± 0.08a
1.92 ± 0.16a
2.27 ± 0.22a
0.77 ± 0.04a
11.34 ± 0.13a
5.67 ± 0.39a
6.48 ± 0.06a
1.87 ± 0.08a
2.26 ± 0.15a
0.71 ± 0.06a
The mass of N and P in consumption and excretion
Figure 2 shows the N or P intake (CN/P), growth in N or P (GN/P), discharged N or P from faeces (FN/P) or non-faecal excretions (UN/P) or exuviations (EN/P) and total discharged of N and P () per unit wet weight gain in shrimp in the different experiment groups. The CN and CP in S1, S2, S3 groups were significantly lower (P < 0.05) than control group by 15.39%, 15.96%, 19.33% for N, and 15.16%, 15.98%, 19.26% for P respectively. The FN and FP also decreased significantly (P < 0.05) by 33.62%, 37.12%, 43.23% for N and 31.91%, 39.36%, 44.68% for P in S1, S2, and S3 groups compared with control group respectively. In addition, the UN and UP also significantly (P < 0.05) decreased in treatment groups, while the GN, GP, EN and EP were comparable in all groups.
The total discharge of N and P () per unit wet weight gain of shrimp in control group was 6.48 mg g−1 shrimp gain (about 72.81% N intake from feed) and 1.82 mg g−1 shrimp gain (about 74.59% P intake from feed) respectively, and those values in S1, S2 and S3 groups were 5.19, 5.44 and 5.05 mg g−1 shrimp gain for N and 1.48, 1.47 and 1.34 mg g−1 shrimp gain for P respectively, which significantly decreased (P < 0.05) by 19.91%, 16.05% and 22.07% for N and 18.68%, 19.23% and 26.37% for P respectively.
In the present study, the results showed that intermittent fasting did not affect the survival rate, crude protein and lipid contents in the L. vannamei. Moreover, similar levels of final weight and SGRw also showed that the feed restriction resulted in compensatory growth response in weight of juvenile L. vannamei in treatment groups (Table 2). These results corroborate with earlier studies which reported that a higher SGRw for L. vannamei upon re-alimentation after 4 days fasting (Yu, Lin, Xu & Zhou 2008). Similar results were also reported in Chinese shrimp, F. chinensis (Wu & Dong 2002), suggesting that the compensatory response happened after a short time of fasting in some shrimp species.
It was reported that L. vannamei can achieve complete growth compensation after a short time of food deprivation due to the significant increase in food intake upon re-alimentation (Lin et al. 2008), and a similar result was also observed in Chinese shrimp, F. chinensis (Wu & Dong 2001, 2002). In the present study, the FCE and PER of shrimp in feed-restricted groups were all significantly higher than that in control group (Fig. 1), suggesting that short-term fasting had a potential improvement on the digestion and absorption function of shrimp during refeeding periods, resulting in compensatory growth. Similar results were also observed in Atlantic halibut (H. hippoglossus) and sea bream (Sparus aurata), wherein greatest compensatory growth response was triggered by the dietary restriction (Foss et al. 2009; Bavcevic, Klanjscek, Karamarko, Anicic & Legovic 2010). Thus, the compensatory growth response of treatment groups in the present study was likely achieved by higher FCE and more PER in the periods of refeeding. Moreover, the previous research reported that the food intake was notably increased upon re-alimentation after 1–3 days food deprivation in L. vannamei (Lin et al. 2008), this may be one of the reasons which resulted in the compensatory growth of shrimp in the present study.
The feed deprivation in fasting periods led to notably reduced of N discharge by faeces compared with control group. In addition, the decrease of UN may be caused by the lower rate of protein hydrolysis in fasting periods. Many species of crustaceans including L. vannamei showed a biochemical adaptation response to a restricted of food by reduced enzyme activities and selectively using reserves just as hepatopancreatic glycogen and lipid for homoeostasis and to channel enough energy for basal metabolism in that period (Muhlia-Almazán & Garcıa-Carreno 2002; Comoglio, Gaxiola, Roque, Cuzon & Amin 2004; Zhang, Zhang, Li & Gao 2010). Protease activities decreased during food deprivation in F. chinensis, but an opposite response observed in amylase activities and lipase activities (Zhang et al. 2010). Those results were also supported by other research, which the trypsin and chymotrypsin activities of hepatopancreas significantly decreased after 120 h of fasting in the shrimp P. vannamei (Muhlia-Almazán & Garcıa-Carreno 2002), and similar phenomenon also existed in L. vannamei (Comoglio et al. 2004). According to these results, lipid and carbohydrate in the hepatopancreas are preferentially mobilized with protein-sparing effect at the food deprivation periods, and the decreased hydrolyzed rate of protein lead to the lower excretion of N in fasting periods, resulting in decreased total excretory N (non-faecal, UN) in the present study.
The shrimp had a low physiological need for dietary phosphorus and about 0.93% available phosphorus was adequate for its optimal growth (Cheng, Hu, Liu, Zheng & Qi 2006). Moreover, the absorption of inorganic phosphorus is much lower in shrimp, which ranged from 9.9% to 68.2% depending on the phosphorus sources (Davis & Arnold 1994). It is likely that the discharge of P in shrimp culture mainly originated from faeces and surplus food. In the present study, the food deprivation in fasting periods led to significant reduction in faeces and surplus food, which resulted in the decline of P discharge. However, the excretory P (non-faecal, UP) also significantly decreased in treatment groups, suggesting that the designed cyclical feeding had the potential to reduce the metabolism rate of phosphorus-containing compound in shrimp although the mechanism is not clear yet. Moreover, the lower food consumption and higher FCE in treatment groups can also reduce the faecal discharge, resulting in lower P discharge in treatment groups compared with control.
In conclusion, the cyclical feeding protocol in the present study could reduce the N and P intake (CN/P) but did not apparently affect the growth of L. vannamei. Furthermore, the discharge of N and P significantly reduced by 16.05–22.07% and 18.68–26.37% respectively in treatment groups, compared to 72.81% N and 74.59% P of the total inputs discharged to water in control group, which in agreement with the results of previous research (Jackson et al. 2003; Thakur & Lin 2003). The results suggested that using the cyclical feeding to trigger the compensatory growth in shrimp has a positive effect on reducing the N and P released into the waters as suspended organic solids (surplus food and faeces mainly) or excretions via gills and kidneys, but the production of shrimp was not apparently affected. Moreover, it also has a potential positive role in the protection of aquaculture environment. However, as the shrimp used for this study were of relatively small size, and it is likely for L. vannamei to have different physiological characteristics in different growth phases, thus further researches should be conducted using shrimp of larger size. They will provide more comprehensive and useful information for the commercial culture of shrimp.
The research was supported by the Natural Science Foundation of Guangdong Province (04010453).