Written by the Editorial Team of Aquaculture Magazine
One of the main challenges for the expansion of shrimp culture is securing the supply of balanced feeds, which in turn can represent more than 50% of the production costs. In this context, here are presented findings that contributes to a better understanding on the physiological effects produced during compensatory growth in shrimp, which in turn could assist in the development of improved feeding strategies in benefit of the aquaculture industry.
One of the main challenges for the expansion of shrimp culture is securing the supply of balanced feeds, which in turn can represent more than 50% of the production costs. In this regard, different strategies of feed management have been proposed to reduce the production costs, including the use of trays, variations on feed frequency, and temporary feed restriction.
Temporary feed restriction may promote an increased growth rate when optimal feeding conditions are restored (including de capod crustaceans); this biological response has been called compensatory growth. The compensatory response after refeeding is linked to the duration and severity of the previous feed restriction, and the length time of the refeeding period.
The promotion of compensatory growth to reduce operating costs during animal production is a well-documented strategy; nevertheless, there is still relevant information to disclose on the physiological effects occurring in the white shrimp Litopenaeus vannamei.
In this context, here is provided new insights on the physiological responses occurring during compensatory growth, by evaluating the metabolic turnover rate of nitrogen in muscle, by measuring the digestive enzyme activities and changes in the bacterial communities of the digestive tract of juvenile L. vannamei.
Materials and methods
Two experimental diets were formulated: (a) a pre-conditioning diet and (b) a reference diet. The pre-conditioning diet was manufactured with poultry by-product meal (55%) to promote a specific isotopic signature in shrimp before the feed restriction assay.
The reference diet was based on fish meal as main ingredient (56%) having a different isotopic signature for nitrogen. In this way, the dietary shift had the objective of promoting clear, exponential isotopic changes that eventually allowed estimating the metabolic turnover rate of nitrogen.
Shrimps were received at the Aquaculture Nutrition Laboratory at CIBNOR, and acclimated for 30 days in an 800-L fiber glass tank under controlled conditions.
Survival of shrimp during the experimental trial was higher than 90% for all treatments. After 7 and 14 days of the experimental period, shrimp under 70% feed restriction during 3 (T3) and 6 (T6) days showed significantly lower growth compared to the control group. On experimental day 35, shrimp under T3 treatment showed the highest final weight (3.47 ± 0.13g) compared to Control (3.38 ± 0.14g) and T6 (3.23 ± 0.04 g) treatments; nevertheless, no statistical differences were observed (Table 1).
Considering the shrimp growth between days 1 and 7, the specific growth rate (SGR) was significantly higher for shrimp in the Control treatment compared to feed-restricted shrimps. Nevertheless, during the recovery period without feed restrictions (from day 7 to 28), the SGR was significantly higher for T3 and T6 treatments compared to Control.
The digestive enzyme activities measured in the shrimp’s hepatopancreas are shown in Figure 1. The trypsin activity at day 9, during compensatory response, showed a significantly higher activity in shrimps belonging to T3 and T6, as compared to values observed in shrimp in the Control treatment (F2,11 = 9.24, p = 0.007). Nevertheless, after day 14, no significant differences were shown among treatments (p > 0.05).
In terms of bacterial digestive biota all replicate samples showed an average of 95,367 sequences as signed to 455 different OTUs. According to alpha-diversity in terms of Chao and Shannon indexes, the shrimp bacterial community in the digestive tract of shrimp were statistically similar (p > 0.05) among treatments and between sampling days (14 and 35) (Figure 2).
The compensatory growth is a mechanism that allows organisms to improve nutrient utilization and growth when food is abundant along natural fluctuations, including aquatic environments (Fraser et al., 2007; Buckup et al., 2008).
Results showed that shrimp under 3 and 6 days of 70% feed restriction showed compensatory growth with full recovery of growth after ad libitum feeding was restored. As in 40-day-old post larvae L. vannamei (116 ± 4 mg, avg. wt.) fasted for 3 days, full compensatory growth reached after 9 days of refeeding (Lin et al., 2008).
“On the other hand, determination of the SGR provides a valuable tool to identify specific periods of high growth rates (Ricker, 1975).”
In the study, shrimp showed a significantly higher SGR during the feeding recovery period, revealing a compensatory response, as observed in other studies conducted on the same species (Yu et al., 2008; Liu et al., 2022).
In the present work, treatments with feed restriction promoted between 5% and 12% feed saving as compared to Control shrimp. Furthermore, when natural food sources are available in the culture systems, as in biofloc systems, the feed saving could represent between 25% and 50%.
At the end of the experimental period, shrimp under all treatments approached isotopic equilibrium with values of δ15N = 14.31 ± 0.26‰, reflecting not only the fast growth, but also a high assimilation and utilization of nutrients supplied by the reference diet.
“Although the feed restrictions caused a significant reduction of the nitrogen turnover rates in muscle tissue, an isotopic equilibrium was still reached and it was mainly promoted by tissue accretion.”
Previous studies in crustacean and fish indicate that starvation can promote changes in the bacterial community structure with loss of bacterial diversity (Xia et al., 2014; Foysal et al., 2020; Sakyi et al., 2020).
In the showed results, at day 14 during compensatory growth, bacterial diversity was similar among treatments and few differences were found within taxonomic levels. It is possible that a partial feed restriction applied in short periods (3 and 6 days) might have a lower impact on the bacterial community structure in the shrimp gut, or that the period (at day 14) was long enough to reestablish the potential change of bacterial diversity lost during feed restriction.
Shrimp under 3 and 6 days of feed restriction achieved full compensatory growth, leading to up to 12% feed savings after 35 days of experiment. During the feeding recovery period, the nitrogen metabolic turn over rate was lower in shrimp under compensatory growth than in the Control group shrimps, reflecting an increased dietary nitrogen utilization destined for growth.
The bacterial community in shrimp gut was also modified during compensatory growth, with bacterial abundances pointing to potential benefits on nutrient metabolism and assimilation.
When full compensatory growth was achieved at the end of the experimental period, the evaluated parameters showed similar results as those determined in the Control treatment, suggesting a normalization of metabolism and the physiological state.
This is a summarized version developed by the editorial team of Aquaculture Magazine based on the review article titled “METABOLIC TURNOVER RATE, DIGESTIVE ENZYME ACTIVITIES, AND BACTERIAL COMMUNITIES IN THE WHITE SHRIMP LITOPENAEUS VANNAMEI UNDER COMPENSATORY GROWTH)” developed by: QUINTINO-RIVERA, J. – Centro de Investigaciones Biológicas del Noroeste (CIBNOR), ELIZONDO-GONZÁLEZ, R. – Conacyt CIBNOR, Gamboa-Delgado, J. – Universidad Autónoma de Nuevo León, GUZMÁN-VILLANUEVAM L., y PEÑA-RODRIGUEZ, A. – Conacyt– CIBNOR.
The original article was published, including tables and figures, on FEBRUARY, 2023, through PEELJ.
The full version can be accessed online through this DOI 10.7717/peerj.14747.