Dietary nucleotide supplementation of Pacific white shrimp farmed in intensive outdoor ponds

Romi Novriadi, Ph.D. Oriol Roigé Sergi Segarra, Ph.D.

Results in Indonesia showed better performance and profitability and significantly higher survival rates when challenged with Vibrio harveyi

nucleotides
Authors assessed the effect of the dietary supplementation of a commercial nucleotide on Pacific white shrimp cultured in intensive outdoor ponds in Indonesia. Results showed animals receiving nucleotide diets had better performance and profitability and significantly higher survival rates when challenged with Vibrio harveyi. Photo by Darryl Jory.

Over the past several years, awareness has arisen around the concept that the most sustainable strategy for enhancing Pacific white shrimp (Litopenaeus vannamei) growth performance and survival should rely on the development of functional diets that allow health and economic benefits beyond basic nutrition. There are several functional products available that could contribute to such aims, including growth promoters, probiotics, prebiotics, immunomodulators, phytogenic substances and organic acids to target intestinal health, stress and disease resistance of aquatic organisms.

Nucleotides are immunomodulatory compounds, the building blocks of DNA and RNA, and are important for many physiological processes in living organisms. In L. vannamei, the use of nucleotides has been studied and reported as they can be supplied through the feed and lead to enhanced disease resistance and growth performance during the culture period. Dietary nucleotide supplementation has also been proven to improve biological functions and to provide several health benefits in other animal species, including modulation of immunity, resistance to infection and enhancement of growth performance.

In penaeid shrimp, Vibrio harveyi is recognized as a serious cause of disease, contributing to mass mortality during the grow-out production system. From a biological perspective, supplementing diets with nucleotides seems especially adequate in the early stages, since rapid weight gain occurs during the juvenile stage. To develop sustainable and economically adequate practical diets for L. vannamei, and considering that in the near future a reduction in the use of fishmeal is expected to continue, nucleotides could be used in shrimp feed formulations to counteract the negative effects of other ingredients.

This article – summarized from the original publication (Novriadi, R. et al. 2022. Effects of Dietary Nucleotide Supplementation on Performance, Profitability and Disease Resistance of Litopenaeus vannamei Cultured in Indonesia under Intensive Outdoor Pond Conditions. Animals 2022, 12(16), 2036)  ̶  presents the results of research to evaluate the long-term effects of nucleotide supplementation on the performance, profitability, immune response, and resistance to V. harveyi of L. vannamei fed a diet in which fishmeal (FM) had been partially replaced with soybean meal (SBM) and cultured under intensive outdoor pond conditions in Indonesia.

Study setup

The growth trial was conducted in two, 20×30-meter commercial ponds at the Jakarta Technical University of Fisheries (Jakarta, Indonesia). A total of 22,500 L. vannamei were obtained from Salira teknik Benur (Serang, Banten, Indonesia) and acclimatized to the culture system for one week in the nursery tank. Shrimp (1.06 ± 0.01 grams initial mean weight) were then randomly distributed into 50 nets (450 shrimp per net) with a size of 2×2×1 meters. Ten replicate groups of shrimp were administered different types of experimental diets (4,500 shrimp per study group) using a nutrition research standard protocol for 110 days and fed by hand four times daily. Based on our historic results, feed inputs were pre-programmed assuming the normal growth of shrimp and feed conversion ratio of 1.5. Daily allowances of feed were adjusted based on the observed feed consumption, weekly shrimp counts and mortality.

Diets were prepared with different fishmeal inclusion levels and formulated with SBM, corn gluten meal and wheat products as the main protein ingredients. The control diet (10FM, containing 10 percent fishmeal) was designed to serve as a representative for commonly used diets for PWS production in the Indonesian market, as opposed to 6FM (6 percent fishmeal), which represented a diet in which fishmeal had been partially replaced with vegetable sources. Commercial nucleotides (N, Nucleoforce®, Bioiberica, S.A.U., Palafolls, Spain) were supplemented at 0.1 percent in diets containing different fishmeal levels: 10 percent (10FMN), 8 percent (8FMN) and 6 percent (6FMN). All diets were produced at the Karawang Aquaculture Development Center and manufactured using commercial methods with a twin-screw extruder (CXE 65 E, Jinan Shengrun, Jinan, China).

For detailed information on the experimental design, diet preparation of experimental diets and animal husbandry; growth and challenge trials; body composition analyses and other tests; and statistical analyses, refer to the original publication.

Vibrio harveyi, a significant pathogen of maricultured species

Results and discussion

Our results from this study indicate that the use of commercial nucleotides improved growth performance and profitability in L. vannamei and greater disease resistance. More specifically, in shrimp receiving diets in which fishmeal has been partially replaced with vegetable protein sources, nucleotide supplementation led to better final body weight (FBW), percentage weight gain (PWG), feed conversion ratio (FCR), average daily growth (ADG) and higher economic profits, as well as a healthier hepatopancreas and increased survival rates when challenged with V. harveyi. On the other hand, in L. vannamei receiving a commercial diet with regular fishmeal levels, nucleotide supplementation allowed higher disease resistance and no reduced performance, immune response and profitability, and without altering the organoleptic parameters.

The main positive impact of nucleotide supplementation in L. vannamei observed in this study is probably the improvement seen in growth performance. As the trend in reducing fishmeal usage continues, this beneficial effect would support the incorporation of nucleotides during L. vannamei production. Other authors have reported that the inclusion of 0.2 percent nucleotides produced significantly better specific growth rates (SGR) and feed conversion efficiency (FCE) in experimental animals compared to shrimp without dietary nucleotides after a 60-day feeding trial. In our previous study, despite not reaching statistical significance, the supplementation of 0.1 percent nucleotides led to better growth, especially in the group in which fishmeal had been partially replaced with soybean meal, compared to the control diet.

The role of nucleotides and metabolites in aquatic organisms has been studied now for over two decades, and the positive effects of various nucleotide products on growth and feed utilization performance in fish and crustaceans are well established. However, there are still very few reports explaining how nucleotides work or how they enhance the growth performance of L. vannamei. Some authors have previously argued that the feed attractant properties of nucleotides promote the rapid intake of the feed, which prevents the leaching of nutrients allowing the shrimp to benefit, especially by supporting growth performance, from the complete nutritional properties contained in the diet.

In our current study, we observed the effects of prolonged nucleotide administration on the growth of L. vannamei, up until they reached their market size. We noted that the 110-day administration period with intensive culturing in an open pond system provides a clear positive trend towards increased L. vannamei growth compared to the 70-day results obtained in our previous study.

Nucleotides modulate the immune response, and this could be seen with the improved results in the immune parameters evaluated during this trial. Unlike in previous experiments, here we did not see a significant effect in this regard. Nevertheless, the trends indicate that there was probably an effect that might have been significant if only restricted to the initial and more vulnerable stages of early shrimp development.

Supplementing aquaculture diets with nucleotides

Our data for whole-body proximate composition indicated a higher protein deposition in the groups receiving dietary nucleotides compared to the group without dietary nucleotides. In addition, we found comparable values for other nutritional profiles, including total fat, moisture content, carbohydrates and crude fiber content. The higher level of protein in the nucleotide-supplemented groups might be attributed to the ability of dietary nucleotides to influence protein biosynthesis by regulating the intracellular pool of nucleotides. This is closely related to the role of nucleotides as the building blocks for DNA, which is further transcribed and translated to form protein in the shrimp body.

We also observed that the inclusion of 0.1 percent nucleotides was capable of partially preventing the development of marked histological hepatopancreas alterations observed in the shrimp fed with 6 and 8 percent fishmeal. The benefits of adding nucleotides to the diet may be due to their low molecular weight, which favors optimum digestion and absorption processes in the hepatopancreas.

Reports on the organoleptic evaluation of shrimp fed with functional or alternative ingredients are scarce. We observed a better texture and sweeter flavor achieved with the inclusion of dietary nucleotides. Therefore, perhaps the use of nucleotides in diets might provide a positive influence on the sensory attributes of shrimp when fishmeal is reduced.

Profitability is a key parameter in shrimp production, and feed-associated costs constitute a major variable in shrimp production from an economic standpoint. Our results showed that, overall, nucleotides supplementation generates an increased return on investment to the farmer. More specifically, adding nucleotides to L. vannamei diets with reduced fishmeal leads to a higher gross margin thanks to the markedly improved performance, and despite the slight increased investment required initially. Furthermore, profitability in 10FMN is quite similar to that of 10FM, but 10FMN provides better disease resistance.

Further studies are warranted in order to further validate the effects of nucleotides in this animal species as well as to support the approach suggesting their ability to counteract the negative effects of replacing fishmeal with soybean meal in shrimp diets. This could be done in other countries with similar trends, like in Vietnam.

Perspectives

Results of our study demonstrated that dietary nucleotide supplementation in L. vannamei receiving diets in which fishmeal has been partially replaced with vegetable sources leads to improved growth performance, better disease resistance and greater profitability. In addition, the inclusion of nucleotides did not affect the organoleptic features of shrimp.

Based on the positive results attained in this study, the 0.1 percent dietary nucleotide supplementation could be considered as a complementary tool to enhance shrimp production cultured under intensive open-pond systems.

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