Survival performance in tilapia larvae undergoing sex reversal by consuming an immunomodulator

University of Sancti Spíritus “José Martí Pérez,” Yusbey Riera C., Ambar R. Reyes Companioni, The Pesquera Sancti Spíritus Company, Bulent Kukurtcu Targotay, Laboratorios Catalysis

Within the different stages of production of an ichthyic species, larviculture plays a vital role as the commercial success of a fish farm depends to a large extent on the controlled production of a sufficient number of fry (Lazo 2000; Atencio et al., 2003). In this sense, the survival of larvae remains a fundamental factor.

Despite advances in research to improve tilapia production, the management of high stocking densities unbalances and alters the organisms’ capacity to resist and adapt physiologically. This fact results in stress levels that are exploited by opportunistic pathogens, triggering diseases that cause economic losses (Jiménez, 2010). This is particularly evident in the sex reversal process when larvae become more susceptible to such problems.

In recent years, additives, probiotics and premixes have gained popularity, aimed at achieving better growth, higher survival and increased immunity (Monroy et al., 2012). In traditional Chinese medicine, licorice is called “the king of herbs” (Armanini et al., 2002; Cristina et al., 2008; Fiore et al., 2005) and it improves disease and stress resistance in fish (Chen et al., 1999, 2010a). The main component of Viusid Aqua, glycyrrhizinic acid, is obtained from its root.

Viusid Aqua is a nutritional supplement of natural origin, composed of antioxidants, vitamins and trace elements, which in recent years has been widely accepted in countries in both Asia and America with extensive aquaculture development (Catalysis, 2012). The current study represents the continuity of the research carried out in Cuba with this product in different aquatic species. Our objective was to evaluate the efficiency of the Viusid Aqua nutritional supplement (Table 1) containing immunomodulatory characteristics on the survival of tilapia larvae during sex reversal.

This research was carried out at the La Sierpe fish farm, the largest of its kind in Cuba, located on the banks of the Zaza dam, the largest reservoir in the country.

Eight concrete tanks with a total area of 200 m² were used for the test, four per treatment (T). In each treatment, 180,000 tilapia larvae (Oreochromis spp.) of a genetically improved variety were distributed in a completely randomized distribution design at a density

Table 1. Composition of Viusid Aqua® .

Malic acid Glucosamine Arginine Glycine Ascorbic acid (Vit. C) Monoammonium glycyrrhizinate

9.2 g Pyridoxine hydrochloride 9.2 g Zinc sulphate 8.3 g Calcium pantothenate 4.7 g Folic acid 2.3 g Cyanocobalamin 0.46 g 0.45 g 0.23 g 0.23 g 0.1 g 0.01 g

of 9,000 larvae/m3. For T1, liquid Viusid Aqua was consistently added to the feed at a rate of 2 ml/kg of feed for 21 days. No Viusid Aqua was added to T2.

The nutritional regime consisted of commercial feed containing 17-α-dimethyl-testosterone masculinizing hormone and 60% protein. It was distributed in four daily rations at 7:30 am, 10:00 am, 12:30 pm and 3:30 pm. Growth and survival control were carried out through weekly biometrics, sampling 10% of the population of each experimental unit according to the operating procedures for tilapia farming (POT, 2007). These biometrics were used to adjust the feeding rate.

The physical-chemical indicators of water quality and the natural food base were monitored daily in the morning and afternoon. The following variables were measured: average weight of larvae every six days and at the end of the test, survival rate, total feed consumption and total biomass of the harvest.

Table 2 shows weight differences between groups at the beginning of cultivation and no significant differences (p≤0.05) on the final weights. Therefore, we conclude that no direct influence was exerted by the product on this variable.

The average weights obtained in both treatments were appropriate as established criteria (POT, 2007). Density is considered to be of utmost importance, although this variable depends on several factors. Tetth-Doku et al. (2013), as well as Ferdous et al. (2014), only obtained a higher average final weight in treatments whose density was 1,000 fry/m3 (0.226 and 0.330 respectively), meaning a density below the one used by our study.

Table 2 show significant differences (p≤0.05) in biomass for T1 compared to the control, an effect primarily caused by the survival ratio using Viusid Aqua. Another positive aspect was the absence of feed consumption differences between the two experimental groups.

Table 3 shows significant differences (p≤0.05) in the survival rate in favor of Viusid Aqua. These results are consistent with those reported by various researchers on the effect of this product on survival (Ocampo, 2012; Ibarra & Casillas Hernández, 2013; Pulido, 2018). This behavior is attributable to the formulation of the product, which has been specially designed to help balance and stimulate the functions of the immune system, reinforcing the body’s immune system (Catalysis, 2012).

Table 2. Initial and final growth parameters of tilapia larvae (Oreochromis spp.) in the different treatments at the end of the sex reversal period.

Initial average weight (g) 0.0255 0.0240

End average weight (g)

0.2450 0.2200 End average biomass (kg/m3) 33.0475 27.4475 0.024* 0.067 ns 0.001*

Feed consumption (kg) 40.3865 39.0037 0.502 ns

* p≤0.05 ns = not significant 0.0005 0.0111 0.93 1.93

Table 3. Survival rate of the different treatments at the end of the sex reversal period.

T1 (Viusid Aqua) 74.9750 T2 (Control) 69.4250

* p≤0.05. 1.96702 2.17926 0.98351 1.08963

0.009**

The sex reversal process produces stress in the larvae and high mortality rates (Watanabe et al. 1977). Yet, population density remains an important factor associated with survival (Vera Cruz & Mair, 1993). When comparing our results with studies, we found that survival rates below 80% for sex reversal in different systems were also reported by Delarete et al. (2009), Borrovich (2010) and Phelps & Okoko (2011). Ramos (2017) obtained an 83.6% survival rate with a 6,000 larvae/m3 density. In our case, by using Viusid Aqua and a 9,000 larvae/m3 density, we achieved a 75% survival rate, classified as good as per the established criteria (POT, 2007). In contrast, the control group achieved a 69.4% survival rate.

Sex reversed tilapia that feed on Viusid Aqua showed higher productive performance and survival compared to the control treatment group.

References available on request

Professor University of Sancti Spíritus “José Martí Pérez”, Cuba E: vicente@uniss.edu.cu Contact: Bulent Kukurtcu, bulent@catalysis.es