Impacts of different methods on water quality management on growth performance and quality of tilapia intensively cultured in earthen ponds

Phan Phuong Loan, N T T Hang¹ and N L Tuyen²

Agricultural and Natural Resources Faculty, An Giang University, Vietnam National University Ho Chi Minh City, Vietnam
pploan@agu.edu.vn
¹ Agricultural and Natural Resources Faculty, An Giang University, Vietnam National University Ho Chi Minh City, Vietnam
² An Giang University, Vietnam National University Ho Chi Minh City, Vietnam

Abstract

The aim of this study was to assess the impact of different methods of water quality management on water quality, growth performance, feed utilization and quality of monosex GIFT strain of tilapia. A field trial was conducted for 90 days in which tilapia fingerlings (3.19±0,89 g) were randomly distributed into three replicate ponds which were subdivided into three treatment groups, including: CTL = no water exchange, no aeration, and no probiotic application; WX = water exchange, no aeration and no probiotic application; and WXAP = no water exchange, aeration and probiotic application. The results showed an improvement of water quality in term of dissolved oxygen and ammonia concentration of WX and WXAP ponds compared to CTL ones. Growth performance (final weight, daily weight gain and specific growth rate) and survival ratio of the fish in WXAP ponds was highest and significantly different from the others. Feed conversion ratio of the fish of WXAP and WX treatments was better than CTL one (1.73, 1.80 and 1.89, respectively). The harvested fish from the WXAP ponds was more even in weight, and from the WX and WXAP ponds was low in off-flavor intensity compared to the rest. This study clearly demonstrated that the combination of aeration and probiotic supplement in water is the advanced method for tilapia production with high quality in intensive ponds over the tradition method of water exchange.

Keywords: earthen pond, feed utilization, growth performance, off-flavor, tilapia intensive culture, water quality

Introduction

Tilapia is the common name of a group of fish species originated in Africa but now worldwide cultured, particularly in Asia and the Pacific (De Silva et al 2004). All tilapia species with important commercial values farming outside Africa belong to Oreochromis genus and more than 90% is Nile tilapia (Oreochromis niloticus) (Popma and Masser 1999; Watanabe et al 2002). In 2018, tilapias were the second species of cultured food-fish, after carps, with a production of 4,525.5 thousand MT (Nile tilapia), occupied 8.3% of major aquaculture finfish (FAO, 2020).

Mozambique tilapia ( O. mossambicus) was the first cichlid species introduced into Viet Nam from Africa in 1951 (De Silva et al 2004). With advantages of resistance to diseases, ability to survive at low oxygen tension, a wide range of salinity and temperature, and on a wide range of foods (Pandian 1988), it was quickly accepted as a production species by farmers. However, the attributes of early sexual maturation and uncontrolled breeding, the consequent overcrowding, have resulted in the loss of its interest. Nile tilapia (Oreochromis niloticus) was the second species introduced into Viet Nam from Taiwan Province of China in 1973 (De Silva et al 2004). Since then, Nile tilapia has become a substitute for Mozambique tilapia in different fish farming systems in the country. At the end of the Genetically Improved Farmed Tilapia (GIFT) Project in 1997, 20,000 fingerlings of GIFT strain of the fifth generation were transferred to Viet Nam for further selection (ADB 2005). Since 1990, several strains of red tilapia have been introduced into Viet Nam but their culture has not been popularized until 1997, after the fish was called a new Vietnamese name. The technique of all-male tilapia seed production with methyltestosterone (MT) treatment on undifferentiated fry was also transferred to Viet Nam from Asian Institute of Technology (AIT-Thailand) in 1995 (Tu, 1996 & 2006).

In Viet Nam, tilapia is commonly raised in mono- and polyculture systems in both freshwater and brackish water environments with different intensification levels. In 2015, total tilapia production was 187,000 MT from 25,748 ha of earthen ponds and 1,210,465 m³ of cages with a total value of 200 million USD. In 2017, tilapia product was exported to 68 international markets with a revenue of 45 million USD, an increase of 32% compared to 2016 (MARD, 2019). According to the development plan issued by the Ministry of Agriculture and Rural Development (MARD) in 2016, the country set targets of intensification of tilapia farming systems with total productions of 300,000 MT, of which 50-60% for export, in 2020 and 400,000 MT, of which 45-50% for export, in 2030. The export of tilapia products of Viet Nam can be only increased if the production cost is reduced and the quality is improved. Intensification of tilapia culture is the future of food production of developing countries (Balarin 1984). Major problems associated with intensive fish culture operations are the degradation of environment and the increased susceptibility of fish to infectious diseases (Welker and Lim 2011). The adverse effects associated with the use of antibiotics in aquaculture are increasing concerns of consumers. The use of probiotics, which control pathogens through a variety of mechanisms, is increasingly viewed as an alternative to antibiotic treatment (Verschuere et al 2000). A lot of studies on probiotic use in fish and shellfish aquaculture worldwide have been published, there are fewer publications on probiotic use in tilapia (Welker and Lim 2011; Hai 2015). Recently, several modern technologies, new approaches and alternative methods, including probiotics, have been applied to improve the production as well as quality of Nile tilapia (Aly et al 2008). Among all the routes of probiotic administration in aquaculture, supplementation of rearing water is the only method which is applicable for all ages of fish (Jahangiri and Esteban 2018). Among probiotic species employed in aquaculture, Bacillus spp. is likely the most widely used as a probiotic to enhance growth performance, innate immune responses, and disease resistance (Hai 2015). This study aimed to assess the ability of probiotic application as an alternative solution for the traditional method of water exchange in intensive tilapia culture with earthen ponds.

Materials and methods

Experimental design

The experiment was a completely randomized design with three treatments to assess the impacts of different methods of water quality management on growth performance and quality of tilapia cultured in earthen ponds. The treatments were included:

- Treatment 1 (CTL): no water exchange, no aeration and no probiotic application;

- Treatment 2 (WX): water exchange, no aeration and no probiotic application; and

- Treatment 2 (WXAP): no water exchange, aeration and probiotic application.

Each treatment was replicated in three 200-m² ponds with a water depth of 1.5 m. The ponds were applied CaCO₃ at a dose of 7–10 kg/100 m² and dried for 2–3 days. Water was supplied into the ponds using filter bags to eliminate unwanted animals. The ponds then fertilized with urea at a dose of 1 kg/100 m² to develop natural feed. CTL and WXAP ponds were only supplied water to compensate for evaporation and CTL ones were applied zeolite when ammonia concentration increased over 0.1 ppm. Water of WX ponds was exchanged when dissolved oxygen (DO) was lower 4 ppm and/or ammonia was higher the above toxic concentration. WXAP ponds were aerated by air-tubes distributed evenly with a distance of 2.5 m between them on pond bottom. The air-tubes were fixed on aluminum dishes to avoid bottom disturbance and water turbidity. In WXAP ponds, the air-tubes were operated when DO dropping below the required concentration and probiotic PondPlus of Bayer Company with a mixture of Bacillus spp. (B. subtilis, B. megaterium, B. amyloliquefaciens, B. licheniformis and B. pumilus, ≥ 1.0x10⁹ CFU/g) was applied when ammonia increased over the toxic value. All-male fingerlings of GIFT strain (Oreochromis niloticus) were supplied from the Tilapia selection center of Research Institute for Aquaculture No. 1 (RIA1). The fish of initial weight of 3.19±0.89 g was immersed in salt water of 2-3% for 5-10 minutes to eliminate parasites before stocking at a density of 5 ind./m².

Feeding and management

The fish was fed pelleted feeds for tilapia of GreenFeed Company twice a day at 08:00 h–09:00 h and 15:00 h-16:00 h. Crude protein concentration (25-40%) and size of the pelleted feeds, and daily feeding rate (2-5% body weight) were adjusted according to fish growth and followed recommendations of the company. At fifteen-day intervals, 30 fish individuals of each replicate were randomly sampled for size (total length and weight) measurement to adjust feeding rate. The experiment was carried out for 90 days.

Measurements

Water temperature, DO and pH were measured in the morning (06:00 h) and afternoon (15:00 h) using portable DO and pH meters of HANNA Company at a 3-day interval. Ammonia was measured weekly using indophenol blue method (APHA 1995).

The survival ratio was expressed as the percentage of surviving fish over initially stocked fish. The specific growth rate (SGR) was calculated according to Mehrara et al (2009) using the equation: SGR (%/day) = 100*(LnWf – LnWi)/T with Wi = initial fish weight (g), Wf = final fish weight (g), T = experiment period (day) and Ln = natural logarithm. The feed conversion ratio (FCR) was calculated using the equation as reported by De Silva and Anderson (1994): FCR = Fc/(Mf – Mi) with Fc = total feed consumed by fish (kg), Mi = total fish weight at beginning (kg) and Mf = total fish weight at the end of the experiment (kg). Condition factor (K) was calculated as K = 100*W/L³, where W = fish weight (g) and L = total length (cm) as reviewed by Froese (2006).

Assessment of off-flavor of the harvested fish was followed a method modified from van der Ploeg (1991) and Fitzsimmons (2008). Fillets of three randomly sampled fish of each replicate were wrapped in aluminum foil and steamed in a microwave oven for 60 seconds. Off-flavor intensity of the fillets was assessed by a judge of nine untrained persons based on a scale of five levels: 1 = very strong, 2 = strong, 3 = slight to distinct, 4 = very slight and 5 = no off-flavors. Flavor intensity was expressed by the average of level scores of the judges.

Statistical analysis

Data of the experiment were analyzed by a one-way ANOVA followed by Duncan’s multiple range test using Minnitab software version 16.0. Significant difference between treatment means was set at the probability of 0.05. Data of SR (%) were transformed to arsin√ before analyzing. Results were presented as mean ± standard deviation.

Results

Water quality

Water quality parameters are shown in Table 1. There was little change of the temperature between morning and afternoon since the experiment was carried out in rainy season and the water depth was maintained at high level (1.5 m). pH and DO in the afternoon were higher than those in the morning due to the photosynthesis of algae. Ammonia concentration of CTL (no water exchange, aeration and probiotic application) was higher than that of WX (water exchange, and no aeration and probiotic application) and WXAP (no water exchange, and aeration combined probiotic application) because the accumulation of organic matters.

Growth performance

Figure 1. Growth in total length of the fish during culture period	Figure 2. Growth in weight of the fish during culture period

The growth performance in total length and weight of the fish during the culture period was quite regular and in a same manner (Figure 1 and 2). In general, the length increase of the fish was high in the first fifteen days but slow in the last fifteen days. Different from length growth, the increase of body weight was low in first thirty days but high afterward.

Final weight of the fish of WXAP was highest, followed by WX and CTL. The trend was the same for average daily gain (ADG) and specific growth rate (SGR). There was a significant difference between means of the final weight, ADG and SGR of the fish of the treatments (p <0.05) (Table 2).

Means of total harvested biomass, total consumed feed and average feed intake (AFI) of the WXAP treatment were highest, followed by those of the WX and CTL treatments. Among the treatments, feed conversion ratio (FCR) of the WXAP was lowest (Table 3). The significant difference of the means of above parameters was found between the WXAP and CTL (p <0.05); but not between the WX and WXAP as well as between the CTL and WX (p >0.05) (Table 3).

Means of SR of the WXAP treatment were highest, followed by that of the WX and CTL. There was a significant difference of means of fish survival ratio (SR) between the treatments (p <0.05) (Table 4). High final weight (Table 2) and SR resulted in the highest extrapolated yield of the WXAP in comparison with the CTL and WX. Condition factor (K) of the fish of the WX and WXAP was better than that of the CTL (p <0.05). Lower coefficient of variation (CV) expressed even weight size of the harvested fish of the WXAP. Moreover, high scores of the WX and WXAP also pointed out the better quality in terms of off-flavor intensity of these treatments (p <0.05) compared to the rest (Table 4).

Discussion

Zhou et al (2010) found that water quality was not improved with the separate use of probiotics of Bacillus subtilis, B. coagulans and Rhodopseudomonas palustris in Nile tilapia culture. However, the study of Padmavathi et al (2012) showed that the monthly use of probiotics having Nitrosomonas and Nitrobacter resulted in reduction of ammonia and nitrite in fertilized polyculture ponds with sutchi catfish (Pangasius sutchi ), catla (Catla catla) and rohu (Labeo rohita). Sunitha and Krishna (2016) got similar results with the same probiotic species in polyculture ponds with grass carp (Ctenopharyngodon idella), catla and rohu. According to Dauda et al (2013) improved water quality was especially associated with Bacillus sp. in aquaculture. Water quality in terms of DO and ammonia concentration of the WX and WXAP ponds was improved compared to CTL ponds. Higher ammonia concentration of the CTL ponds was maybe due to the accumulation of organic wastes caused by unexchanged water. A commonly used method for water quality management in fish culture in Viet Nam is water exchange. In the case of increased shortage and degradation of running water (MNRE, 2019), the application of aeration and probiotics with mixed Bacillus species as in the WXAP ponds can be a substitutional solution for water quality management in intensive culture of tilapia. In general, the water parameters in this study were in suitable ranges for tilapia growth (Balarin and Haller 1982).

The use of probiotics as growth promoter has been applied for important species in aquaculture (see Hai 2015; Dawood and Koshio 2016). Most probiotic application in tilapia farming is as feed additives (see Welker and Lim 2011; Elsabagh et al 2018, Apiyo et al 2019). Rico et al (2013) carried out a study on the use of probiotics for internationally traded species in four Asian countries. The results showed that highest use was in Vietnamese shrimp farms (91%), followed by the tilapia (74%) and shrimp (74%) farms in Thailand, Vietnamese striped catfish farms (38%), shrimp farms in China (27%), concurrent shrimp-prawn farms in Bangladesh (9%) and Chinese tilapia farms (8%). The authors also found that 84% of interviewed farmers applying the probiotic products directly to water in order to improve the water quality and to reduce stress in the cultured species; and only 16% the farmers applying probiotics as feed additives to improve food digestibility and the health conditions of the cultured species. Zhou et al (2010) found that probiotics as water additive improved the final weight, DWG, and SGR of Nile tilapia. Among Bacillus species, the efficiency of B. coagulans was better than B. subtilis on growth performance of the fish. In the present study, the combination of aeration and mixed Bacillus spp. probiotic application in WXAP ponds resulted in the highest final weight, DWG and SGR of the cultured fish and significant difference (p <0.05) compared to the others (Table 2). The growth performance in terms of DWG and SGR of the fish of the WXAP treatment (Table 3) is higher than those (1.37 g/day and 2.55%/day, respectively) of tilapia cultured with biofloc technology (BFT) (Viet et al 2016). SGR of the fish of the WXAP treatment is also higher than that (2.31-2.34%/day) of tilapia fed with Bacillus strains mixture probiotic (Elsabagh et al 2018).

The AFI per fish of the WXAP treatment was highest, but the total harvested fish biomass of this treatment was also highest leading to its FCR was lowest and significantly different (p <0.05) from the CTL but not from the WX ones (Table 3). Elsabagh et al (2018) pointed out the ability of Bacillus supplemented in feeds in colonizing the gut of fish, enhancing the production of organic acids, activation of digestive enzymes and detoxification of the harmful constituents of feeds and maintaining a healthy gut with a subsequent improvement in nutrient digestibility and absorption. According to Avnimelech (2007), microbial flocs developed in BFT ponds are an effective food source for tilapia and the possibility to reduce feed rations in these systems. The above findings may explain for the FCR of the WXAP treatment (1.73) is higher compared to that of tilapia cultured with BFT (1.41) (Viet et al 2016) or fed with Bacillus strains mixture probiotic (1.17-1.20) (Elsabagh et al 2018). However, the FCR of the WXAP treatment is similar to that (1.6-1.8) of intensive tilapia culture without BFT and probiotic application in the country (Tien et al 2004; Viet et al 2016).

Huong et al (2014) found that more beneficial bacteria, mainly belong to Lactobacillus, Bacillus and Carnobacterium genera, accumulated in pond sediment at later stage of intensive tilapia culture. These gram-positive bacteria could improve water quality because they are better converters of organic matters back to CO₂ than gram-negative bacteria. Moreover, they could hinder the growth of harmful bacteria due to the survival competition or increase the fish health. The combination of aeration and probiotic supplement in the WXAP ponds has resulted in improving water quality and fish health leading to the highest SR compared to the others. High final weight and SR brought about the highest extrapolated yield of the WXAP in comparison with the CTL and WX. The condition factor (K) of the fish in the WXAP ponds of the present study was higher that of tilapia fed with Bacillus strains mixture probiotic (1.67-1.68) (Elsabagh et al 2018). Moreover, the combination of aeration and probiotic supplement was also improving the quality of harvested fish in terms of size even and condition factor. Off-flavor is the big problem of tilapia cultured intensively in ponds (Gutierrez et al 2013; Pimolrat et al 2015). Among methods preventing off-flavor risks of pond culture, regular water exchange or transferring off-flavored fish to clean water without the causative organisms purge the flavor-causing compounds namely methylisoborneol (MIB) and geosmin (Schrader and Rimando 2003; Fitzsimmons 2008). The results show that aeration and probiotic supplement in the WXAP ponds could remedy the off-flavor problem as the same as water exchange in the WX ones.

Conclusions

Although economic efficiency was not estimated.

• The results of this study showed that the water exchange method could increase the SR of tilapia in intensive ponds about 4.08% compared to no water exchange method and the method of aeration combined probiotic application could increase the SR of tilapia about 3.78% compared to water exchange and 8.01% to no water exchange.
• The water exchange method could increase the yield of tilapia about 12.19% compared to no water exchange and the combination of aeration and probiotic application could increase the yield of tilapia about 14.23% compared to water exchange and 28.16% to no water exchange.
• The growth performance and quality of the fish in ponds applied aeration and probiotic use were higher and better than those of water-exchange ones.
• This study clearly demonstrated that aeration combined probiotic application is the advanced method for tilapia production with high quality in intensive ponds compared to the tradition method of water exchange.
• Another benefit of this water management method is that it could contribute to sustainability of tilapia culture in term of saving water resource and remedying environmental pollution.

Acknowledgements

This work was carried out with the funding from the Department of Science and Technology of People’s Committee of An Giang province.

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