This study aimed to investigate the associations between Vibrio species and cyanobacteria in different sampling sites in a single shrimp farm, namely Pond A, Pond B, effluent water, and influent water. CCA was used to examine the correlation between these bacteria species with respect to various abiotic factors such as pH, salinity, and temperature. The results showed that there is a stronger relationship between both genera and environmental parameters than between themselves. Cyanobacteria were found to prefer salinity at all sample locations, while Vibrio species were observed to have a preference for pH levels in pond B and effluent water. Overall, these findings underscore the complexity of the relationship between Vibrio species and cyanobacteria.
Water quality parameters act as a measure of the health and well-being of shrimp culture (Carbajal-Hernández et al., 2013). Maintaining ideal environmental conditions can ensure shrimps' resilience to bacterial infections, to which they are particularly vulnerable (Cheng et al., 2003). In the sampling location where this study was conducted, pH, salinity and temperature were monitored daily by the farmers. The mean pH for all the sampling sites was recorded to be along the line of 6.14 to 7.64. A moderate increase in the acidity of the shrimp farm water was observed as the sampling progressed towards the end. This might indicate the accumulation of decaying organic matter in shrimp farm waters (Zhang, 2017). This observation can be supported by the low pH displayed by pond A, pond B and effluent that are in contact with shrimps but not from influent where the water comes into the shrimp farm from an outside source. Despite being slightly acidic, the level of pH remained in the normal range of 6.5 to 9.0 (Carbajal-Hernández et al., 2012).
In previous studies, it has been observed that shrimps are highly sensitive to even slight variations in water temperature, which can have profound effects on their size (Wyban et al., 1995). Optimal shrimp yields have been reported at water temperatures ranging from 23.5 ℃ to 25.5 ℃ or between 30 ℃ and 31.5 ℃ (Abdelrahman et al., 2019). Furthermore, the recommended range for maintaining ideal conditions during shrimp rearing is generally recognized as being between 28℃ and 32°C (Carbajal-Hernández et al., 2012). In line with these findings, consistent water temperatures averaging from 30.8℃ to 31.5℃ were recorded in this study without significant fluctuations present. The water temperatures in the shrimp farm were within the optimal range for shrimp rearing, promoting favourable growth and yield. This result can be attributed to the consistent temperature characteristics of the coastal regions in Malaysia.
As for salinity, the optimum growing performance for shrimp was discovered between 20 and 30 ppt (Gao et al., 2016). Likewise, the recorded salinity of the ponds (17.4 ppt to 24 ppt) was well kept within the ideal range in all sampling sites. Shrimps can tolerate changes in salinity level as long as proper acclimation was done before stocking the post-larvae (Rahi et al., 2021). It is clear from the environmental parameters’ data that daily monitoring in shrimp farms is essential in ensuring the best possible water quality for the shrimps' growth.
The interspecies relationship between the two genera has been proven to be an extremely complex discussion. In this research, a comparison was made between the growth of Vibrio bacteria and cyanobacteria in relation to different water parameters. Through the use of CCA, it was determined that pH, salinity, and temperature all play a role in affecting the growth of cyanobacteria; however, salinity had a more significant impact on their proliferation than other factors. This has also been proven by previous research (Silveira & Odebrecht, 2019). Salinity can affect cyanobacteria in many ways such as their cell growth and their rate of photosynthesis (Moisander et al., 2002). Cyanobacteria’s tolerance towards salt might be due to the fact that they contain a vast regulatory mechanism that allows them to acclimatize in various salt concentrations (Pade & Hagemann, 2014). Cyanobacteria’s high tolerance towards salt has been proven beneficial in the past for treating saline soil to improve rice crops (Jan et al., 2018). In pond B and effluent water, Vibrio species were found to favour pH. However, other ponds (Pond A and influent) indicate no major effect of pH towards the growth of Vibrio species. The variation in the result might indicate the optimum pH where they grow best (Keenleyside, 2019).
Our finding is consistent with previous studies where a minimal interspecies correlation between Vibrio species and cyanobacteria were documented (Julie et al., 2010; Paranjpye et al., 2015; Greenfield et al., 2017). The differences in growth patterns between Vibrio species and cyanobacteria account for this phenomenon. When compared to the overall Vibrio species which population tends to be perpetually high, the growth curve of cyanobacteria displayed a clearer consistency. They have a structure resembling the lag phase, exponential or log phase, stationary phase, and death phase like normal bacterial growth. This is possible due to the naturally slow growth rate of cyanobacteria due to their ability to carry on complex mechanisms (such as the synthetization of amino acid and utilization of carbon dioxide for photosynthesis) causing the cells to prioritize cell function over reproduction (Burnap, 2015). In contrast to cyanobacteria, heterotrophic bacteria like Vibrio species use less energy to proliferate because they consume rather than produce their food, leading to their quicker and more rapid development profile (Burnap, 2015). This observation is also in line with a previous investigation conducted in the Pacific Northwest region of the USA in 2015, which reported minimal influence on Vibrio concentration due to the low abundance of cyanobacteria gathered (Paranjpye et al., 2015). Other aforementioned studies demonstrate that the interaction between the two genera is not a result of random events, but rather influenced by various factors. The specific species involved (Julie et al., 2010), seasonal temperatures (Greenfield et al., 2017), and regional characteristics (Turner et al., 2009) play significant roles in determining this interspecies relationship. However, this finding should not completely rule out the compatibility of Vibrio proliferation with cyanobacterial blooms as 43–64% of the cyanobacterial bloom samples exhibited an association of viable but nonculturable forms of V. cholerae (Chaturvedi et al., 2015).
Throughout the sampling period, Vibrio species can be seen to either kick-start their growth slowly followed by a drastic increase in growth or maintain a constant high growth pattern above 1,000 UFC/mL which is the maximum range of acceptable Vibrio population in healthy shrimp farm water (Carbajal-Hernández et al., 2012). V. cholerae was detected at rates of 72%, 61%, 90%, and 70% in Pond A, Pond B, effluent, and influent (respectively), while V. parahaemolyticus was identified at levels of 78%, 100%, 90%, and 90% using Duplex-PCR methodology (Table 8). The detection of both Vibrio species is expected since they are naturally present in aquatic habitat (Zoqratt et al., 2018; Garibay-Valdez et al., 2020), however the high concentrations are unforeseen due to the well monitored water parameters. High concentrations of Vibrio in water are commonly viewed as a rather undesirable attribute as they can cause outbreaks of shrimp diseases (de Souza Valente & Wan, 2021). Despite that, it is important to consider that not all Vibrio species in shrimp farms are pathogenic, (Zoqratt et al., 2018; Garibay-Valdez et al., 2020), therefore, further testing for toxin genes was done to analyze the potential of the Vibrio species in causing infection. From the result, pronounced variation in the V. cholerae and V. parahaemolyticus prevalence can be explained by the halophilic profile of V. parahaemolyticus (Cartwright & Griffin, 2012) which thrives in saline water better than V. cholerae. V. parahaemolyticus can also sustain a greater range of environmental differences such as pH and temperature in coastal water than V. cholerae (Prasanthan et al., 2011). Since the sampling was done in a coastal region it is expected that V. parahaemolyticus population exceeds that of V. cholerae’s which explains the brighter bands displayed in duplex PCR.
Table 8
The summary of the PCR detection of V. cholerae and V. parahaemolyticus in Pond A, Pond B, effluent and influent.
Vibrio species | Number and percentage of positive detection |
| Pond A | Pond B | Effluent | Influent |
V. cholerae | 13/18 (72%) | 11/18 (61%) | 9/10 (90%) | 7/10 (70%) |
V. parahaemolyticus | 14/18 (78%) | 18/18 (100%) | 9/10 (90%) | 9/10 (90%) |
Cyanobacteria may be very well distinguished from other bacteria based on the characteristics of their cell dimensions, shape, color, type of branching, sheath characteristics, and cell contents (summarized in Komárek and Anagnostidis 1998, 2005; Komárek 2013; Dvorak et al., 2017). They possess easily visible features that are easy to recognize, even at lower magnifications with light microscopy (Yu et al., 2015; Albrecht et al., 2017). Staining is rarely needed in cyanobacterial microscopy due the presence of chloroplasts in their cells as natural blue-green pigments (Saini et al., 2018). Some also contains red/brownish colour due to a variety of pigments, like carotenoids and phycobiliproteins (Saini et al., 2018). In the present study, it is apparent that Pseudanabaena genus dominated the shrimp farm water as we approach the end of the sampling, significantly reducing the diversity of cyanobacteria. Aside from the reason that Pseudanabaena genus can commonly be found inhabiting planktonic water, they also are highly tolerant towards disturbance and low light when compared to other cyanobacteria genus (Nienaber & Steinitz-Kannan, 2018). Chroococcus, Phormidium, Oscillatoria and Lyngbya were among the other species that were discovered during prior samplings. In a nutshell, the study of cyanobacteria diversity in shrimp farms can lead to a better knowledge of their ecological roles, risk factors, and interactions with the shrimp farming system.
It can be concluded that environmental considerations such as pH, temperature, and salinity are more important factors in determining the growth of Vibrio species and cyanobacteria than their relationship with each other. It is suggested that reducing exposure to environmental stressors may be a more effective way to limit Vibrio and cyanobacterial growth than focusing on controlling one bacterium over another. In addition to water parameters, the monitoring of the population density of Vibrio species is suggested for the early prevention of shrimp diseases (de Souza Valente & Wan, 2021). Additionally, one limitation of our study is the focus on a specific shrimp farming location which may limit the generalizability of our findings to other geographic regions or aquaculture systems. Further research is required to determine the precise mechanisms by which these bacteria interact with their environment and to develop more targeted interventions for managing them in aquaculture systems. A conclusive study involving a multidimensional landscape with a wider scope to multiple locations can link fragmentary knowledge regarding the relationship of both genera.