Niti Chuchird

Vibrio spp. are the most common opportunistic pathogens in shrimp farms, and drug‐resistant Vibrio spp. pose a major threat to both shrimp and human health. The current study investigated species diversity and antimicrobial susceptibility of Vibrio spp. from Pacific white shrimp ( Litopenaeus vannamei ) in Southern Thailand. Shrimp were collected from ten intensive farms with a history of disease outbreaks. Vibrio spp. were isolated from the hepatopancreas, identified to species level via 16S rRNA sequencing, and tested for minimum inhibitory concentrations (MICs) against eight antibiotics. A total of 27 Vibrio species were recovered. V. parahaemolyticus was the most frequently recovered species among the selected isolates, followed by V. alginolyticus and V. harveyi . Overall, the isolates were susceptible to oxytetracycline, doxycycline, ciprofloxacin, enrofloxacin, and florfenicol, with MIC ₅₀ ranging from ≤ 0.25 to 2 μg/mL. Conversely, most Vibrio spp. were resistant to amoxicillin, ceftriaxone, and sulfadimethoxine, with MIC ₅₀ values of at least 128 μg/mL. To our knowledge, this study provides the first evidence of high‐level ceftriaxone resistance in Vibrio spp. from farmed shrimp. To distinguish fully susceptible bacteria (wild type) from those that develop acquired resistance, epidemiological cut‐off (CO _WT ) was determined. The CO _WT for florfenicol was calculated as ≤ 4 μg/mL; when this threshold was applied to the Vibrio spp. isolates, 83.10% were classified as wild type. Our findings highlight the need for strict regulation of antibiotic use in shrimp aquaculture to minimize the emergence and spread of antibiotic‐resistant bacteria.

Yeast nucleic acids and free nucleotides (yeast RNA + NT) is a functional feed additive with health‐promoting effect. This study aimed to evaluate the effect of dietary yeast RNA + NT (from Kluyveromyces fragilis ) on the health conditions, hypoxic stress tolerance and disease resistance in juvenile Pacific white shrimp ( Litopenaeus vannamei ). Shrimp were fed diets supplemented with 0, 0.25, 0.50 and 0.75 g·kg ⁻¹ yeast RNA + NT for 45 days, followed by challenges with hypoxic stress and Vibrio parahaemolyticus (AHPND). Results showed that yeast RNA + NT supplementation at 0.50 g·kg feed ⁻¹ could significantly improve body weight (3.93 g), FCR (1.20), trypsin activity (78.02 mU·mg protein ⁻¹ ) and trypsin‐to‐chymotrypsin ratio (5.03) compared to the control (3.34 g, 1.59, 64.70 mU·mg protein ⁻¹ and 3.78, respectively). All three yeast RNA + NT groups had significantly higher survival rates and lower Vibrio spp. counts in the hepatopancreas. The highest immune responses were observed in the yeast RNA + NT at 0.75 g·kg feed ⁻¹ group. Survival rates under hypoxia were significantly higher in the yeast RNA + NT at 0.50 (81.67%) and 0.75 g·kg feed ⁻¹ (80.00%) compared to the control (45.00%). Notably, the 0.75 g·kg ⁻¹ group exhibited the highest resistance to AHPND, with a survival rate of 65.00% compared to 43.33% in the control. These findings suggest that 0.50 g·kg ⁻¹ is optimal for growth promotion, whereas 0.75 g·kg ⁻¹ maximises immune function and resistance to hypoxia and bacterial infection.

Antimicrobial drugs are commonly used for the treatment of bacterial diseases in cobia ( Rachycentron canadum ), but information regarding the rationale of their therapeutic use, such as pharmacokinetics (PK), optimal dosages, and withdrawal time (WDT) in this species is very rare. The present study evaluated the PK characteristics of florfenicol (FF) in cobia at 25°C after a single oral administration of 10 mg/kg via medicated feed. FF in the serum was determined by an HPLC method and the PK parameters were analyzed by a one‐compartmental model. In tissue depletion and drug WDT study, cobia were fed with FF medicated feed at 10 mg/kg once daily for 5 days. The WDT was determined by linear regression analysis using the sum of FF and its metabolite florfenicol amine as the marker residue. The results revealed that FF has desirable PK characteristics in cobia, including a high peak serum concentration ( C _max , 9.08 μg/mL), a large area under the serum concentration‐time curve (AUC, 182.68 h·μg/mL), and a moderately long elimination half‐life ( t _1/2K , 10.22 h). The optimal dosage for a minimum inhibitory concentration (MIC) of 2 μg/mL at 25°C was 6.23 mg/kg/day. The WDT was calculated to be 5 days based on muscle/skin and 6 days based on serum depletion. Since serum sampling can reduce animal use, it warrants further investigation despite not being an official target tissue for WDT. Our findings indicated that FF is a good choice for treating bacterial diseases in cobia due to its favorable PK profile and short WDT.

Drug leaching from medicated feeds into water reduces the available drug for absorption in the gut and causes negative effects in environments. The objectives of this study were to evaluate various top‐coating materials in reducing the leaching of florfenicol (FF) from shrimp medicated feed and to determine the drug concentrations in the body of Pacific white shrimp ( Litopenaeus vannamei ) fed medicated feed top‐coated with tuna oil, chitosan, pectin, hydroxypropyl methylcellulose (HPMC), carboxymethyl cellulose sodium (CMC), and ethylcellulose (EC). FF concentrations that leached from the medicated feeds into water were analyzed using the HPLC method. Drug concentrations in the hemolymph and muscle of shrimp following oral administration were also analyzed. The results revealed that chitosan was the most effective material in reducing drug leaching, with only 27.8% leaching rate at 120 min. Tuna oil had the highest leaching rate (71.6%). Shrimp fed chitosan‐coated medicated feed had significantly higher FF levels in hemolymph (2.04 μg/mL) and muscle (0.92 μg/g) than the other coating material groups. The tuna oil group had the lowest drug levels (0.20 μg/mL and 0.34 μg/g, respectively). These findings indicate that chitosan is the most effective in minimizing drug leaching and also exhibits the highest drug absorption in shrimp.

Pale shrimp disease is an emerging threat in Thailand, characterized by pale body coloration in Pacific white shrimp ( Litopenaeus vannamei ). Although the etiology had been identified as Photobacterium damselae subsp. damselae , the disease effects on gut microbiome remain poorly understood. This study investigated changes in the gut microbiota of Pacific white shrimp suffering from pale shrimp disease (diseased group) compared to disease-free shrimp (healthy group) collected from Surat Thani Province, Thailand. DNA extracted from the intestinal samples was subjected to 16S rRNA metagenomic sequencing, followed by taxonomic identification, diversity analyses, and functional prediction of the metabolic pathways. Despite a limited number of biological replicates, the occurrence of pale shrimp disease was able to reveal alterations in intestinal microbial composition, diversities, and functional features compared to the healthy shrimp. In most cases, the intestinal microbiota of the diseased shrimp were dominated by only 2 genera of bacteria, i.e., Photobacterium (54.63–70.53%) and Vibrio (24.94–26.12%), which together accounted for 79.58–95.47% of the total bacterial community. α-diversity, as indicated by the observed features, Shannon, and Simpson indices, was significantly decreased, and dominance was significantly increased in the diseased shrimp compared to healthy shrimp. Likewise, β-diversity was significantly different between groups; PCoA of un-weighted and weighted UniFrac clearly distinguished intestinal microbiota of the shrimp into 2 clusters, and ANOSIM of these data revealed statistical differences between groups, suggesting different microbiota communities between healthy and diseased shrimp. Moreover, diseased shrimp had significantly higher predicted functional features associated with bacterial virulence factors and antibacterial resistance. These exploratory findings suggest an association among pale shrimp disease, gut microbiota dysbiosis, and the proliferation of opportunistic taxa, particularly Photobacterium .

Ecytonucleospora hepatopenaei (EHP) infection in Penaeus vannamei causes significant economic losses in shrimp aquaculture due to growth retardation. Unable to generate ATP, EHP obligately relies on host energy production to survive. We hypothesize that EHP may potentially disrupt its host’s lipid metabolism as lipid is the most energy-dense resource. To this end, the effects of EHP infection on lipid metabolism were investigated by evaluating activities and expressions of digestive enzymes, accumulation of lipid droplets, and expression of genes involved in lipid breakdown and synthesis. Results revealed that EHP infection progressively diminished digestive enzyme activities, leading to reduced nutrient availability. A persistent reduction of lipid droplet accumulation was detected from the onset of EHP infection. The marked decrease in the early stages was attributable to increased lipid droplet breakdown outpacing lipid synthesis. In the later stage, a partial recovery of lipid synthesis gene expression was observed; however, this was insufficient to counteract increased lipid breakdown, as genes in this pathway were upregulated. Ultimately, this imbalance resulted in a marked depletion of lipid droplets. These findings highlight how EHP infection chronically impairs digestion, drains lipid reservoir of its host and, eventually, retards growth. In terms of a potential practical solution, this study implies that dietary lipid supplementation might alleviate the metabolic disruption of EHP and, thereby, lessen the extent of growth retardation in infected population.

Polyphenol‐rich sugarcane extract (PRSE) is a product of sugarcane obtained from the sugar refinery industry and can potentially be used as a feed additive in farmed animals. The purposes of the current study were to evaluate the effects of PRSE on growth performance, survival, immune responses, and resistance to Vibrio parahaemolyticus and white spot syndrome virus (WSSV) infections of Pacific white shrimp, (Litopenaeus vannamei). In Experiment 1, the postlarvae were randomly divided into five groups (8 replicates/group and 80 shrimp/tank) and fed commercial feeds supplemented with PRSE at the rate of 0 (control), 0.2, 0.4, 0.6, and 0.8% of the diets four times/day for 60 days to evaluate the body weight, survival rate, and immune function. In Experiment 2, the juvenile shrimp from Experiment 1 were randomly redistributed into six groups (four treatment groups as in Experiment 1, positive control, and negative control with 3 replicates/group and 30 shrimp/tank) and challenged with either V. parahaemolyticus or WSSV via immersion (10⁵ colony‐forming units/mL) and oral (feeding with infected tissues) routes, respectively, to evaluate disease resistance. Our results demonstrated that shrimp body weight for the 0.8% PRSE group was significantly greater than the other groups, and those fed 0.4%–0.8% PRSE demonstrated a significant improvement in survival, total hemocyte count, phagocytic activity, phenoloxidase activity, and superoxide dismutase activity compared with the controls. On day 7 following the V. parahaemolyticus challenges, the survival rates of the 0.4%–0.8% PRSE‐fed shrimp (70%–73%) were significantly greater than the control counterpart (46%). However, shrimp challenged with WSSV suffered severe mortality regardless of the treatment groups, but those treated with 0.4%–0.8% PRSE showed delayed mortality. In conclusion, results suggested that dietary PRSE supplemented at 0.4%–0.8% diets were beneficial for improving overall health and disease resistance in shrimp culture.

Free fatty acids have long been used as dietary supplements in aquaculture, but the application of monoglycerides has increased interest in more recent times. The study aimed to investigate the effects of dietary short- and medium-chain fatty acid monoglyceride and cinnamaldehyde (SMMG) on the growth performance, survival, immune responses, and tolerance to hypoxic stress of Pacific white shrimp (Litopenaeus vannamei). In Experiment 1, shrimp post-larvae were divided into 4 groups with 6 replicates and fed with diets supplemented with 0 (control), 0.3, 0.4, and 0.5% diet for 30 days. The final body weight and survival rate were determined. In Experiment 2, the juvenile shrimp from Experiment 1 were subjected to hypoxic stress conditions (dissolved oxygen level 2–2.5 mg/L) for 14 days, then the specific growth rate (SGR), survival rate, intestinal Vibrio spp. count, immune responses, and histopathological change of the hepatopancreas were analyzed. Following the 30-day feeding trial, the results revealed that the final body weight and survival of the 0.3–0.5% SMMG groups (2.81–3.06 g and 74.00–84.33%, respectively) were significantly higher than the control shrimp (1.96 g and 68.33%, respectively). In the hypoxic stress experiment, the survival rates of shrimp fed 0.4–0.5% SMMG (71.67–80.00%) were significantly higher than the control (51.67%). Although the SGR were not affected by SMMG supplementation, all immune parameters evaluated were significantly enhanced, and the intestinal Vibrio spp. counts were significantly decreased in the 0.4–0.5% SMMG-fed shrimp; the histopathological structure of the hepatopancreas was also improved in these shrimp compared to the control. Our findings indicated that SMMG as a feed additive has beneficial effects in improving shrimp health and increasing tolerance to hypoxic conditions.