A 90-day feeding trial was conducted to evaluate the effects of formic acid (FA) and astaxanthin (AX) on growth, survival, immune parameters, and tolerance to Vibrio infection in Pacific white shrimp. The study was divided into two experiments. In experiment 1, postlarvae-12 were randomly distributed into six groups and then fed four times daily with six experimental diets contained 0.3 % FA, 0.6 % FA, 50 ppm AX, 0.3 % FA + 50 ppm AX, 0.6 % FA + 50 ppm AX, or none of these supplements (control diet). After 60 days of the feeding trials, the body weight of all treatment groups was not significantly different from the control group, although shrimp fed formic acid had significantly lower body weight than shrimp fed 50 ppm AX. However, the 0.6 % FA + 50 ppm AX group had a significantly higher survival rate (82.33 ± 8.32 %) than the control group (64.33 ± 10.12 %). In experiment 2, Vibrio parahaemolyticus was added to each tank to obtain a final concentration of 104 colony-forming units/mL. Each treatment group received the aforementioned diets for another 30 days. At the end of this experiment, there was no difference in the weight gain among all experimental groups. However, the survival rate of shrimps whose diet included FA, AX, and their combination (in the range of 45.83–67.50 %) was significantly higher than the control group (20.00 ± 17.32 %). FA-fed shrimps also had significantly lower total intestinal bacteria and Vibrio spp. counts, while immune parameters [total hemocyte count (THC), phagocytosis activity, phenoloxidase (PO) activity, and superoxide dismutase (SOD) activity] of AX-fed groups were significantly improved compared with the other groups. In conclusion, FA, AX, and their combination are useful in shrimp aquaculture.Electronic supplementary materialThe online version of this article (doi:10.1186/s40064-015-1234-x) contains supplementary material, which is available to authorized users.

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Anesthetic agents are often used in fish experiments to reduce the stress and struggle and to improve animal welfare. The present study aimed to determine the optimal doses and serum minimum effective concentration (MEC) of tricaine methanesulfonate (MS-222), 2-phenoxyethanol (2-PE), and eugenol (EUG) in Nile tilapia. Twenty-one fish were immersed in three different doses of each anesthetic and the minimal dose that produce stage III anesthesia within 5 min, maintain anesthesia status for 3 min, and recover within 5 min was considered the optimal dose. The serum concentrations of anesthetics immediately after the fish reached stage III anesthesia was defined as the MEC. The results revealed that the anesthetics dose-dependently shorten the induction time while the effect of doses on the recovery times were variable. The determined optimal doses for MS-222, 2-PE, and EUG were 300, 900, and 90 ppm, respectively. The MECs were 70, 263, and 53 µg/mL, respectively, about two to four times lower than the optimal doses and were independent of the doses. After immersion stopped, the serum concentrations decreased by >90% within the first hour and >99% after 4 h. Our research provides useful information for a smooth fish handling and design for researches requiring stage III anesthesia.

Optimized dosing regimen is key to the effective use of antibacterials and to minimizing drug‐related side effects. The current study established a pharmacokinetic–pharmacodynamic (PK‐PD) model for the determination of optimal antibacterial dosing regimen in fish taken into consideration the temperature‐dependent PK and the pathogen‐dependent antimicrobial susceptibility, using florfenicol (FF) in Nile tilapia as an example. The calculated optimal dosages significantly varied by temperature and target MIC levels, ranging from 2.23 (MIC 1 µg/ml at 24°C) to 34.88 mg kg−1 day−1 (MIC 4 µg/ml at 32°C). The appropriateness of the calculated dosages was successfully verified by the in vivo studies. After 5 days of oral administration of the calculated optimal dosage at 24°C, the predicted plasma drug values were in line with the mean observed Cmin(ss) while at 28 and 32°C underestimation of the Cmin(ss) in a dose‐dependent manner was observed and likely due to the occurrence of non‐linear PK at high dosages. The averaged serum protein binding of FF was 19.1%. Our results demonstrated the appropriateness and clinical applicability of the developed PK‐PD approach for the determination of optimal dosing regimens at given temperatures and MICs. Saturation metabolism and PK non‐linearity of FF in tilapia warrant further study.

Isoquinoline alkaloids (IQs) from Macleaya cordata are promising natural products for enhancing the growth performance and overall health condition of farmed animals. The present study aimed to investigate the effects of two formulas of IQ extract, provided in either a powdered formula (IQ-E) or a water-soluble, granulated formula (IQ-WS) and containing the main active component sanguinarine at a concentration of 0.5% and 1%, respectively, on the growth, survival, immune response, and resistance to Vibrio parahaemolyticus infection of Pacific white shrimp (Litopenaeus vannamei). In Experiment 1, the postlarvae were divided into five groups (four replicates/group and 100 shrimp/tank) and fed four times/day for 30 days with a control feed, IQ-E at 200 or 300 mg/kg of feed, or IQ-WS at 100 or 150 mg/kg of feed. In Experiment 2, the surviving shrimp from Experiment 1 were redistributed into six groups (four treatment groups as in Experiment 1 plus the positive and negative controls with four replicates/group and 30 shrimp/tank) and challenged with V. parahaemolyticus by immersion at a concentration of 103 colony-forming units (CFU)/mL and were fed with the same diets for another 14 days. The results revealed that all IQ-fed shrimp in Experiment 1 had significantly enhanced survival rates and immune parameters (total hemocyte count and phagocytic, phenoloxidase, and superoxide dismutase activities) compared to the control group, even though the growth performances were similar across all groups. In Experiment 2, all IQ-fed groups showed better growth performance and survival rates compared to the positive control. Other than in the positive control group, no histopathological lesions in the hepatopancreas and the intestine were found. In summary, the current study demonstrated the benefits of using IQs from M. cordata as feed additives for improving the growth performance, survival rate, immune responses, and resistance to vibriosis of Pacific white shrimp.

The study was designed to characterize the plasma pharmacokinetics and tissue depletion profiles (including eggs) of cyromazine (CYR) in chickens following oral administration alone or in combination with melamine (MEL). In order to assess the pharmacokinetic profile of CYR, chickens were administered 1 or 10 mg/kg (single oral doses), whereas residue studies were conducted in chickens fed CYR alone (5 or 10 mg/kg) or CYR (5 mg/kg) and MEL (5 mg/kg) for a period of 14 days. Estimates for the apparent volume of distribution (1.66 L/kg), clearance (7.17 mL/kg/min), and elimination half-life (2.82 h) were derived by noncompartmental analyses. The highest concentration of CYR occurred in liver but fell below detectable limits within 3 days following drug withdrawal from feed. Combined feeding of MEL with CYR did not significantly alter CYR tissue levels. CYR residues were detected only in egg white and were undetectable at the 2nd day postadministration. No MEL was found in eggs unless it had been added to the feed, and when present, it almost exclusively restricted to the egg white. Based upon the results of this initial study of CYR pharmacokinetics and residue depletion, it appears that use of CYR as a feed additive either alone (5 or 10 mg/kg) or in combination with MEL (both agents at 5 mg/kg) does not produce unsafe residue levels in edible products as long as appropriate withdrawal periods are followed for tissues (3 days) and eggs (2 days). However, our results indicate that adoption of a zero-day withdrawal period should be reconsidered in light of these results.

Prudent antimicrobial use requires knowledge of pharmacokinetics (PK) in a specific fish species which in turn depends on water temperature and salinity. Although the influence of each individual factor is known, the combined effect is less clear. The objective of the current study was to investigate the effect of temperature and salinity concurrently on the PK of florfenicol (FF) in Nile tilapia reared in brackish water. Twenty-eight fish were divided into four groups and kept at one of two temperatures (24 vs. 32°C) and two salinity levels (5 vs. 15 ppt). The FF was administered at a single dose of 15 mg/kg body weight via oral gavage. The serum concentrations were analyzed by HPLC method and the PK parameters were analyzed by a 2-compartmental model. The result revealed that at 32°C, the elimination half-lives (t1/2β), time to reach the peak concentration (Tmax), area under the serum concentration-time curve (AUC), and mean residence time (MRT) were significantly decreased, while the clearance relative to bioavailability (CL/F) significantly increased compared to those at 24°C. The extents of these PK changes were similar at the two salinity levels. On the contrary, increasing the salinity from 5 to 15 ppt at a given temperature level produced no significant change in the PK behavior. Our finding indicated that only water temperature, but not salinity, is the major determinant factor governing the FF fate in the fish body.