Sub-lethal concentration of sulfamethoxazole affects the growth performance of milkfish (Chanos chanos), the microbial composition of antibiotic-resistant bacteria and the prevalence of sulfonamide-resistance genes in mariculture.

To investigate the impacts of sub-lethal concentrations of antibiotic agents in mariculture, culturable approach and DNA based detection were employed to isolate and analyse resistant bacteria and resistant genes in this study. Milkfish (Chanos chanos), the target rearing animal was exposed to sulfamethoxazole (SMX; 2 mg/L) for 8 weeks and resulted in reduced survival rate and weight gain to 61.9 % and 28.4 %, respectively compared to control milkfish (p < 0.001). The composition of SMX-resistant bacteria isolated from the culture water and the gastrointestinal tracts of milkfish underwent changes in response to SMX treatment with a reduced diversity. The prevalence of SMX resistant genes sul in bacterial isolates was elevated from 2.8 % of control to 100 % of SMX-administrated water. Exposure to SMX at a sub-lethal dosage enhanced the prevalence of resistance genes sul1 and sul2 in resistant bacteria, thus implying high frequency of resistance dissemination in the marine environment and surrounding ecosystems.

Effects of sulfamethoxazole and sulfamethoxazole-degrading bacteria on water quality and microbial communities in milkfish ponds.

Intensive farming practices are typically used for aquaculture. To prevent disease outbreaks, antibiotics are often used to reduce pathogenic bacteria in aquaculture animals. However, the effects of antibiotics on water quality and microbial communities in euryhaline fish culture ponds are largely unknown. The aim of this study was to investigate the interactions between sulfamethoxazole (SMX), water quality and microbial communities in milkfish (Chanos chanos) culture ponds. The results of small-scale milkfish pond experiments indicated that the addition of SMX decreased the abundance of ammonia-oxidizing bacteria (AOB), nitrite-oxidizing bacteria (NOB) and photosynthetic bacteria. Consequently, the levels of ammonia and total phosphorus in the fish pond water increased, causing algal and cyanobacterial blooms to occur. In contrast, the addition of the SMX-degrading bacterial strains A12 and L effectively degraded SMX and reduced the levels of ammonia and total phosphorus in fish pond water. Furthermore, the abundances of AOB, NOB and photosynthetic bacteria were restored, and algal and cyanobacterial blooms were inhibited. This study demonstrate the influences of SMX on water quality and microbial community composition in milkfish culture ponds. Moreover, the use of the bacterial strains A12 and L as dual function (bioaugmentation and water quality maintenance) beneficial bacteria was shown to provide an effective approach for the bioremediation of SMX-contaminated euryhaline milkfish culture ponds.

The effects of marine farm-scale sequentially integrated multi-trophic aquaculture systems on microbial community composition, prevalence of sulfonamide-resistant bacteria and sulfonamide resistance gene sul1.

Aquaculture, one of the most important food production practices worldwide, faces serious challenges of mitigating the detrimental impacts of intensive farming on the environment and increased prevalence of antibiotic resistance. To develop an environment-friendly aquaculture system, a land-based and farm-scale sequentially integrated multi-trophic aquaculture (IMTA) system was established for farming Chanos chanos in southwestern Taiwan. In this system, fishes are cultured in combination with organic extractive shellfish and inorganic extractive seaweed. This study aimed to evaluate the prevalence of sulfonamide-resistant bacteria, microbial community structure, and occurrence of sulfonamide resistance genes in the IMTA and traditional aquaculture systems. Water and sediment samples were collected before raising and after harvesting C. chanos. Our results showed that the occurrence of sulfonamide-resistant phenotypes in the IMTA system was comparable with that in influent seawater, while the traditional system exhibited a high sulfonamide resistance rate. Additionally, the traditional system resulted in a deviation of the bacterial community structure from that of seawater. In the water samples from the IMTA system and influent seawater, Proteobacteria and Bacteroidetes were the two dominant phyla, representing approximately 75% and 15% of the community, respectively. In the traditional system, Actinobacteria, constituting 39% of the community, was the dominant bacterial phylum. Thirty-one sulfonamide-resistant bacterial species were isolated. In conclusion, a sequentially IMTA system showed superior ability to maintain the prevalence of antibiotic resistance and the integrity of the bacterial community structure compared to the traditional farming system, representing a potentially valuable aquaculture system for preserving the sustainability of the marine environment.

Androgens stimulate sex change in protogynous grouper, Epinephelus coioides: spawning performance in sex-changed males.

We examined the efficacy of androgens (1.0 mg/kg body mass), testosterone (T), 11-ketotestosterone (11-KT), 17alpha-methyltestosterone (MT), testosterone propionate (TP) or androgen mixture (T, MT and TP in an equal ratio), for induction of sex change in protogynous orange-spotted grouper, Epinephelus coioides. The spawning performance in sex-changed males was also investigated. MT and androgen mixture at a dose of 1.0 mg/kg BW induced a sex transition and completion of spermatogenesis up to the functional male phase. The androgen mixture was most effective. Significantly, higher plasma T levels were found in MT and androgen mixture groups compared to control and other androgen implantation (T, TP or 11-KT) groups. We found that plasma levels of estradiol-17beta (E2) or 11-KT were not different among treated groups. Sex-changed males could successfully fertilize mature eggs. Fertilization and hatching rates were of 23.5-70.4% and 8.4-44.6%, respectively. The data demonstrated that induction of sex change by exogenous androgens in groups could apply to the aquaculture field for seed production.