Single-cell proteins are attracting growing attention as viable alternatives for fishmeal (FM) in aquatic feed. Methanotroph (Methylococcus capsulatus, Bath) bacteria meal FeedKind^® (FK) is a type of single cell protein with high protein content (75.14%) and desirable amino acids profile, produced by Methylococcus capsulatus (Bath) living on methane consumption. The present study evaluated the potential of replacing FM with FK in the diet of black sea bream (Acanthopagrus schlegelii). Five iso-energetic and iso-nitrogenous diets were designed with FK replacing 0, 4.13, 8.27, 16.53, and 24.80% FM protein in the basal diet (40% FM content), respectively. All the diets were fed to three replicates of fish (initial weight 6.56 ± 0.02 g) for 70 days. After the feeding trial, replacing dietary 8.27% FM protein with FK significantly improved the weight gain and specific growth rate of fish (P < 0.05), while other groups showed no significant difference in the growth performance (P > 0.05). The fish fed diets with 8.27 and 16.53% replacement levels exhibited significantly increased feeding rates. The 8.27% FK diet significantly increased the whole-body and muscle crude protein contents, apparent digestibility of crude lipid, foregut, and midgut amylase activities. The microvillus density in the midgut of fish fed the 24.80% FK diet significantly increased. The diet with 8.27% FK increased the serum triglyceride content of the fish, while the 24.80% FK diet reduced the serum triglyceride, total cholesterol, and low-density lipoprotein cholesterol contents of the fish. In conclusion, the results indicated that replacing dietary FM protein with up to 24.80% FK had no adverse effects on the growth of black sea bream, whilst replacing 8.27% FM protein with FK enhanced its growth performance and feed utilization.

China is the largest food fish producer in the world. Chinese consumers normally purchase fish that are still alive to ensure freshness. Therefore, the live transport of fish is important in China’s aquaculture, although it carries potential risks for animal welfare. This study investigated the attitudes and knowledge of stakeholders within Chinese aquaculture towards the live transport and welfare of fish. Semi-structured interviews were conducted with 12 participants who were involved with the aquaculture industry in China. Most participants self-rated their transport-related knowledge as moderate and had some understanding of animal welfare, although this term was generally considered only relevant to terrestrial animals. Participants’ responses indicated that the live transport of fish occurs frequently in China, generally using sealed tanks, plastic bags, and foam boxes, in purpose-built vehicles. Seasonal changes, such as changes in ambient and water temperature, are considered to be important contributors to successful live transport, as well as sufficient oxygen supplies and stocking density. The use of anesthetics was not commonly reported, particularly in food fish, and fish capture is predominantly by conventional dipnets. The health status of transported fish is determined mostly by morphology (body injury, body or eye color, and fin condition), as well as vigor and swimming ability. Our results indicate that live transport poses a number of welfare risks to fish but that participants in the process associated welfare concerns more with terrestrial animals, not fish.

The live transport of farmed fish is an important practice in Chinese aquaculture due to consumer preferences in its domestic market. However, live transport can be stressful for fish and may cause many welfare issues. This study aimed to examine the effects of transport density on the welfare of largemouth bass (Micropterus salmoides). Adult fish were allocated to four experimental treatments in a two‐factor design (N = 5 groups per treatment). Factor one was stocking density of either 39 (low density) or 78 (high density) g L⁻¹. Factor two was transport, with half of the fish groups exposed to simulated transport stress for 3 h using a motion platform, and the other half kept in static tanks for the same length of time. Baseline behavior and physiology were determined from a subset of fish after acclimation but before selection into groups and application of transport. To determine the effects of transport, stocking density, and their interaction on the experimental groups, physiological sampling and behavioral recording were carried out immediately after simulated transport, and water quality was measured both before and after transport. Changes in water quality were observed between two timepoints, with decreased dissolved oxygen levels and increased water temperature. Total ammonia nitrogen levels significantly increased in all treatments over time, particularly in the high‐density groups. Fish ventilation rates were significantly elevated in the groups kept at a high stocking density regardless of whether they also experienced transport stress. Fish transported at a high stocking density also showed more fear‐related behaviors such as freezing and thigmotaxis than non‐transported groups. Serum cortisol, catalase, and aspartate transaminase levels were significantly higher in the transported treatment groups compared to the baseline fish, but no difference was found for serum glucose, lactate, and glutathione peroxidase. We concluded that 3 h of simulated transport was stressful to largemouth bass kept at 78 g L⁻¹, as evidenced by altered fish physiological and behavioral indicators of stress, as well as deteriorated water quality. Additionally, we identified a positive correlation between serum and skin mucus samples for cortisol, glucose, and lactate in transported fish, providing important information for developing less invasive methods for the welfare assessment of largemouth bass.

The interactive effect of dietary inactivated Lactobacillus plantarum and berberine on black sea bream, Acanthopagrus schlegelii, was investigated with three diets designated as D1 (Con: basal diet), D2 (LP: basal diet + 400 mg/kg L. plantarum), and D3 (LPBB: basal diet + 400 mg/kg L. plantarum + 50 mg/kg berberine) and fed to juvenile black sea bream ( g) for 56 days. The growth performance and feed utilization parameters, as well as intestinal trypsin activity, were significantly improved in the LP and LPBB groups ( ). Fish fed the LPBB diet showed better serum and hepatic antioxidant capacity, whilst the LP group had better hepatic antioxidant capacity, than the control fish ( ). Intestinal IgM and C3 levels significantly increased in the LPBB fish than the rest of the groups ( ). NF-κB was significantly upregulated in the LP group ( ). Nrf2 and IL-10 were significantly upregulated, whilst Keap1b and NF-κB were significantly downregulated in the LPBB group ( ). These findings show that a combination of inactivated L. plantarum and berberine in the diet of black sea bream can improve the immune response and antioxidant capacity than a diet with only the inactivated probiotic, whilst both diets can equally improve growth performance.

In China, the world’s largest fish producer, fish are generally transported live from farms to points of sale or processing. However, there is little published literature on live fish transport in China or aquaculture stakeholder attitudes towards fish welfare. This study investigated transport practices within the Chinese freshwater fish industry and opinions around fish welfare among aquaculture stakeholders. Online and face-to-face surveys were conducted with 252 participants from 18 provinces across China, with more than half from Hunan Province. Participants represented the fish production, sales, government, and research sectors. Responses indicated that over 75% of freshwater fish are transported live, generally in compartmented tanks with water-holding systems on purpose-built trucks. Destinations were primarily wholesale markets with journey durations ranging from less than one hour, up to eight hours. Dissolved oxygen, water temperature, and staff experience were reported as the most important factors affecting fish welfare during transport. While over 60% of participants were unaware of the specific term “animal welfare”, three-quarters recognised a link between fish welfare and product quality. A similar proportion acknowledged that fish are sentient, with respondents educated at the tertiary level having greater awareness of, and concern for, fish welfare. As the concept of animal welfare is emerging among aquaculture stakeholders, these findings provide valuable insights into transport practices and opportunities for improving both animal welfare and product quality. The results also contribute to a better understanding of the potential welfare risks to fish during transport in China, especially among Chinese fish welfare researchers.