This study investigated the potential of dietary gamma-aminobutyric acid (GABA) inclusion to mitigate acute temperature stress impacting the physiological resilience of juvenile olive flounder (Paralichthys olivaceus). A total of 360 juvenile fish, with an average initial weight of 12.97 ± 0.1 g (mean ± SEM), were randomly assigned in triplicate to 18 tanks (20 fish per tank) and reared at 19.5 °C for 8 weeks, with bi-monthly collection of growth performance data. The fish were fed one of six experimental diets: control (GABA74), 174 ppm of GABA (GABA174), 275 ppm of GABA (GABA275), 396 ppm of GABA (GABA396), 476 ppm of GABA (GABA476), and 516 ppm of GABA (GABA516). At the end of the trial, one group of fish was subjected to lethal temperature stress (31 °C) for 48 h, while another was exposed to acute temperature stress (29 °C) for 6 h. Growth performance remained relatively stable across all inclusion levels (p > 0.05), with the final body weight (FBW) ranging from 48.2 ± 0.3 g (GABA174) to 50.3 ± 0.6 g (GABA516) and the feed conversion ratio (FCR) varying between 2.06 ± 0.07 (GABA396) and 2.35 ± 0.07 (control). There were no significant differences in average whole-body composition across all dietary treatments, with moisture content ranging from 74.8 to 75.0%, crude protein from 17.8 to 18.2%, crude lipid from 2.89 to 3.15%, and crude ash from 3.62 to 3.80%. Similarly, there were no significant differences in cumulative survival rates during lethal temperature exposure between the GABA-supplemented groups and the control group, with an average of 28.5 ± 4.6%. Additionally, GABA inclusion did not significantly alter plasma-free amino acid profiles, antioxidant enzyme activities, or immune functions (p > 0.05). However, temperature significantly reduced the levels of superoxide dismutase (SOD) from 3.34 ± 0.17 to 2.29 ± 0.36 µg/mL and increased the levels of glutamate oxaloacetate transaminase (GOT) from 17.1 ± 0.8 to 46.3 ± 6.2 U/L, glutamate pyruvate transaminase (GPT) from 14.4 ± 0.6 to 30.2 ± 2.1 U/L, glucose (GLU) from 13.3 ± 0.5 to 68.7 ± 7.7 mg/dL, total protein (TP) from 2.94 ± 0.00 to 3.21 ± 0.1 g/dL, and cortisol from 5001 ± 147 to 6395 ± 194 ng/mL. Furthermore, no significant changes were observed in the expression of key stress-related genes, including heat shock proteins (hsp60, hsp70, and hsp90) and the warm water acclimation-related gene wap65. This study establishes the safety of GABA as a dietary inclusion for olive flounder and highlights its potential to enhance stress resilience in aquaculture. However, the effectiveness of GABA-based interventions could depend on critical factors such as dosage, stress duration, and species-specific responses. Our findings highlight the need for further research to optimize GABA inclusion strategies, particularly with consideration for long-term physiological impacts.

A six-week feeding trial was conducted to assess the safety of single-domain antibodies (sdAbs) derived from camelids against the white spot syndrome virus (WSSV) (WSSVvp28 was used as the antigen), focusing on the whole-organism responses and molecular-level changes in juvenile whiteleg shrimp (Litopenaeus vannamei). Five experimental diets with varying levels of sdAbs were formulated: CON (no sdAb supplementation); SDA_8.2 (8.20% of sdAbs); SDA_16.4 (16.40% of sdAbs); SDA_24.6 (24.60% of sdAbs); and SDA_32.8 (32.80% of sdAbs). In the CON diet, 450 mL of water per kg of diet (45%) was used to form a feed dough, while sdAbs were used to replace the water in the treatment diets. A total of 450 shrimp, with an initial body weight of 3.27 ± 0.02 g (mean ± SEM), were randomly distributed in 15 tanks (30 shrimp per tank; three tanks per treatment). Each tank was filled with 30 L of seawater (77 L capacity) in an indoor semi-recirculating system with a constant water flow rate of 1.2 L min⁻¹. The photoperiod was maintained at 12 h of light and 12 h of dark. The water temperature, pH, salinity, and dissolved oxygen were 27.3 ± 0.1 °C, 7.61 ± 0.01, 34 ± 1 ppt, and 5.94 ± 0.04 mg L⁻¹, respectively. During the feeding trial, the shrimp were fed the experimental diet (40% protein and 11% lipid) three times a day for six weeks. Following the feeding trial, an acute cold-water-temperature stress test was conducted by abruptly exposing the shrimp from each treatment to 15 °C for 4 h, down from 27 °C. The results showed no significant differences in the growth performance (weight gain, feed utilization efficiency, survival, etc.), plasma metabolites (aspartate aminotransferase activity, alanine aminotransferase activity, total protein, and glucose), or antioxidant enzymes (superoxide dismutase and glutathione peroxidase) among all the experimental diets (p > 0.05). In the acute cold-temperature stress test, there was no significant interaction between sdAb supplementation and temperature stress, nor any main effect from either factor, except for the main effect of temperature stress on the glucose levels, which was significantly higher in shrimp exposed to cold-temperature stress (p < 0.05). The next-generation sequencing of differentially expressed genes (DEGs) in the hepatopancreases of shrimp fed the CON, SDA_16.4, and SDA_32.8 diets, followed by Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses, indicated that DEGs were significantly enriched in signaling pathways associated with growth, cold stress, and antioxidant systems. Overall, the results from conventional measurements suggest that the use of sdAbs against the WSSV may be safe for juvenile whiteleg shrimp. However, findings from the sophisticated analysis indicate that further research is needed to understand the molecular mechanisms underlying the observed changes, and to evaluate the long-term effects of sdAb supplementation in shrimp diets.

Fisheries and Aquatic Sciences

The sustainability of aquaculture is increasingly threatened by rising ocean temperatures occasioned by the continued prevalence of global warming, which can have severe consequences for fish health and productivity. Fish, as ectothermic organisms, are susceptible to temperature fluctuations and prolonged exposure to extreme temperatures can lead to physiological disruptions, including altered metabolic rates, oxidative stress, and immune suppression, ultimately affecting their growth and reproductive success. In response, several strategies, including dietary supplementation, have been proposed to alleviate temperature stress in aquaculture. One such supplement, gamma (γ)-aminobutyric acid (GABA), a non-proteinogenic amino acid, has garnered attention for its potential to enhance stress resilience in aquatic species. In this review, we examine the physiological responses of fish to temperature stress and evaluate the role of GABA in alleviating non-temperature stress. By synthesizing the available evidence, we aim to highlight the potential of GABA as a dietary supplement to improve the resilience of farmed fish to temperature fluctuations, ultimately contributing to sustainable aquaculture in the face of climate change. GABA acts as an inhibitory neurotransmitter in the central nervous system, promoting relaxation and reducing stress. We not only spotlight GABA’s role in the central nervous system, where it has been shown to modulate stress responses by enhancing antioxidant defenses, improving growth performance, and boosting disease resistance, but also emphasize the limited exploration of its potential to mitigate temperature stress in some aquaculture species, particularly economically important fish like olive flounder. Finally, in this review, we provide additional insights into how GABA might help mitigate temperature stress by identifying factors that may influence its supplementation, thereby laying the groundwork for future research on its use as a potential tool for mitigating temperature stress in aquaculture species.

γ-aminobutyric acid (GABA) is a functional feed additive that may improve growth and stress resilience. The study evaluated the effects of dietary GABA on growth performance and recovery-phase physiological responses after short-term acute thermal exposure in juvenile rainbow trout. Two hundred twenty-five fish (18.9 ± 0.1 g) were fed five diets for 8 weeks: a control diet containing 68 mg/kg (GABA₆₈) and diets with 108 (GABA₁₀₈), 149 (GABA₁₄₉), 183 (GABA₁₈₃), and 218 (GABA₂₁₈) mg/kg GABA. Fish were then subjected to short-term acute thermal exposure (20 °C for 2 h) followed by 2 h recovery at 15 °C. Dietary GABA significantly improved weight gain and specific growth rate, with the provisional model-based dietary GABA level for weight gain estimated to be approximately 198–210 mg/kg diet based on broken-line regression models, and increased feed and protein efficiency (p < 0.05). Fish fed the GABA183 and GABA218 diets had significantly higher plasma cortisol concentrations than those fed GABA68 and GABA108 when averaged across temperature treatments, with a significant temperature × GABA interaction (p < 0.05). During recovery, hepatic hsp70α and hsp90βα expression was significantly lower following 20 °C exposure than in fish maintained at 15 °C, whereas dietary GABA and its interaction with temperature had no significant effects on the stress-related genes analyzed. Dietary GABA improved growth performance and feed utilization; however, cortisol measured at a single recovery time point cannot distinguish a stronger stress response, delayed recovery, or altered cortisol clearance and does not demonstrate improved thermal tolerance or a faster recovery rate.