This study comprehensively analyzed the effects of different cultivation methods (CMs) and densities on the growth of Gracilariopsis lemaneiformis in indoor settings and two representative sea areas, Ailun Bay and Nanri Island, located in the northern and southern parts of China. The findings indicate that horizontal hanging cultivation significantly enhanced macroalgal growth and biomass production in both sites. In contrast, vertical hanging cultivation resulted in significantly lower yields, primarily due to inadequate illumination below certain water depths and epibiont infestation. Moreover, integrated multitrophic aquaculture (IMTA) systems co-cultivated with scallops demonstrated biomass and specific growth rates (SGR) similar to those of horizontal hanging cultivation, and nutrient concentrations in the IMTA areas were lower than those in the scallop monoculture areas. These observations suggest a potential role for G. lemaneiformis in nutrient mitigation. Regarding cultivation density (CD), lower densities were beneficial for higher SGR in both regions, with limited impact on final biomass, suggesting that moderately reducing CD could promote growth and reduce seedling use. Within optimal ranges, light intensity positively correlated with SGR; however, excessive light appeared to induce light-related stress or photoacclimation, as well as pigment reduction, in horizontal hanging cultivation, suggesting adverse effects under high-light conditions. In vertical hanging cultivation, reduced light increased pigment content, likely as an adaptive response to insufficient light, while increased density led to decreased SGR indoors, suggesting that resource competition under high-density conditions may limit SGR. Our research indicates that horizontal hanging cultivation at a lower density (0.15 kg/m) can enhance SGR and reduce seedling use without compromising final biomass, suggesting a potential strategy for improving cultivation efficiency. However, the practical adoption of this strategy should also consider site-specific factors such as seed costs, labor availability, and seasonal risks. This study provides useful information for optimizing seaweed cultivation practices and highlights the importance of adopting ecological and sustainable methods in aquaculture.
Our previous research evaluated two sources of chitosan at dietary inclusion levels of 2 and 4 g/kg and identified 4 g/kg black soldier fly larvae (BSFL)‐derived chitosan as the optimal level of this feed additive, which resulted in higher growth, immune responses and gut health in Macrobrachium rosenbergii . Building on these findings, the present study compared this level of inclusion with a higher level of 6 g/kg under two rearing conditions, individual and communal, to examine dose‐dependent and system‐specific effects on growth performance and immunity. The 60‐day feeding trial comprised four treatments, each in triplicate: prawns fed 4 g/kg BSFL chitosan in an individual system (T1), 6 g/kg BSFL chitosan in an individual system (T2), 4 g/kg BSFL chitosan in a communal system (T3) and 6 g/kg BSFL chitosan in a communal system (T4). Treatment T3 produced the highest values for final weight, weight gain, specific growth rate (SGR), condition factor and length gain, reaching 8.18 g, 477.02%, 1.26%/day, 1.30 and 55.12%, respectively. Overall, prawns fed 6 g/kg chitosan showed reduced growth metrics and condition factor, whereas prawns reared communally showed higher growth performance. Unlike weight‐related traits, length‐related traits showed an interaction between chitosan inclusion level and rearing condition. A separate Poly[d(I:C)] challenge experiment was conducted to assess immunocompetence. Time‐course profiles of relative mRNA expression of antioxidant and immune‐related genes were quantified at 3, 6, 24 and 48 h post‐injection in prawns fed 4 g/kg chitosan for 60 days (chitosan‐supplemented [CS]) and prawns fed the control diet without chitosan (non‐chitosan‐supplemented [NCS]). The sod gene was upregulated at all time points in CS prawns. The cat and proPO genes were upregulated at 24 and 48 h in CS prawns, whereas the inflammatory and stress‐related genes tnf-α and p53 genes peaked at 6 h in NCS prawns. These findings indicate that 4 g/kg dietary BSFL‐derived chitosan is the optimal inclusion level for promoting growth in M. rosenbergii , while increasing the inclusion to an increased level of 6 g/kg dietary chitosan adversely affects growth. The 4 g/kg inclusion also modulated immune‐ and antioxidant‐related gene expression compared with the non‐chitosan control.
Probiotics are increasingly explored as sustainable alternatives to antibiotics in ornamental fish culture due to their potential to enhance growth performance, health, and pigmentation. However, limited information is available on the effects of probiotic supplementation in guppies ( Poecilia reticulata ), a globally important ornamental fish species. This study evaluated the probiotic potential of a strain of Lactocaseibacillus rhamnosus through a combination of in vitro characterization and in vivo feeding trials. The probiotic potential of L. rhamnosus LRS7 was assessed based on its acid tolerance, antibacterial activity against pathogenic bacteria, antimicrobial susceptibility profile, and hemolytic activity. For the feeding trial, L. rhamnosus LRS7 was incorporated into a basal diet at concentrations of 1 × 10 6 (ED1), 1 × 10 8 (ED2), and 1 × 10 10 (ED3) CFU g −1 and fed to male guppy fry for 60 days. Growth performance, feed conversion ratio (FCR), survival, skin coloration, and resistance to Aeromonas hydrophila challenge were evaluated compared to a basal diet with no probiotics. L. rhamnosus LRS7 exhibited favorable probiotic properties, characterized by survival under moderately acidic conditions, broad‐spectrum antagonistic activity against pathogenic bacteria, susceptibility to commonly used antibiotics, and nonhemolytic behavior, indicating its potential as a safe probiotic candidate. Probiotic‐supplemented diets resulted in significantly higher weight and length gain compared to the control diet ( p < 0.05). Fish fed L. rhamnosus at 1 × 10 8 CFU g −1 exhibited the highest weight gain and lowest FCR. Probiotic supplementation significantly affected skin pigmentation in sunset guppies, resulting in altered red, green, and blue (RGB) color profiles indicative of enhanced color quality and saturation. Survival following pathogen challenge increased from 33.3% in the control group to 77.8%–100% in probiotic‐treated groups, although differences were not statistically significant. Overall, the results indicate that supplementation with L. rhamnosus LRS7, which exhibited a favorable safety profile, can enhance growth performance, feed utilization efficiency, disease resistance and coloration in guppies.
As global aquaculture expands to meet the growing protein demand, the industry faces mounting pressure to reduce reliance on conventional protein sources. Identifying alternative protein sources that are environmentally sustainable, resource‐efficient and nutritionally viable is crucial for the future of aquafeed development. In this regard, filamentous fungi have emerged as a promising alternative protein source due to their favourable nutritional profile and sustainable production potential. Although filamentous fungi contain high protein content and can be efficiently cultivated on organic waste materials, they are not yet utilised in commercial aquafeeds. In this study, juvenile rainbow trout ( Oncorhynchus mykiss ) were fed an extruded commercial‐like reference (Ref) diet and four experimental diets where Ref was mixed with 30% biomass of Aspergillus oryzae (AO), Neurospora intermedia (NI), Rhizopus delemar (RD), or Rhizopus oligosporus (RO) grown on thin waste from ethanol production. The fungal diets exhibited nutritional profiles and growth performance comparable to the Ref diet, despite significantly higher feed conversion ratios (FCRs) observed in the AO, NI and RO groups. Dietary digestibility was generally lower in the fungal‐diet groups than in the Ref group, although the digestibility of some amino acids in the AO group did not differ significantly from Ref. Dietary inclusion of fungal biomass induced noticeable shifts in gut microbial composition compared to the Ref diet, with the RO diet resulting in a distinct beta diversity profile. Firmicutes phylum members, including Weissella , Lactobacillus and Bacillus , were significantly more abundant in fish fed the NI, RD and RO diets, respectively. Overall, the evaluated filamentous fungi produced species‐dependent nutritional and microbiota responses in rainbow trout, although further optimisation is required to improve their nutritional value at the tested inclusion level.
This study evaluated the chemical composition, in vitro antibacterial activity, and acute host toxicity in juvenile guppies ( Poecilia reticulata ) of essential oils (EOs) obtained from Schinus terebinthifolia , Citrus limon , and Melaleuca leucadendra . Phytochemical analyses identified limonene (75.7%) as the primary component in C. limon , an atypical chemotype rich in (E)‐nerolidol (97.9%) in M. leucadendra , and a mixture dominated by limonene (86.2%) in S. terebinthifolia . In vitro disk diffusion and microdilution assays against four pathogens ( Aeromonas hydrophila , Streptococcus agalactiae , Vibrio parahaemolyticus , and Listeria monocytogenes ) revealed distinct inhibitory profiles. S. terebinthifolia EO produced the largest inhibition zones against A. hydrophila (36.7 mm) and S. agalactiae (30.4 mm). C. limon EO showed the highest relative inhibitory activity against V. parahaemolyticus (16.2 mm), whereas M. leucadendra EO exhibited the lowest direct growth inhibition across all tested bacteria. In 4‐h acute toxicity assays using healthy juvenile P. reticulata , the median lethal concentrations (LC50) were 29.07 mg/L for S. terebinthifolia , 32.41 mg/L for M. leucadendra , and 84.84 mg/L for C. limon . Bacterial minimum inhibitory concentrations (MIC: 1950–7810 mg/L) exceeded the 4‐h acute lethal thresholds of the fish by up to 268‐fold. Consequently, the calculated in vitro therapeutic indices (TI = host LC50/bacterial MIC) were exceptionally low across all oil–pathogen pairs (0.0037–0.0435), remaining far below the threshold of unity (TI ≥ 1.0) required for safety. These findings demonstrate that unformulated EOs trigger acute lethality in P. reticulata at concentrations well below their antibacterial thresholds, underscoring the need for specialized encapsulation or targeted delivery systems before considering aquatic immersion treatments.
