Porphyridium cruentum–enriched Artemia enhances survival, growth, and viral resilience of glass eels (Anguilla bicolor bicolor) under endemic Anguillid herpesvirus-1 conditions

Background and Aim: The tropical eel Anguilla bicolor bicolor is a valuable aquaculture commodity; however, the survival of glass eels during the early nursery stage remains low due to nutritional limitations and vulnerability to viral infections, especially Anguillid herpesvirus-1 (AngHV-1). Using microalgae to enrich live feed has been suggested as a strategy to enhance larval nutrition and resilience in endemic disease conditions. This study examined the effects of Artemia enriched with the red microalga Porphyridium cruentum on the nutritional quality of live feed, survival and growth of glass eels, intestinal structure, water quality, bacterial dynamics, and AngHV-1 infection status under hatchery-like conditions. Materials and Methods: A completely randomized design with seven treatments was employed: an unenriched control and six enrichment combinations based on P. cruentum cell density and enrichment duration (3 × 10⁵ cells/mL for 6 h; 3 × 10⁵ cells/mL for 12 h; 6 × 10⁵ cells/mL for 6 h; 6 × 10⁵ cells/mL for 12 h; 9 × 10⁵ cells/mL for 6 h; and 9 × 10⁵ cells/mL for 12 h), each with three replicates. Glass eels (0.12 ± 0.01 g; 4.96 ± 0.09 cm) were stocked at 90 fish per tank in 70-L containers and reared for 60 days, fed exclusively with either enriched or unenriched Artemia. Evaluations included the proximate composition of enriched Artemia, survival rate, growth performance, intestinal villus morphometry, water quality parameters, total heterotrophic bacterial counts, and the presence of AngHV-1 verified through conventional polymerase chain reaction. Results: Enrichment substantially enhanced the nutritional profile of Artemia, increasing crude protein to 61.48% and lipid content to 9.98% on a dry matter basis. The treatment with P. cruentum at 6 × 10⁵ cells/mL for 6 h yielded the highest survival rate (60.74 ± 3.9%) and specific growth rate (1.11 ± 0.1%/day), both significantly higher than those in the control and other treatments (p < 0.05). Intestinal villus length and surface area showed no significant differences among treatments (p > 0.05). Water quality remained within suitable ranges for glass eel culture, and bacterial counts, although slightly higher in enriched treatments, stayed below harmful thresholds. AngHV-1 was detected in all groups, but the enriched treatment at 6 × 10⁵ cells/mL for 6 h exhibited the faintest viral DNA band, indicating a reduction in apparent viral signal. Conclusion: Short-term enrichment of Artemia with P. cruentum, especially at 6 × 10⁵ cells/mL for 6 h, notably improves the survival and growth performance of A. bicolor bicolor glass eels without harming intestinal morphology or water quality. The lower AngHV-1 polymerase chain reaction signal indicates a possible role of nutritionally enriched live feed in boosting host resilience and reducing viral activity under endemic infection conditions. This enrichment method offers a practical and non-drug approach to enhance early-stage eel aquaculture performance. Keywords: Anguilla bicolor bicolor, Anguillid herpesvirus-1, Artemia enrichment, eel aquaculture, glass eel survival, Porphyridium cruentum, tropical eel culture, viral resilience.