Kaoru Hamano

Ecological and Morphological Profile of Floating Spherical Cladophora socialis Aggregations in Central Thailand

The unique beauty of spherical aggregation forming algae has attracted much attention from both the scientific and lay communities. Several aegagropilous seaweeds have been identified to date, including the plants of genus Cladophora and Chaetomorpha. However, this phenomenon remains poorly understood. In July 2013, a mass occurrence of spherical Cladophora aggregations was observed in a salt field reservoir in Central Thailand. The aims of the present study were to describe the habitat of the spherical aggregations and confirm the species. We performed a field survey, internal and external morphological observations, pyrenoid ultrastructure observations, and molecular sequence analysis. Floating spherical Cladophora aggregations (1–8 cm in diameter) were observed in an area ~560 m2, on the downwind side of the reservoir where there was water movement. Individual filaments in the aggregations were entangled in each other; consequently, branches growing in different directions were observed within a clump. We suggest that water movement and morphological characteristics promote the formation of spherical aggregations in this species. The molecular sequencing results revealed that the study species was highly homologous to both C. socialis and C. coelothrix. However, the diameter of the apical cells in the study species was less than that of C. coelothrix. The pyrenoid ultrastructure was more consistent with that of C. socialis. We conclude that the study species is C. socialis. This first record of spherical aggregations in this species advances our understanding of these formations. However, further detailed physical measurements are required to fully elucidate the mechanism behind these spherical formations.

Immunostimulation and yellow head virus (YHV) disease resistance induced by a lignin-based pulping by-product in black tiger shrimp (Penaeus monodon Linn.)

ABSTRACT Yellow head virus (YHV) is classified as one of the most serious pathogens causing a harmful disease in many penaeids, especially black tiger shrimp (Penaeus monodon), with high economic loss. To determine a potent and practical prophylactic strategy for controlling this disease, the toxicity of the by‐product kraft lignin and its ability to control severe YHV infection were investigated in juvenile black tiger shrimp (15.9 ± 1.2 g body weight). The median lethal dosage at 96 h (96‐hrs LD50) of lignin in shrimp was 297 mg/L. Lignin was further added to shrimp diets via top‐dressing to assess its ability to elicit immune stimulation activity. At 14 days after feeding, shrimp fed 1, 3, 5 and 10 g of lignin/kg of diet exhibited significantly higher levels of phagocytic activity (PA) than the control group (P < 0.05). However, differences in total hemocyte count among treatments were not significant during the experimental period (P > 0.05). Additionally, lignin supplementation at 1‐10 g/kg for 14 days failed to protect experimental shrimp against YHV infection. The antiviral activity of lignin against YHV in black tiger shrimp was notable in vitro because compared to control shrimp (96.7 ± 5.8%; P < 0.05), shrimp injected with a pre‐incubated solution of YHV and lignin at 1, 5, 10 and 20 mg/L exhibited significantly lower mortality rates, 23.3 ± 5.8, 16.7 ± 5.8, 23.3 ± 5.8, and 20.0 ± 0.0%, respectively, after a lethal dose of YHV at 14–20 days after injection. These potent effects were clearly supported and confirmed by histopathological and RT‐PCR analyses. Based on these results, the pulping by‐product kraft lignin efficiently inhibits YHV infection in black tiger shrimp. This information will facilitate the development of practical methods to control yellow head disease in the marine shrimp culture industry. HighlightsThe median lethal dosage at 96 h (96‐hrs LD50) of kraft lignin in Penaeus monodon (15.9 ± 1.2 g) was 297 mg/L.Application of kraft lignin 1–10 g/kg diets for 14 days significantly enhanced phagocytic activity in shrimp hemocytes.Lignin supplementation at 1‐10 g/kg diet for 14 days failed to protect experimental shrimp against YHV infection.Immersion 1‐20 mg lignin/L with YHV for 2 h strongly inhibit and effectively protect shrimp from YHV infection.