Use of a filamentous green alga (Chaetomorpha sp.) and microsnail (Stenothyra sp.) as feed at an early stage of intensive aquaculture promotes growth performance, artificial feed efficiency, and profitability of giant tiger prawn (Penaeus monodon).

With the worldwide demand for tropical penaeid prawn increasing in recent decades, more research on shrimp culture methods is needed to enhance efficiency and profitability for shrimp farmers. The objective of this study was to develop a technique to boost the productivity, feed efficiency, and profitability of the giant tiger prawn (Penaeus monodon). To accomplish this, a novel culture setup was established in which two benthic organisms, a filamentous green alga (Chaetomorpha sp.) and a microsnail (Stenothyra sp.), were propagated together with P. monodon post-larvae during an early culture stage and then offered to shrimp as supplementary live feeds in intensive aquaculture ponds. For the experiment, shrimp post-larvae (density: approximately 33 individuals m-2) were cultured in outdoor concrete ponds (9 × 9 × 1.2 m) under either control (fed only artificial feed, n = 3) or experimental (fed artificial feed and benthic organisms, n = 3) conditions until they reached marketable size (15 weeks). Apparent green algae consumption was 6.81 kg (8.4% green alga to total feed consumption), whereas microsnail consumption was 1.96 kg (2.4% microsnail to total feed consumption). Compared with the control group of giant tiger prawn, the experimental group showed significantly higher productivity (total number of shrimp produced: 118%; total shrimp production: 133%), feed efficiency (feed conversion ratio of artificial shrimp feed: 89%), and profitability (shrimp sales: 139%; balance between shrimp sales and costs: 146%), while labor and financial costs were kept minimal. These results can be explained by the enhanced growth of shrimp at the early stages of culture. The techniques developed in this study will help to advance the efficiency of intensive aquaculture operations for giant tiger prawn and also improve profitability for shrimp farmers.

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

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.

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.

Occurrence, molecular characterization, and antimicrobial susceptibility of Aeromonas spp. in marine species of shrimps cultured at inland low salinity ponds.

We aimed to document the risk of Aeromonas spp. in marine shrimp species cultured in inland low salinity ponds in Thailand. In 14 of 18 shrimp samples retrieved from inland grow-up ponds, Aeromonas spp. were detected at ranges from 4667 to 1,500,000 CFU/g body weight. The phylogenetic tree constructed with the gyrB and cpn60 concatenated sequences indicated that the 87 isolates consisted of Aeromonas veronii (70%), Aeromonas aquariorum (18%), Aeromonas caviae (7%), Aeromonas jandaei (2%), and Aeromonas schubertii (2%). The potential virulence of the isolates was examined by phenotypic and PCR assays. Hemolytic activity and the extracellular activity of lipase, DNase, and gelatinase were observed in most isolates (94-99%). PCR revealed the presence of 9 genes related to virulence in the 87 isolates: act (75%), aer (74%), alt (30%), ast (1%), ascV (34%), aexT (24%), fla (92%), ela (34%), and lip (24%). The susceptibility profiles to 14 antimicrobial agents of isolates were typical for the genus, but resistance to cefotaxime, a third-generation cephalosporin, and imipenem were found in two A. aquariorum and in three A. veronii isolates, respectively. These resistances were confirmed by determining minimum inhibitory concentrations. Our results indicate that the microbiological risk posed by Aeromonas should be considered for marine shrimp species that are cultured in low-salinity ponds. These shrimps may also be a vehicle for the transfer of different genotypes of Aeromonas and antibiotic-resistant determinants to regions worldwide through trade.

Novel member of the PAR domain bZIP gene family isolated from Pacific oyster, Crassostrea gigas.

A cDNA encoding the first mollusk member of the PAR subfamily of bZIP transcription factors has been characterized in the Pacific oyster, Crassostrea gigas. The sequence of the cDNA predicts a protein of 260 amino acids that has 41-50% identity with the PAR domain, 72-79% identity with the basic DNA-binding domain and 34-56% identity with the leucine zipper domain of other members of the PAR subfamily. Polymerase chain reaction with reverse transcription indicates that this gene is expressed during developmental stages from an unfertilized egg to a juvenile. It was demonstrated by northern hybridization that the gene is also expressed on several adult tissues. The identification of a novel member of the PAR subfamily bZIP genes in mollusks may help to identify common functions that have been conserved through evolution and to elucidate evolutionary relationships within this subfamily of proteins.

CREB in the pond snail Lymnaea stagnalis: cloning, gene expression, and function in identifiable neurons of the central nervous system.

The pond snail Lymnaea stagnalis is an excellent model system in which to study the neuronal and molecular substrates of associative learning and its consolidation into long-term memory. Until now, the presence of cyclic AMP (cAMP)-responsive element binding protein (CREB), which is believed to be a necessary component in the process of a learned behavior that is consolidated into long-term memory, has only been assumed in Lymnaea neurons. We therefore cloned and analyzed the cDNA sequences of homologues of CREB1 and CREB2 and determined the presence of these mRNAs in identifiable neurons of the central nervous system (CNS) of L. stagnalis. The deduced amino acid sequence of Lymnaea CREB1 is homologous to transcriptional activators, mammalian CREB1 and Aplysia CREB1a, in the C-terminal DNA binding (bZIP) and phosphorylation domains, whereas the deduced amino acid sequence of Lymnaea CREB2 is homologous to transcriptional repressors, human CREB2, mouse activating transcription factor-4, and Aplysia CREB2 in the bZIP domain. In situ hybridization revealed that only a relatively few neurons showed strongly positive signals for Lymnaea CREB1 mRNA, whereas all the neurons in the CNS contained Lymnaea CREB2 mRNA. Using one of the neurons (the cerebral giant cell) containing Lymnaea CREB1 mRNA, we showed that the injection of a CRE oligonucleotide inhibited a cAMP-induced, long-lasting synaptic plasticity. We therefore conclude that CREBs are present in Lymnaea neurons and may function as necessary players in behavioral plasticity.