Combining feeding appendage morphology and behavioural observation of the motion pattern of the feeding appendages clarified many aspects underlying the feeding processes of the giant freshwater prawn (Macrobrachium rosenbergii) and the marine whiteleg shrimp (Litopenaeus vannamei) in aquaria. The food intake behaviour was video recorded during eating pellet food, pieces of fresh squid and fish. While M. rosenbergii took pellet one by one, L. vannamei picked up many pellets at one time and held them at the mouth with the 3rd maxilliped endopods and the 1st walking legs. Both species used the right chelate walking legs rather than the left walking legs to pick up the food. The 3rd walking legs of L. vannamei were longest and heaviest among the chelate walking legs but their major role was not for feeding but for feeding contests aggression. While M. rosenbergii easily crunched pellets by the mandibles, L. vannamei did not crunch pellets due to the softer and not strong mandibles and frequently spat out them, indicating that the present hard pellets are not suitable for L. vannamei. Both species kept a piece of elastic fresh squid or fish flesh at the mouth and tore the food into small pieces with the help of repeated pulling down motion of the 3rd maxilliped endopods. However, the mandible teeth of the two spices were not sharp enough to gnaw off the fibrous muscle in one bite. The 2nd and 3rd maxilliped endopods were used for holding food at the mouth and did not contribute to mastication of food. The 2nd and 3rd maxilliped exopods exhibited the horizontal fanning motion, which a unidirectional water flow moving backwards in the gill chamber (visualized with milk). The maxilliped exopods were found to contribute not to feeding but ventilation. Based on the results obtained, development of softer pellets was recommended for L. vannamei.

The majority of shrimp producers utilize probiotics derived from terrestrial sources as part of their aquaculture management. The beneficial effects of terrestrial probiotics on shrimp may be affected due to environmental differences between the cultivated species and the source of the probiotics. To ensure maximum effects on the host, it is essential to use probionts derived from the host or the environment of the cultured organism. Consequently, the objective of this study was to isolate and characterize potential probionts from brackishwater by enriching the water with organic sources containing a high ratio of carbon to nitrogen (C:N). Six 10-li containers were filled with brackishwater from an estuary for a mesocosm experiment. To stimulate bacterial growth, water was enriched with either molasses or brown sugar at a C:N ratio of 15. After twenty days, all heterotrophic bacteria in the enriched water were enumerated. The in vitro antagonistic activities of distinct bacterial colonies against Vibrio harveyi, a crustacean pathogen, were evaluated on fresh Nutrient Agar plates containing 1% sodium chloride. There were 10 bacterial isolates with in vitro antibacterial activity. These bacterial isolates are categorized as belonging to the putative genera Acinetobacter, Pseudomonas, Sphingobium, and Rheinheimera. The implications of this study suggest that enriching brackishwater with organic carbon sources at high C:N ratios may increase the likelihood of isolating and developing potential probionts for shrimp aquaculture.

Motile aeromonad septicemia (MAS), caused by the Aeromonas species, has been a serious problem in fish health management, particularly in Nile tilapia (Oreochromis niloticus). This study characterized an Aeromonas species isolated from farmed tilapia fingerlings in Binangonan, Rizal, Philippines, and tested for its pathogenicity in tank trials. The isolate, designated as Aeromonas veronii DFR01 (Diseased Fish Rizal), was identified based on 16S rRNA phylogenetic analysis, 16S rRNA homology, and MALDI-TOF mass spectrometry. Its biochemical profile was generated from API and Biolog Gen III systems. A median lethal dose of A. veronii DFR01 was determined to be 10⁷ CFU/mL in tank trials and was utilized as a whole-cell inactivated antigen for oral vaccine development. The immunized tilapia fingerlings produced elevated levels of immunoglobulin M (IgM) in the blood as determined by an enzyme-linked immunosorbent assay (ELISA). There was a significant increase in IgM levels 14 days post-vaccination. A quantitative polymerase chain reaction (qPCR) showed increasing levels of IgM gene expression after vaccination until 38 days of culture. Vaccinated fish showed 25–35% cumulative mortality after the challenge, while non-vaccinated-challenged fish showed 75% mortality. The findings of this research suggest that the fish oral vaccine may prove beneficial for farmed tilapia populations. The vaccine elicited improved immune responses in the fish and resulted in higher survival rates.

Freshwater prawns of the genus Macrobrachium are among the most valuable cultured aquatic species in the world. The systematic study of Macrobrachium species in the Philippines has often been based on morphological trait assessment. Here, we combined morphology and molecular approaches to study the presence and actual distribution of Macrobrachium species along the Cairawan River in Laua-an, Antique Province, Panay Island. Using morphological characteristics, we identified 11 Macrobrachium species, the highest number of species reported from a single river. Molecular results based on the cytochrome oxidase subunit I (COI) mitochondrial DNA (mtDNA) sequences confirmed the morphological identification. The analysis revealed eight major clades with 19 distinct haplotypes within the species. Our results provide information on the identification of Macrobrachium species inhabiting the Cairawan River. The baseline information can be helpful for future genetic studies involving freshwater prawns with potential use in aquaculture. It can provide scientific data to facilitate the formulation of selective breeding plans and direct governance policies in freshwater prawn resource conservation and management in the Philippines.

Understanding the genetic diversity and population structure of anguillid eels is crucial for effective management. In this study, we used the mitochondrial DNA (mtDNA) D-loop marker to identify anguillid glass eels and assessed their genetic diversity across six sampling sites spanning three Southeast Asian countries. We also examined the population structures of Anguilla marmorata and A. celebesensis. We validated nine distinct species and subspecies of anguillid eels from 465 specimens collected in Indonesia (n = 246), the Philippines (n = 119), and Vietnam (n = 100). High gene diversities were observed across the species, ranging from 0.979 (A. celebesensis) to 1.000 (A. bicolor bicolor, A. marmorata, and A. interioris). Correspondingly, nucleotide diversity values were relatively low, varying from 0.036 (A. marmorata) to 0.057 (A. interioris). A. marmorata (n = 162) displayed a broad distribution, being observed across all six sites, with a significant yet low average fixation index of 0.05755. Pairwise comparisons of FST values between Cimandiri and other locations (except for Cagayan) were relatively high and statistically significant (p < 0.01), indicating significant genetic differentiation of Cimandiri samples compared to most locations in this study. On the other hand, A. celebesensis (n = 110), exhibited a non-significant and low fixation index (0.007), indicating no genetic differentiation in samples from Poso and Poigar Rivers, Indonesia. Our findings highlight the essential need for coordinated management strategies among regions that share common stocks. Additionally, this study underscores the efficacy of the mtDNA D-loop in precisely identifying glass eel species/subspecies and elucidating the genetic diversity and population structure of tropical anguillid eels.

The sandfish Holothuria (Metriatyla) scabra, is a high-value tropical sea cucumber harvested from wild stocks for over four centuries in multi-species fisheries across its Indo-Pacific distribution, for the global bêche-de-mer (BDM) trade. Within Southeast Asia, the Philippines is an important centre of the BDM trade, however overharvesting and largely open fishery management have resulted in declining catch volumes. Sandfish mariculture has been developed to supplement BDM supply and assist restocking efforts; however, it is heavily reliant on wild populations for broodstock supply. Consequently, to inform fishery, mariculture, germplasm and translocation management policies for both wild and captive resources, a high-resolution genomic audit of 16 wild sandfish populations was conducted, employing a proven genotyping-by-sequencing approach for this species (DArTseq). Genomic data (8,266 selectively-neutral and 117 putatively-adaptive SNPs) were used to assess fine-scale genetic structure, diversity, relatedness, population connectivity and local adaptation at both broad (biogeographic region) and local (within-biogeographic region) scales. An independent hydrodynamic particle dispersal model was also used to assess population connectivity. The overall pattern of population differentiation at the country level for H. scabra in the Philippines is complex, with nine genetic stocks and respective management units delineated across 5 biogeographic regions: (1) Celebes Sea, (2) North and (3) South Philippine Seas, (4) South China and Internal Seas and (5) Sulu Sea. Genetic connectivity is highest within proximate marine biogeographic regions (mean F_st=0.016), with greater separation evident between geographically distant sites (F_st range=0.041–0.045). Signatures of local adaptation were detected among six biogeographic regions, with genetic bottlenecks at 5 sites, particularly within historically heavily-exploited locations in the western and central Philippines. Genetic structure is influenced by geographic distance, larval dispersal capacity, species-specific larval development and settlement attributes, variable ocean current-mediated gene flow, source and sink location geography and habitat heterogeneity across the archipelago. Data reported here will inform accurate and sustainable fishery regulation, conservation of genetic diversity, direct broodstock sourcing for mariculture and guide restocking interventions across the Philippines.

A fixed off-bottom Kappaphycus striatus var. sacol farm was monitored for 12 months (June 2019 to May 2020) and the monthly incidence of disease and pests was recorded. Meteorological information in situ, from the nearest synoptic station and online data were collected to determine the relationships between temporal environmental changes and the incidence of seaweed health problems. The results showed that “ice-ice” disease (IID) was observed in dry months (i.e., from February to April 2020) and was significantly influenced by increased irradiance, salinity, sea surface temperature, and wind speed (p=0.004‒0.030). Also, the IID incidence was positively affected by reduced precipitation, storm surface run-off, water current speed, and inorganic nutrient (nitrite and ammonia) levels (p=0.002‒0.019). In comparison, epiphytic filamentous algae (EFA) were observed in wet months (i.e., from September to December 2019), with incidence varying from low to very high (≤25–100%) as the culture progressed. EFA incidence was significantly influenced by reduced salinity and increased storm surface run-off and inorganic nutrient (nitrate and ammonia) levels (p=0.006‒0.040). An intense tropical cyclone struck the farming area in December 2019, resulting in partial die-offs of farmed seaweed. Such seaweed health problems are expected to become more prevalent in the coming years as weather disturbances brought about by changing weather patterns become more frequent and intense. Hence, mitigation and preventative approaches must be fully considered to sustain the industry’s growth while protecting the livelihoods of many coastal communities dependent on seaweed farming.

Since the first occurrence of White Spot Disease (WSD) in 1992, it is still listed as one of the crustacean diseases by the World Organisation for Animal Health in 2022. Horizontal transmission in co-culture systems is one of the usual modes in the spread of the disease. WSD outbreak was recorded during the experimental run of the co-culture of black tiger prawn (Penaeus monodon) and sandfish (Holothuria scabra) in the grow-out phase. In this study, artificial infection through two cohabitation experiments were conducted to determine if H. scabra is a potential non-crustacean vector or reservoir of WSSV. Samples were checked using one-step and nested PCR for increased readout sensitivity of virus infection to investigate the horizontal transmission between prawn and sandfish. During the first cohabitation (5 days) where WSSV (+) prawn were cohabited with WSSV (-) sandfish, 100% of the prawn were one-step PCR positive for WSSV while 100% of the sandfish were nested PCR positive. Subsequently, WSSV (+) sandfish from the first cohabitation were transferred to another tank to be cohabited with WSSV (-) prawn. Sampling of both prawn and sandfish was done every 6 days post-infection (dpi). At 6 to 18 dpi, prawn and sandfish were nested PCR positive. At 25 dpi, there were no prawns left due to mortality and 1 of the 3 remaining sandfish was nested PCR positive. Based on the results, it elucidates the ability of sandfish to bioaccumulate the viral particles when cohabited with WSSV (+) prawn. Results suggest that WSSV is viable in the sandfish confirming its potential as a vector or reservoir due to the consistent nested PCR positive results of the prawn during the second cohabitation. Hence, it can be inferred that sandfish can be a potential non-crustacean vector or reservoir of WSSV for a limited period of time.

We announce the complete genome sequence of Vibrio parahaemolyticus strain PH1273. This strain was collected from a Penaeus vannamei pond in the Philippines in 2015. Genome analysis revealed that it lacks the gene pirAB responsible for causing acute hepatopancreatic necrosis disease but encode multiple secretion systems and the associated effectors.