Southeast Asian Fisheries Development Center

Hypnea is a cosmopolitan genus of red seaweeds and an important source of carrageenan worldwide. However, Hypnea species remain largely unutilized in seaweed aquaculture in the Philippines. This study aimed to evaluate the growth performance and carrageenan properties of an indigenous, unexploited Hypnea sp. collected from Panay Island and to compare them with those of the commercially cultivated Kappaphycus striatus. In a field cultivation experiment, Hypnea sp. showed significantly higher biomass (145.1 ± 53.7 g) than K. striatus (92.9 ± 10.3 g) up to day 28 (p < 0.001), while no significant difference was observed at days 36 and 43. The final yields were 181.0 ± 68.4 g for Hypnea sp. and 191.1 ± 33.0 g for K. striatus (p > 0.05). Semi-refined carrageenan extracted from the cultured Hypnea sp. exhibited gel-forming capacity, suggesting the presence of κ-carrageenan. However, both the viscosity and gel strength of Hypnea sp. (9.52 ± 3.53 cP; 148 ± 41.6 g cm⁻2) were significantly lower in K. striatus (70.9 ± 49.4 cP; 456 ± 201 g cm⁻2) (p < 0.001), indicating that Hypnea sp. possesses distinct carrageenan properties from conventional commercial seaweed. Although further development of carrageenan-based products tailored to its unique properties will be required for commercial utilization, these findings highlight the potential of Hypnea sp. as a candidate seaweed for aquaculture in the Philippines.

Freshwater biodiversity is declining at a pace that outstrips the capacity of existing monitoring approaches both in temporal and spatial dimensions, highlighting the urgent need for rapid and scalable assessment and attribution of biodiversity states and changes. Here we present a global assessment and unified analysis of riverine fish biodiversity using environmental DNA collected from 1,818 sites across 113 river systems spanning 5 continents. We quantified species richness, functional redundancy, phylogenetic diversity and genetic sequence diversity, and related them to drainage characteristics. Our results showed that environmental DNA effectively captured global patterns of multi-faceted riverine fish biodiversity and disentangled the roles of climate and different aspects of human activities in shaping biodiversity-area relationships. The accumulation of biodiversity with catchment area was consistently enhanced in warmer climates, while human activities weakened this scaling. Further, species richness, functional and genetic sequence diversity exhibited stronger negative responses to human activities in larger catchments. In contrast, phylogenetic diversity was negatively affected by human activities, yet this effect diminished as catchment area increased, highlighting the facet-dependent nature of biodiversity responses to environmental gradients and catchment characteristics. Our findings demonstrate the power of environmental-DNA-based datasets for harmonized, multi-faceted biodiversity assessments, offering a scalable approach for detecting and attributing biodiversity change and informing conservation strategies under accelerating global change.

This study examined maternal genetic diversity and population structure of the giant mottled eel (Anguilla marmorata) in selected river systems in the Philippines and Indonesia using mitochondrial COI sequences. Thirty-nine individuals were sampled from the Cagayan River, Philippines, and the Poso and Telaga Waja/Karangasem rivers, Indonesia. Thirteen haplotypes and 32 polymorphic sites were identified, with moderate haplotype diversity (Hd = 0.623) and low nucleotide diversity (π = 0.00330). Hap_2 was shared among all populations and represented 61.5% of individuals. Tajima's D was significantly negative in both Indonesian populations, and Fu's Fs was strongly negative in INKA, indicating mitochondrial patterns compatible with recent demographic expansion. Phylogenetic and haplotype network analyses showed broad maternal lineage sharing and weak geographic structuring. Pairwise FST values indicated low but significant differentiation between PLCG and both Indonesian populations, whereas INPS and INKA showed no significant differentiation. AMOVA attributed 92.14% of molecular variation to within-population variation, while differentiation between Philippine and Indonesian regional groups was not significant. Overall, the results indicate broad maternal lineage sharing with weak geographic differentiation and provide baseline information for regional genetic monitoring of A. marmorata.

Abstract Spiny lobsters, Panulirus ornatus , are a highly valued crustacean worldwide, with strong demand and high prices making it important for fisheries and aquaculture economies. This study examined the effects of shelter types and feeding rates on rearing performance (which includes growth in weight and carapace length, survival, moulting frequency, shelter preference and feeding behaviour) in early juvenile spiny lobster, P. ornatus in two subsequent tank experiments. In experiment 1, groups of five juveniles (approx. 16 g) were reared separately in replicated tanks (200 litres) with different shelter types (bundled nets vs pipes vs no shelter as control). After 60 days, survival was higher in the bundled net treatment (73%) than in the pipe treatment (67%) and control (33%). However, survival and other rearing performance parameters did not differ significantly among shelter types ( ). In experiment 2, shelter preference among early juveniles (<1 g) were further tested in rectangular tanks (20 litres) with both shelter type (bundled nets and stacked pipes) provided. In addition, different feeding rates using fresh mussel meat were tested: FR10, FR20 and FR30, corresponding to 10, 20 and 30% of mean body weight per day. Results showed that young lobsters strongly preferred bundled net shelters (80% occupancy) vs pipes (20%). Feeding rate significantly affected growth, with FR30 resulting in the highest gain in weight and carapace length. There was a strong positive correlation between mean body weight and daily feed consumption ( ). Nocturnal feeding behaviour was validated, as lobsters significantly consumed more food at night (81%) than during the day (69%) ( ). These results confirmed the importance of providing complex shelters, like bundled nets and optimising feeding regimes (30% of body weight per day, with a higher proportion at night) for improving productivity in the nursery rearing of spiny lobsters.

Restocking and mariculture of hatchery-bred sandfish Holothuria scabra are practiced in some countries to restore depleting wild populations and increase the global dried trepang or beche-de-mer supply. However, releasing cultured juveniles into the wild often results in slow growth and high predation mortalities, which may be related to their ontogenetic level of chemosensory ability to detect food and avoid predators. In a series of experiments using two-chambered aquaria, this study examined the preference responses (e.g., attraction, avoidance, or stationary) of hatchery-bred sandfish juveniles when presented with odors from predators (crab and fish), food (periphyton and formulated feed), combinations of odors, or the absence of odors (i.e., seawater only). Two groups were tested: small-sized sandfish (3–5 g, 4 months old) and medium-sized sandfish (15–20 g, 7 months old). Results showed that sandfish, overall, exhibited the lowest preference for predator odors, tending to remain stationary or select chambers either with seawater only or with food odors. When presented with conflicting predator and food odors, sandfish (particularly the small-sized group) showed a pronounced preference to be stationary, instead of being attracted to or avoiding any chemical odors. These results indicate that sandfish juveniles can detect and discriminate among chemical odors, with responsiveness and behavioral patterns varying across ontogenetic stages, sizes, and rearing histories. These findings provide essential insights that may improve husbandry protocols and optimize sandfish productivity in aquaculture or restocking operations.