The use of natural immunostimulants as alternatives to antibiotics has gained attention in aquaculture to mitigate disease impacts. In this study, we evaluated fucoidan extracted from giant bull kelp (Durvillaea potatorum) as a dietary additive in black tiger shrimp (Penaeus monodon). Four experimental diets containing increasing levels of fucoidan (0, 1.0, 2.5, and 5.0 g kg⁻¹ diet) were tested for their effects on growth, non-specific immune parameters, and survival against white spot syndrome virus (WSSV) and acute hepatopancreatic necrosis disease (AHPND)-causing Vibrio parahaemolyticus. After 30 days of feeding, fucoidan supplementation did not adversely affect shrimp growth or culture survival, even at the highest inclusion level (5 g kg⁻¹). Non-specific immunological indices, including total hemocyte count (THC), differential hemocyte count (DHC), phenoloxidase (PO) activity, plasma total protein (PTP), and plasma agglutination titer (PAT), were enhanced by fucoidan supplementation, with improvements observed even at 1 g kg⁻¹ relative to the control group. Activation of non-specific immunity translated into increased resistance against WSSV and AHPND, with the highest survival recorded in shrimp fed 5 g kg⁻¹ fucoidan, followed by 2.5 g kg⁻¹. In comparison, similar survival rates against WSSV and AHPND were observed in the unsupplemented control and 1 g kg⁻¹ fucoidan. Overall, this study demonstrates that dietary inclusion of D. potatorum fucoidan at 5 g kg⁻¹ effectively enhances immune responses and disease resistance in P. monodon without negatively impacting growth performance, highlighting its potential as a functional feed additive in shrimp aquaculture.

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.

Vibriosis, a bacterial disease, is considered a significant threat to the sustainability and economic viability of shrimp production. The present study evaluated the application of a predatory bacterium to control the population growth of pathogenic Vibrios in Pacific whiteleg shrimp (Penaeus vannamei). The predatory bacterium was identified as Bacteriovorax sp. OP175948.1 based on the 16S rRNA sequence. The Vibrio-inhibitory activity of Bacteriovorax sp. was evaluated using two independent trials with P. vannamei, exposed to two pathogenic Vibrios, including Vibrio parahaemolyticus and Vibrio harveyi. Each trial was conducted in five treatments, including a negative control, a positive control, and a treatment with Bacteriovorax sp. applied at 10², 10⁴, and 10⁶ plaque-forming units mL⁻¹ (PFU mL⁻¹). Results indicated that shrimp infected with V. parahaemolyticus and V. harveyi, and then treated with Bacteriovorax, showed a 6-fold increase in survival for V. parahaemolyticus and a 3-fold increase for V. harveyi, relative to the control. The shrimp treated with 10⁴ to 10⁶ Bacteriovorax sp. improved survival associated with a significant decline in Vibrio spp. counts in the shrimp tissues and rearing water. The Bacteriovorax sp. should be used as a practical strategy to prevent Vibrio-associated mortalities in P. vannamei aquaculture.

Optimizing stocking density is necessary to maximize the production efficiency of farmed fish. This study examined the effect of stocking density on the growth performance of the Pacific shortfin eel Anguilla bicolor pacifica reared in outdoor tank conditions. Glass eels (0.72 ± 0.03 g mean body weight [BW]) were stocked at 50 and 100 individuals m⁻² in 6 4-m² outdoor tanks with a flow-through system set up in triplicate. Eels were individually measured for total length and BW, followed by blood sampling at the end of the 286-d trial. Glass eels stocked at a density of 50 m⁻² exhibited significantly higher specific growth rate, feed efficiency, and protein efficiency ratio. However, survival, final BW, percent weight gain, biomass, biometric indices, and Fulton’s condition factor were not significantly different between density groups. Although size class distribution was not significantly affected by stocking density, a higher proportion of larger eels (> 50 g) was evident at low stocking density. The coefficients of variation in both length and weight and in skewness were likewise slightly reduced at low stocking density. In contrast, high stocking density resulted in significantly elevated levels of serum total protein. Partial costs-and-returns analysis showed that 50 m⁻² density resulted in higher net profit and profit index. These results suggest that under outdoor tank conditions, a stocking density of 50 m−2 will result in higher growth rate and feed utilization, less size variation, better physiological condition, and higher net returns for the culture of A. bicolor pacifica.

In aquaculture-based stock enhancement, releasing juveniles at larger sizes can increase their chances of survival. Moreover, on-site (or within the release area) nursery rearing or intermediate culture of hatchery-bred stocks is important for acclimatization prior to release. In the Philippines, the prospect for tiger shrimp (Penaeus monodon Fabricius 1798) intermediate culture was evaluated in the New Washington Estuary (NWE), Aklan, Philippines. Locally sourced postlarval (PL₁₃) tiger shrimp P. monodon were reared in a temporary netted pen within a disused pond with mangroves. Serendipitously, storm events occurred during a couple of our rearing trials (Runs 1 and 2). This provided us with the unique opportunity to assess the effects of rainstorms on the cultured PL using morphological and environmental data, measured before, during, and after storm events. Notably for Run 1, four distinct phases were identified: Acclimatization phase (ACCL), Stable phase (STBL), Storm phase (STRM), and Recovery phase (RCVR). Culture performance indicators like growth, survival/mortality rate, and condition factor (CF) revealed significant differences among phases. Mortality rate of − 6.4% d⁻¹, growth rate of 9.9% d⁻¹, and low CF (0.24) of shrimp in the initial first week (D1–D9 of ACCL before the storm) were associated with stress and density stabilization (from 325 m⁻² to 178 m⁻²). During STBL (D10–D18), stock conditions improved (growth: 20% d⁻¹, mortality: − 0.17% d⁻¹, CF: 0.49). However, this abruptly degraded during STRM (D20–D28) with negative growth rate (− 9.7% d⁻¹), high mortality (− 4.3% d⁻¹), and low CF (0.28), indicating very high stress levels of stocks induced by acute heavy rainstorms, leading to steeply fluctuated water temperatures. Subsequently, recuperation of stocks after the storm (D30 onwards) was significant during RCVR (Growth: 19% d⁻¹; Mortality: − 0.34% d⁻¹; CF: 0.41). Remarkably, the surviving shrimp (now > 0.5 g) became adapted and resilient, showing stable growth and survival despite another abrupt rainstorm with fluctuating water conditions at D45–46. On the other hand, Run 2 with a lower initial stocking density (56 m⁻²) showed better performance during ACCL (D1–10) and STBL (D11–30) with respective low mortality rates (− .2% d⁻¹ and − 0.75% d⁻¹) and high growth rates (24.4% d⁻¹ and 14.6% d⁻¹). However, two subsequent storms caused prolonged (> 10 d) rainfall during STRM, leaving only 4% survival at D38 with no RCVR phase. We showed that acute (~ 2 d) intense rainstorms can be detrimental to young (< 0.2 g) PL, but the stable environmental conditions after storms can allow the surviving stocks to recuperate, grow fast (> 0.5 g), then become quite resilient even to a subsequent acute (2 d) rainfall. However, extended rainstorms (> 10 d) cause continuous decline in salinity and temperature, leading to high mortality of shrimp. Therefore, careful programming of future on-site intermediate culture activities is important, considering the space and duration required for culture, initial densities and target sizes of PL, and cautious account of rainstorm seasonality.

Sea cucumbers are ecologically and economically important marine invertebrates, whose wild populations have been threatened by overfishing in recent decades. The rapid decline in wild stocks was driven by high market prices of sea cucumber products for food and medicine. Fortunately, recent developments in hatchery seed production technologies have paved the way towards establishing a more sustainable sea cucumber industry through aquaculture without dependence on massive collections from natural populations.

The sustainable mass production of rotifers is crucial to sufficiently supply marine fish hatcheries. However, maintaining a stable rotifer culture is still a challenge mainly due to unionized ammonia (NH₃) toxicity and biological contaminants. This study investigated the effectiveness of single initial inoculation of bioflocs (BF) in addressing the abovementioned problems on rotifer mass culture using Brachionus plicatilis subjected to three treatments for 29 days, namely: 1) water exchange (WE), 2) zero water exchange (ZE), and 3) bioflocs × zero water exchange (BF × ZE). The effects of feeding BF-cultured B. plicatilis and supplementing BF in the rearing water on the survival and growth of red sea bream Pagrus major larvae for 14 days were evaluated. Bacterial composition of BF was determined. BF inoculation resulted in significantly higher rotifer densities from day 14 to day 29 (BF × ZE with 226–434 individuals/mL vs WE and ZE with 69–131 individuals/mL). BF inoculation significantly controlled ciliate contamination (BF × ZE with 7–25 ciliates/mL vs ZE with 421–531 ciliates/mL) from day 21 to day 25. TAN and NH₃ concentrations were significantly reduced in the BF × ZE than in ZE and WE treatments on day 29. P. major larvae fed BF-cultured rotifers and reared in BF-supplemented water did not show reduced survival and growth. BF inoculation significantly improves B. plicatilis productivity through the effective removal of NH₃ via the ammonia-oxidizing activity of Nitrosomonas nitrosa and bacteria within the phylum Chloroflexota under prolonged zero-water exchange conditions. Furthermore, the study demonstrates the viability of BF in P. major larviculture.

The mangrove or mud crab (Scylla spp.) is among the most commercially important aquaculture species owing to its high demand in both local and international markets. However, the rapid expansion of farming activities has resulted in the intensive collection of wild stocks, posing a significant threat to natural populations. To address this, the Southeast Asian Fisheries Development Center Aquaculture Department (SEAFDEC/AQD) has developed basic larval rearing and nursery protocols for the farming of mangrove crabs. Despite these advancements, the hatchery production of seedstock remains insufficient to meet the growing demand for farming. One major challenge is the inconsistent larval quality in hatcheries, which is largely attributed to inconsistent broodstock performance. While numerous studies have explored both internal and external factors influencing the reproductive performance of mangrove crab broodstock in captivity, the findings remain fragmented. This review compiles existing research on mangrove crab maturation, providing a comprehensive overview of advancements in broodstock conditioning. It aims to identify research gaps and encourage further studies to develop improved protocols for managing captive broodstock effectively.

This study compared gonad development between wild-sourced and hatchery-bred silver therapon Leiopotherapon plumbeus. Wild fish from the east bay area of Laguna de Bay, Philippines, and hatchery-bred stocks grown to adult size in outdoor tanks were sampled, and somatic condition, gonad histology, gonadosomatic index (GSI), gut index (GI), and hepatosomatic index (HSI) were assessed during the annual reproductive cycle. Hatchery-bred fish condition was generally better than that of wild-sourced fish as a consequence of readily available food resources and environmental conditions. Hatchery-bred male GSIs were significantly higher than in wild male fish in November to February, coinciding with low water temperatures. However, female GSIs were significantly higher in July and November to December for the hatchery-bred fish, and in January to April for the wild-sourced fish. Together with spermatozoa and primary growth oocytes which were most abundant in the gonads, the presence of other gametogenic stages supports asynchronous gonad development. Hatchery-reared fish showed significantly higher GIs during the spawning season over their wild counterparts. Generally, mean HSI, regardless of sex, was also higher among hatchery-bred fish. These results suggest marked differences in the somatic and reproductive potential of wild and hatchery-bred silver therapon, although the presence of spermatozoa and vitellogenic oocytes in the gonads may allow this species to reproduce year-round.

The invention relates to the protocol for harvesting of microalgae, Chaetoceros calcitrans by manipulation of electrolytic flocculator settings. The harvesting system comprised of a holding tank for the microalgae, a DC power supply with variable voltage selector, ammeter and voltmeter. The best settings of 6/6 units Al/Pb probes with voltage selector set at point 1 to supply 3 volts to complete the electrolytic cell. The Pb in the paste was reduced by 97% with values of 34.27 ± 0.39 ppm with 0 - 0.24 ppm Pb in the effluent discharge. The Pb content in secondary live food, Artemia salina was further reduced by 78% based on feeding trials with 7.8 ± 5.1 ppm Pb content. This system will be beneficial to hatcheries for use onsite due to its simplicity and affordability.