Late maturation and large size at maturity are significant challenges when administering hormonal treatments in captive broodstock. Here, we report the potential of yeast, Pichia pastoris, as a vehicle to orally deliver a recombinant gonadotropin-releasing hormone (rGnRH1) aimed at stimulating gonadal development in juvenile orange-spotted grouper, Epinephelus coioides. Two recombinant GnRH1 constructs were designed utilizing pPIC3.5, the yeast expression vector lacking a signal sequence, hence retaining the recombinant within the yeast. The first construct (rGnRH1_1xGAP) comprised of GnRH1 decapeptide and the GnRH-associated peptide (GAP) separated by a cleavage site. The second construct (rGnRH1_10x) consisted of ten GnRH1 decapeptides, each separated by a cleavage site. Expression of the two recombinant peptides was confirmed by mass spectrometry. ELISA for the GnRH analogue (GnRHa) was validated to determine the level of rGnRH1 from the yeast extracts. Parallelism between the serially diluted GnRHa and serially diluted extracts from recombinant yeast confirmed validity of the assay. A luciferase reporter assay showed stimulation of tilapia GnRH type 3 receptor by the yeast extract, suggesting biological activity in vitro. In a short term experiment, lyophilised yeast loaded in gelatine capsules and fed once to juvenile orange-spotted grouper resulted in a significantly higher plasma GnRH compared with the control. In a 4-week experiment, lyophilized yeast containing either rGnRH1_1xGAP or rGnRH1_10x was incorporated in fish pellets and fed daily at a dose of 1 μg rGnRH1/kg fish body weight/day. The mean gonadosomatic index and oocyte diameter did not vary between the treated and control fish. The mean plasma levels of FSH, LH and GnRH in the rGnRH1-fed and control fish did not also vary significantly, however there were individuals in the rGnRH1-fed groups that had increased level of the hormones. Together with histological evidence showing oocyte development in a proportion of fish fed with the recombinant, results of the present study point to a biological activity in vivo of the rGnRH1 in yeast. With further refinement, this technology has the potential to provide a non-invasive method for broodstock management of large, late-maturing species of fish and of small, delicate endangered species that require breeding in captivity.

This is the first report on hydrodynamic models to determine current and water residence time patterns for Matarinao and Murcielagos bays in the Philippines, which have a long history of harmful algal blooms (HABs). Field surveys were conducted in Matarinao Bay in April and August 2010 and in Murcielagos Bay in February 2011. Hydrodynamic models of the bays were developed, and spatially explicit water residence times were estimated from the models based on rates of concentration decrease of a tracer within the bay. Both bays exhibited two distinct areas – the mouth with faster current flow and low residence time, and the head area with slower current flow and higher residence time. During the southwest monsoon, the residence time at Matarinao Bay was 5 d longer than that during the northeast monsoon. Phytoplankton sampling in both bays confirmed blooms of Pyrodinium bahamense, but the spatial distribution did not consistently correlate with the simulated residence time patterns. While residence time plays a significant role in algal blooms, extraneous factors may also influence the distribution of phytoplankton within embayments.

Monosex culture was proven to be an effective rearing method for grow-out, but in a closed-cycle hatchery, males and females are usually reared communally in tanks until maturation. This study determined the effect of communal rearing (CR) and separate rearing (SR) on male and female Penaeus indicus broodstock gonad maturation. This study also evaluated the influence of the rearing method on reproductive behavior and mating success. The results showed that CR female broodstock had higher maturation rates at 77.78 ± 5.31% (p = 0.061) and a shorter latency period at 6.71 ± 2.54% than SR females (p = 0.211), but the differences were not statistically significant. Similarly, maturation rates for both male groups were 40.62 ± 3.12% and were not significantly different (p = 1.00). The interspermatophore period (p = 0.044), spermatophore weight (p = 0.878), count (p = 0.780), viability (p = 0.257), and percent abnormality (p = 0.257) did not vary between males. In terms of the effect of rearing method on reproductive behavior, males from the SR group initiated more chase (p = 0.018) and fight with other males (p = 0.022) than CR males did, and the differences were significant. SR males also touched the discarded molt (p = 0.167) and advanced to the probe position (p = 0.525) more times than CR males, but the differences were not significant. The sum of all the reproductive behaviors was also significantly higher in the SR (54.00 ± 1.20) than in the CR (24.20 ± 0.86) groups (p = 0.017). Initial results showed that successful mating in the SR (80%) was higher than that recorded in the CR group (20%). These findings suggest that monosex rearing of male and female P. indicus will not negatively affect gonad maturation and will enable sex-specific nutritional manipulations, which can even possibly promote higher mating success.

Evaluation of appropriate hormone and ideal broodstock age for optimal breeding efficiency may ensure the production of good quality eggs and larvae in the hatchery. In this study, the spawning response of captive silver therapon Leiopotherapon plumbeus to various hormonal treatments and broodstock age was examined. In Experiment 1, spawning success, latency period, absolute and relative fecundity, fertilization and hatching rates, and larval production of female silver therapon broodstock were determined after ovulation and spawning in response to human chorionic gonadotropin (hCG; 5000 and 10,000 IU/kg), Ovaprim (0.5 ml/kg), hCG + Ovaprim (5000 IU + 0.5 ml/kg; 10,000 IU + 0.5 ml/kg) or hCG + domperidone (5000 IU + 0.5 ml/kg; 10,000 IU + 0.5 ml/kg). In Experiment 2, reproductive performance of four domesticated broodstock age groups (1⁺, 2⁺, 3⁺ and 4⁺-year old) was examined for five consecutive months, coinciding with the spawning season. Higher dose of hCG + Ovaprim resulted in higher spawning (100%), fertilization (99.7 ± 0.1%), and hatching (85.8 ± 5.5%) rates than the other treatments. The effect of age on reproductive indices was not significant. However, better spawning performance was observed in 1⁺ to 3⁺-year old broodstock, with higher fertilization (96.8–98.5%) and hatching (63.7%–77.2%) rates than among the oldest age group (82.9% and 57.2%). Together, results suggest that the combination of hCG + Ovaprim is highly effective in inducing ovulation and spawning in silver therapon, and that domesticated broodstock up to 4⁺ years of age could still be used for breeding activities and seed production.

Studies on the biology and ecology of sea lice are lacking in tropical regions such as in Southeast Asia where finfish cage farming has grown dramatically in the past decades. This study investigated the seasonal population dynamics of ectoparasites infecting captive snubnose pompano (Trachinotus blochii) breeders in marine cages in the Philippines. The pompano breeders were found to be naturally coinfected with caligid copepod Lepeophtheirus spinifer and capsalid monogenean Neobenedenia sp. These breeders were monitored and examined bimonthly (n = 10 per sampling) from September 2017 to May 2018, covering the warm season and cold season in the Philippines. Our results clearly show that L. spinifer population maintain a 100 % prevalence throughout warm and cold seasons however, mean abundance and intensity increased only during the cold months (early November to early March) and displayed an oscillating trend during this period. Highest mean intensity was recorded in early January (221.4 ± 24.6; temperature = 27.5 ± 0.3 °C; salinity = 34.8 ± 0.3 ppt) while the lowest mean intensity was recorded during the warm months dipping to 12.5 ± 1.9 in early May (temperature = 30.5 ± 0.3 °C; salinity = 30.3 ± 0.3 ppt). The prevalence of adult and pre-adult was high throughout the monitoring period at 70–100 % except at the start of summer (late March to early May) for pre-adult (30–90 %). In comparison, the chalimus stages were only observed during the cold months specifically from early November to late January with prevalence of 40–80 %. The highest mean abundance (3.4 ± 0.7) and mean intensity (4.3 ± 0.6) was in early November which coincided with the first peak of the total L. spinifer population. Neobenedenia sp. occurred year-round with no significant changes in the population mean abundance and mean intensity between warm and cold seasons. This study presents comprehensive information on the seasonal population dynamics of L. spinifer and Neobenedenia sp. in the Philippines, providing valuable insights on the ecology of caligid sea louse which is fundamental in the formulation of control and management strategies of these economically significant ectoparasites.

The tropical ornamental fish industry requires the stock to be reared in captivity before being sold; thus, exposing them to various handling- and transport-related stressors. A number of commercially available anesthetics are used during fish husbandry procedures, but these products are expensive and not readily available to small-scale ornamental fish operators. The use of sodium bicarbonate as an inexpensive anesthetic during routine husbandry activities in molly, Poecilia sp., a freshwater ornamental fish was assessed in terms of its effect on sedation, recovery and survival post-exposure in three independent experimental runs. Juvenile molly were exposed to sodium bicarbonate at a concentration of 100 g L⁻¹ and the time to sedation and recovery were monitored. It took longer for the fish to be fully sedated than their recovery. Survival of the fish a week post-exposure ranged 40-60%. Simulated transport of fish for 6 hrs in water containing 1 g L⁻¹ of sodium bicarbonate showed survival ranging 70-100% a week after transport. These findings demonstrated that sodium bicarbonate could be potentially used as a low-cost anesthetic during handling and short-term transport of ornamental fish. Future studies shall focus on discovering the underlying physiological mechanisms in fish following sedation with this chemical.

The growth efficiency, productivity and economic viability of Indian white shrimp (Penaeus indicus) fed with diet containing 40% (CP_high) and 34% (CP_low) crude protein (CP) levels were determined in a 90-day grow-out culture trial. Growth parameters including average body weight (ABW), specific growth rate (SGR), survival and feed conversion ratio (FCR) were not statistically different. CP_low had lower overall shrimp production (797.53 kg/ha, DOC 90), but was not significantly different from CP_high (843.78 kg/ha, DOC 90). The mean values for the water parameters of both treatments, such as DO, pH, salinity, temperature, TAN, NO₂-N, NO₃-N and PO₄-P, also showed no significant differences. However, the TAN values of CP_high were consistently higher from day of culture (DOC) 63 and increased significantly (p = .048) at DOC 90. Furthermore, the total bacterial and Vibrio counts in both treatments were not significant throughout the culture period. The economic analysis revealed that CP_low obtained higher net profits (6093 USD/ha/year), return on investment (72%) and discounted benefit–cost ratio (1.73). The current study found that feeding a low protein diet to P. indicus is economically viable and profitable and results in improved growth efficiency and productivity while also improving water quality and lowering nitrogen discharge.

Feeding 3.9 and 6.7 mg Hg/kg (Se/Hg molar ratios of 0.8 and 0.4, respectively) for 14 days negatively affected Dicentrarchus labrax growth and total DNTB- and thioredoxin-reductase (TrxR) activities and the transcription of four redox genes (txn1, gpx1, txnrd3, and txnrd2) in the liver, but a diet with 0.5 mg Hg/kg (Se/Hg molar ratio 6.6) slightly increased both reductase activities and the transcription of txn1, gpx1, and txnrd2. Feeding 6.7 mg Hg/kg for 53 days downregulated the genes of the thioredoxin system (txn1, txnrd3, and txnrd2) but upregulated gpx1, confirming the previously proposed complementarity among the antioxidant systems. Substitution of 20% of the feed by thawed white fish (hake) slightly counteracted the negative effects of Hg. The effects were not statistically significant and were dependent, in a non-linear manner, on the Se/Hg molar ratio of the feed but not on its Hg concentration. These results stress the need to consider the Se/Hg molar ratio of the feed/food when evaluating the toxicity of Hg.

Polychaete aquaculture has progressed in some countries to meet the high demand of fish bait and aquaculture industries. However, knowledge on the aquaculture requirements of polychaetes in the grow-out is still scarce. The present study aimed to determine the optimal feeding rate (FR) and sediment depth (SD) for the grow-out culture of mud polychaete Marphysa iloiloensis from early juvenile to adult stage. The effects of two FRs (50 and 100 g m⁻²) with three different levels of SD (2, 3, and 5 cm) on M. iloiloensis survival, growth performance, and biomass were evaluated. The study was performed in a 2 × 3 factorial experiment using completely randomized design with four replicates per treatment that lasted 120 days. Early juveniles (30 days old) were stocked in glass tanks at 1000 individuals m⁻² and grown for 120 days (herein refer as 'adult', with musculature and capable of reproduction). Regardless of FR, M. iloiloensis had the highest survival of 45 ± 2% in 5 cm SD but statistically comparable to 3 cm SD (34 ± 5%), while survival was significantly lowest in 7 cm SD (26 ± 3%). The levels of nitrite (NO₂) and total ammonia nitrogen (TAN) was significantly higher in the rearing water of 100 g m⁻² FR than in 50 g m⁻² FR. Higher FR resulted to poor water quality and appeared to contribute to the low M. iloiloensis survival in 100 g m⁻² FR. Growth performance was similar among treatments. There was a significant interaction between FR and SD on M. iloiloensis biomass (p < 0.05). In 50 g m⁻² FR, no difference was observed in the different levels of SD while in 100 g m⁻² FR, biomass was significantly higher in 5 cm SD than in 7 cm SD (p < 0.05). M. iloiloensis biomass in 50 g m⁻² FR was higher compared to 100 g m⁻² FR, regardless of the SD. Overall, the culture of M. iloiloensis using 50 g m⁻² FR in 3–5 cm SD showed the best survival and biomass. Based on these findings, it is recommended that the grow-out culture of M. iloiloensis from early juvenile to adult should follow the 50 g m⁻² FR and should be done in tanks with 3–5 cm SD to improve production.

This study examined the effects of co-feeding Artemia and commercial feeds on survival, growth and fatty acid composition of silver therapon Leiopotherapon plumbeus early juveniles. Triplicate groups of 36 days post hatch (DPH) early juveniles (17.09 ± 1.69 mm; 0.07 ± 0.02 g) were stocked in nine glass aquaria at 25 individuals per aquarium and reared for 60 days on three feeding regimes: (A) Artemia + powdered commercial tilapia feed (35% crude protein (CP)); (B) Artemia + powdered commercial prawn feed (38% CP); and (C) Artemia nauplii only as the control group. Early juveniles co-fed Artemia and commercial feeds had significantly higher survival (97%) than those fed Artemia alone (86%). Except for the condition factors that were similar to the control group, higher mean total length (30.2 ± 1.3 mm and 27.6 ± 1.2 mm), body weight (401 ± 64 mg and 339 ± 46 mg), length- (SGRL; 0.95 ± 0.07%/day and 0.80 ± 0.07%/day) and weight-specific growth rates (SGRW; 2.85 ± 0.27%/day and 2.58 ± 0.22%/day) were also observed in the co-feeding groups, independent of protein, fat and other nutrient levels in commercial feeds. Higher levels of long-chain polyunsaturated fatty acids were reflected in early juveniles co-fed Artemia and commercial feeds than those fed exclusively on Artemia contributing, in part, to the higher growth and survival observed in the co-feeding groups. Together, these results suggest that co-feeding strategy showed best results in terms of growth and survival, and that commercial feed with 35% protein and 6% crude fat levels may be beneficial in supplementing live feed with essential nutrients to optimize production of silver therapon fry during nursery culture.