Identification of pen shells (Bivalvia: Ostreida: Pinnidae) collected off northern Iloilo, Philippines using their morphological characters

This study describes morphological characteristics of pen shells collected along the coast of northern Iloilo, Philippines. A total of 380 pen shell individuals with intact shells and their adductor muscles were carefully examined and measured. Eleven species were studied, namely: Atrina pectinata (Linnaeus, 1767), Atrina inflata (Dillwyn, 1817), Atrina vexillum (Born, 1778), Atrina seminuda (Lamarck, 1819), Atrina rigida ([Lightfoot], 1786), Pinna bicolor Gmelin, 1791, Pinna atropurpurea Sowerby, 1825, Pinna deltodes Menke, 1843, Pinna muricata Linnaeus, 1758, Pinna incurva Gmelin, 1791, and Pinna nobilis Linnaeus, 1758. The species were identified based on the nine characteristics of the valve for the genus Pinna and eight for the genus Atrina. These characteristics were then correlated with their adductor muscles’ morphology. Analysis of variance revealed that the three most dominant species investigated under genus Atrina, namely Atrina pectinata, Atrina inflata, and Atrina vexillum, were found to be significantly different in the eight characters of the valve (P < 0.05). Moreover, three representative Pinna species, Pinna bicolor, Pinna atropurpurea, and Pinna deltodes, were significantly (P < 0.05) different based on shell width, dorsal posterior shell margin, sulcus width, and dorsal posterior margin to dorsal nacreous margin. The observed high correlation (P < 0.05) between adductor muscle properties and different shell length characteristics for five dominant species can be used as a predictor of growth and suggests that the increase in the size of adductor muscle correlates to the increase in the size of the mentioned shell characteristics. No previous study of this kind was conducted in the Philippines. This work provides relevant information for related biological research on other pen shell species and for the management of pen shell resources in northern Iloilo and, possibly, other regions in the world

Effect of a Seasonal Fishery Closure on Sardine and Mackerel Catch in the Visayan Sea, Philippines

The implementation of seasonal fishery closures (SFC) can be controversial due to the frequent lack of clear objectives, monitoring and empirical evidence of management success. In the Philippines, an SFC implemented for the conservation of important fishery commodities in the Visayan Sea has been ruled a success after stricter implementation of this fishery policy in 2012. However, a comprehensive, detailed, and robust analysis of this fishery policy is lacking. Using a difference-in-differences (DID) framework, we estimated the effect of SFC on the interannual and seasonal catch for sardine and mackerel. We expanded our analysis to other species not regulated under the SFC policy. We also conducted semi-structured interviews (N = 235), focus group discussions (N = 9) and key informant interviews (N = 37) involving municipal fisheries stakeholders in the surrounding municipalities around the Visayan Sea, and representatives from the government and non-government agencies, to complement our analyses. Seasonal analyses of catch data show a significant increase in sardine catch at the end of the seasonal closure among SFC-participating provinces. However, overall, the SFC had no significant effect on sardine interannual catch among the provinces participating in the SFC. We also found no significant effect of the SFC on interannual and seasonal catch for mackerel. Furthermore, our findings show no significant changes in fishing pressure to other aquatic species. Interview results corroborate our DID findings for mackerel, but not for sardine. The varying perceptions on the outcomes of the SFC policy can be attributed to several challenges such as lack of implementing guidelines, lack of alternative livelihoods for the affected stakeholders, persistence of illegal fishing, and uneven implementation of the SFC. Since the management objective of this SFC was to conserve the regulated species, alternative management measures may be needed to achieve this goal. This could entail more consistent enforcement, improved cooperation and communication between fisheries managers and stakeholders, fish size or gear restrictions, and identification and conservation of key habitats needed to restore overexploited species

Physiological and avoidance responses of juvenile mud crab Scylla serrata to mercury

The physiological and avoidance responses of juvenile mud crab Scylla serrata to mercury was evaluated by determining mortality using a renewal-type acute toxicity test and assessing crabs’ ability to avoid toxic concentrations. The 96-h LC50 of mercury to juvenile mud crab was computed to be 0.04 mg L-1. When transferred to clean waters, crabs that survived exposure to concentrations lower than 0.04 mg L-1 had better chances of surviving than those that were exposed to higher mercury concentrations. Avoidance of juvenile mud crabs to mercury was determined using a fluvarium, which provided the crabs a choice between untreated and Hg-treated waters. Results showed that juvenile crabs were not able to avoid waters that contain 0.1 mg L-1 mercury, a concentration that was more than twice the 96-h LC50 value. Juveniles previously pre-exposed in 1/50th of the 96-h LC50 value had a higher avoidance threshold and were not able to avoid waters with 1 mg L-1 mercury. Results suggest that juvenile mud crab is unable to avoid waters containing lethal levels of mercury and this may have potential impacts on crab biomass, distribution, growth, and development

Value chain analysis of the horse mussel Modiolus metcalfei (Hanley, 1843) fishery in Iloilo, Philippines

The exploitation of horse mussels Modiolus metcalfei (Hanley, 1843) in Dumangas, Iloilo has been going on for decades, yet effective fisheries management remains hindered by the poor understanding of the fishery. A value chain analysis was conducted to provide a better understanding of the horse mussel fishery in the area and identify upgrading strategies. Mapping of the value chain used data gathered through fisherfolk interviews, key informant interviews, and field observations. The collectors, processors, retailers, and ambulant vendors are the key players in the fishery. It is a sphere of both men and women who create value additions along the chain. While both men and women may engage in marketing, the majority of men are involved in the collection while women do the processing. The collector-cum-ambulant vendor benefits the most with a monthly income of PHP10,892.78 (USD217.86) with value addition of PHP8.30 kg-1 (USD0.17), followed by the collector with a monthly income of PHP9,597.46 (USD191.95) with a value addition of PHP4.00 kg-1 (USD0.08) and retailer with a monthly income of PHP5,000.00 (USD100.00) with value addition of PHP4.55 kg-1 (USD0.09). The actor who benefits the least in this value chain is the processor with a monthly income of PHP4,185.10 (USD83.70) with value addition of PHP2.30 kg-1 (USD0.05). Upgrading strategies at every node of the value chain along with its enabling strategies were proposed to improve the income of key actors and maximise the economic benefits from the horse mussel fishery

Interactive influence of dietary protein and lipid on maturation of Indian white prawn, Penaeus indicus broodstock

The establishment of protein and lipid requirements for growth of penaeid species is essential in maximizing productivity but information on the effects of these nutrients on gonad maturation is still lacking. Indian white prawn, Penaeus indicus (H. Milne Edwards) broodstock, were fed formulated maturation diets containing varying levels of dietary protein (35, 45 and 55%) and lipid (6, 12 and 18%) combinations following a 3×3 factorial design. Control group was fed with fresh mussel, squid and polychaete. Results indicate that treatment groups receiving diets of 45/18 and 55/12 protein/lipid combinations and the control exhibited higher maturation rates than the other treatments (p = 1.9 × 10−4). Shrimp broodstocks fed diets containing the lowest protein or lipid levels exhibited poor gonad maturation. Hepatopancreas damage and gonadal atresia were apparent in treatments with high dietary lipid based on histological and biochemical analyses. The diet with 55/12 protein/lipid combination is therefore best recommended for P. indicus gonad maturation. This study demonstrated that a well‐formulated diet that satisfies the protein and lipid requirements can support successful gonadal maturation comparable with feeding the broodstocks fresh maturation diets.This study was funded by Department of Science and Technology-Accelerated Science and Technology Human Resource Development Program, Student Research Support Fund and SEAFDEC/AQD (FD-02-C0219T). The help of the staff from the Shrimp Hatchery and Nutrition and Feed Development Section and the assistance of Vince Louie Sumalinog and Elmer Ajerra during the conduct of this study are gratefully acknowledged. We thank the valuable advice of Mr. Vicente Balinas for the statistical analysis and Ms. Erish Estante-Superio (DP-01-C2017T) for providing the test animals

The influence of monosex rearing on gonad maturation and reproductive behavior of Indian white prawn, Penaeus indicus broodstock

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.This study was funded by the Department of Science and Technology-Accelerated Science and Technology Human Resource Development Program, Student Research Support Fund and SEAFDEC/AQD (FD-02-C0219T)