Yield and agar quality of three red seaweed Gracilaria species grown in tanks at three salinities
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Gracilaria changii, G. firma and G. tenuistipitata were collected from the eastern coast of Sorsogon in southeastern Philippines and grown in concrete tanks at the SEAFDEC Aquaculture Department in Iloilo in May-June and in September-October 1994 at a stocking density of 1 kg/m2 and at three salinities (15, 25, and 35 ppt). In the first run, the highest specific growth rates per day were 2.5% at 25 ppt for G. changii, 3.6% at 35 ppt for G. firma, and 3.2% at 15 ppt for G. tenuistipitata. In the second run, the highest daily growth rates were 1.4% for G. changii, 1.2% for G. firma, and 3.3% for G. tenuistipitata, all at 15 ppt. Nutrient and light limitation in the second run led to lower and even negative growth rates. Gracilaria changii and G. firma were euryhaline but grew best at 25–35 ppt; G.tenuistipitata was not euryhaline and grew best at 15 ppt. The highest growth rates in tanks were at salinities close to those in the natural habitat: G. changii at 25 ppt, G. firma at 35 ppt, and G. tenuistipitata at 15 ppt. The estimated potential production (dry weight kg/m2-yr) in tanks was 1.65 kg G. changii at 25 ppt, 2.49 kg G. firma at 35 ppt, and 2.35 kg G. tenuistipitata at 15 ppt. Agar yields from three Gracilaria species varied from 5% to 23%, on average lowest in G. tenuistipitatata, and were generally higher at 25 ppt and 35 ppt than at 15 ppt. Agar gel strengths were also strongly affected by salinity and were highest at 35 ppt. Gracilaria tenuistipitata had very high gel strength (average 782 g/cm2 but as high as 1,082 g/cm2 comparable to agarose), well above the specified 750 g/cm2 for the international market. Gracilaria changii and G. firma had average gel strengths of 516 and 558 g/cm2, well within the range (400–600 g/cm2) for commercial agar used in the food industry. The sulfate contents were lower at 15 ppt and were even 0% in several instances, especially in G. tenuistipitata. The gelling temperature of 32°C and melting temperature of 97.3°C qualifies G. tenuistipitata for the international market. Gracilaria changii and G. firma had melting temperatures of 93–95°C but gelling temperatures of just 29°C. Farming techniques for these seaweeds should be developed to produce enough raw material for profitable commercial processing.
Ferrer, M. S. R., & Marasigan, A. N. (2007). Yield and agar quality of three red seaweed Gracilaria species grown in tanks at three salinities. In T. U. Bagarinao (Ed.), Research Output of the Fisheries Sector Program (Vol. 2. Reports on Fisheries and Aquaculture, pp. 129-137). Quezon City, Philippines: Bureau of Agricultural Research, Department of Agriculture.
PublisherBureau of Agricultural Research, Department of Agriculture
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Conference paperAQ Hurtado-Ponce - In Report on a Regional Study and Workshop on the Taxonomy, Ecology and Processing of Economically Important Red Seaweeds, 24-27 January 1995, Bangkok, Thailand, 1996 - Network of Aquaculture Centres in Asia-Pacific
Series: NACA Environment and Aquaculture Development Series No. 3Research in seaweed from 1988–1994 focused on the agar producing Gracilaria. Studies in the following areas were also conducted: inventory of the seaweed resources; production ecology; farming systems; and agar characterisation. Six species of Gracilaria and one Gracilariopsis abound in the Western Visayas. There were monthly variations in biomass and agar quality of G. blodgettii, G. manilaensis and G. heteroclada collected at different places. The bulk of the studies were carried out on Gracilariopsis heteroclada because of its wide distribution, fast growth characteristics and good quality agar. Its reproductive state was seasonal with tetrasporophyte abundant in May and carposporophyte in January. Seventy-five percent harvesting of the available biomass was sufficient for the next cropping season. Harvesting the seaweed using “araña” was not appropriate in places where the biomass was exposed to air during the lowest tide. The addition of nutrients to the stock increased the growth rate of the seaweed and gel strength of the agar. G. heteroclada grown at lower stocking density in hapa nets, both in floating cages and in ponds, gave higher growth rates and production than at higher stocking densities. This species, when polycultured with P. monodon at lower stocking density combinations, gave the highest growth rate and income. Likewise, this species when cultured vertically in ropes inside a floating cage showed encouraging results. G. heteroclada, when grown at 24–25 ppt under tank conditions, produced the highest gel strength.
Conference paperAQ Hurtado-Ponce - In TU Bagarinao & EEC Flores (Eds.), Towards sustainable aquaculture in Southeast Asia and Japan: Proceedings of the Seminar-Workshop on Aquaculture Development in Southeast Asia, Iloilo City, Philippines, 26-28 July, 1994, 1995 - Aquaculture Department, Southeast Asian Fisheries Development CenterResearch on seaweeds focused on the carrageenan-producing Kappaphycus alvarezii and the agar-producing Gracilaria spp. Growth of K. alvarezii was better on horizontal lines than on vertical or cluster lines from bamboo rafts. All morphotypes (brown green, and red) grew faster at 50 cm than at 100 cm below the water surface, but the green morphotype showed better carrageenan properties. A socioeconomic survey of K. alvarezii farming in Panagatan Cays, Antique revealed that a farmer has an average annual production of 3 tons/ha (dry) with the fixed bottom and hanging longline methods. Three species of Gracilaria in natural beds in lloilo showed monthly variations in biomass and agar quality; G. heteroclada had the highest biomass and gel strength. When this species was grown in tanks, growth and agar sulfate content were influenced by the interaction of light, salinity, and nutrients. Enriched and unenriched stocks of G. heteroclada differed in agar quality. When G. heteroclada was grown with the tiger shrimp Penaeus monodon in extensive ponds, the highest growth rate and production were obtained at the seaweed stocking density of 250 g/m2; this was in November when average water temperature, transparency, and salinity were low. Salinity tolerance varies among Gracilaria species.Oyster (Crassostrea iredalei) and mussel (Perna viridis) farming in Western Visayas were assessed in 1992 in terms of the culture methods, socioeconomics, marketing, and profitability. A more localized survey of oyster and mussel fanning was conducted through rapid rural appraisal in two coastal towns in 1993. A farmer-participatory study followed in 1994 for the culture of oysters, mussels, seaweeds, and rabbitfishes in a river mouth in Dumangas, lloilo. Green mussel, brown mussel (Modiolus metcalfei), and seaweeds transplanted to Dumangas from Capiz have reproduced. In another study, the green mussel was tested as a biological filter in tiger shrimp ponds; shrimps stocked with mussels grew better than those without. A nationwide survey on the Placuna placenta fishery in 1993 showed 27 remaining 'kapis' beds; many others have been depleted due to excessive gathering, pollution, siltation, and trawling. Broodstocks are being developed to produce 'kapis' seed for grow-out and restocking. For the first time at AQD, adult donkey-ear abalone Haliotis asinina from the wild spawned naturally in laboratory tanks. Juvenile abalones can be successfully grown on Gracilaria or abalone diet.
ArticleTR de Castro -
The Philippine Scientist, 1993 - San Carlos Publications, University of San CarlosAgar from three species of Gracilaria, G. changii G. coronopifolia, and Gracilariopsis heteroclada, collected form Panay and Guimaras islands was evaluated. Each species was pretreated with NaOH solution before extraction. Highest agar yields were obtained following alkaline pretreatment at the lowest concentration (1% NaOH) for all species. Highest gel strengths were obtained at different alkaline pretreatment conditions: 644 ± 3.4 g cm-2 at 3 % NaOH for 60 min for G. changii, 641 ± 11.9 g cm-2 at 5 % NaOH for 30 min for G. heteroclada, and 170 g cm-2 at 5 % NaOH for 30 min G. coronopifolia. Agar gelling temperatures ranged from 38.5-40ºC and agar melting temperature ranged from 80.5-85 ºC. Specific viscosity was highest for agar from G. changii at 18 cps. Moisture and ash contents ranged from 8.04-15.20 % and 4.32-4.98%, respectively. Based on the result for this study, G. heteroclada and G. changii are two species which merit further studies for their prospective commercial value to the different industries using agar.