The sulfide tolerance of milkfish and tilapia in relation to fish kills in farms and natural waters in the Philippines
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Fish kills of milkfish Chanos chanos and tilapia Oreochromis spp. now occur frequently in brackish, marine, and freshwater farms (ponds, pens, and cages) in the Philippines. Aquafarms with high organic load, limited water exchange and circulation, no aeration, and high stocking and feeding rates can become oxygen-depleted and allow sulfide from the sediments to appear in the water column and poison free-swimming fish. The sulfide tolerance of 2-5 g milkfish and 5-8 g O. mossambicus was determined in 25-liter aquaria with flow-through sea water (100 ml min-1) at 26-30 °C and sulfide stock solutions pumped in at 1ml min-1. Total sulfide concentrations in the aquaria were measured by the methylene blue method and used in the regression against the probits of % survival. Four experiments showed that the two species have similar sulfide tolerance. In sea water of pH 8-8.5, about 163 ± 68 μM or 5.2 ± 2.2 mg l-1 total sulfide (mean ± 2 se) or 10 μM or 313 μg l-1 H2S was lethal to 50% of the fish in 4-8 h, and 61 ± 3 μM total sulfide or 4 μM H2S in 24-96 h (to convert all sulfide concentrations: 1 μM = 32 μg l-1). Earthen pond bottoms had 0-382 μM total dissolved sulfide (mean ± sd - 54 ± 79 μM, n - 76); a tenth of the samples had >200 μM. The water column may have such sulfide levels under hypoxic or anoxic conditions. To simulate some of the conditions during fish kills, 5-12 g milkfish were exposed to an abrupt increase in sulfide, alone or in combination with progressive respiratory hypoxia and decreasing pH. The tests were done in the same flow-through set-up but with sulfide pumped in at 25 ml min-1. The lethal concentration for 50% of the fish was 197 μM total sulfide or 12 μM H2S at 2 h, but 28-53 μM sulfide allowed fish to survive 6-10 h. Milkfish in aquaria with no aeration nor flow-through sea water died of respiratory hypoxia in 5-8 h when oxygen dropped from 6 to 1 mg l-1. Under respiratory hypoxia with 30-115 μM sulfide, the fish died in 2.5-4 h. Tests with low pH were done by pumping a weak sulfuric acid solution at 25 ml min-1 into aquaria with flow-through sea water such that the pH dropped from 8 to 4 in 5 h. Under these conditions, milkfish died in 7-9 h when the pH was 3.5. When 30-93 μM sulfide was pumped in with the acid, the fish died in 2-6 h when the pH was still 4.5-6.3. Thus, sulfide, hypoxia, and low pH are each toxic to milkfish at particular levels and aggravate each other's toxicity. Aquafarms must be well oxygenated to prevent sulfide toxicity and fish kills.
CitationBagarinao, T., & Lantin-Olaguer, I. (1998). The sulfide tolerance of milkfish and tilapia in relation to fish kills in farms and natural waters in the Philippines.
PublisherKluwer Academic Publisher
Sulphides; Pollution tolerance; Fish kill; Sulphur; Fish physiology; Pond culture; Water quality; Pollution surveys; Agricultural runoff; Fish culture; Sulfides; Fisheries; Fish poisoning; Oxygen depletion; Toxicity testing; Aquaculture; Sediments; Chanos chanos; Oreochromis; Oreochromis mossambicus; Philippines; Hypoxia tolerance; Acid tolerance; Intensive farming
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Growth response of Nile tilapia fry to salinity stress in the presence of an ‘internal reference’ fish Growth of three strains of Oreochromis niloticus L. fry exposed to salinity stress in the presence of an internal reference fish were compared. The Central Luzon State University (CLSU) strain was obtained from the Freshwater Aquaculture Center, CLSU, Philippines. The ISRAEL strain was acquired from the Philippine government's Bureau of Fisheries and Aquatic Resources National Freshwater Fisheries Technology Center (BFAR-NFFTC), Munoz, Nueva Ecija. The National Inland Fisheries Institute (NIFI) strain was obtained from the NIFI, Bangkok, Thailand. Eight to nine full-sib families (replicates) per strain were split into two groups. One group was grown in freshwater for 2 weeks, acclimated to 32 ppt and reared for 2 weeks and finally grown in freshwater for another 2 weeks. Another group was contemporaneously grown in freshwater polyethylene tanks for 6 weeks. Each replicate family included a size-matched internal reference population of red tilapia strain. Two-way analysis of variance (anova) revealed no significant strain differences (P=0.081; r2=0.106). However, analysis of covariance with the internal reference strain used as a covariate showed significant (P=0.049; r2=0.638) strain effects on specific growth (based on standard length measurements). The ISRAEL strain showed consistently better growth rate in both saline and freshwater environments than the NIFI and CLSU strains. We estimated the statistical power of the two-way anova (ϕ=√(k′−1)(factor MS−s2)/(k′s>2); Zar 1984) to be ∼0.30. There was a 70% probability of a Type II error and no true difference in the growth of the three strains was detected. The use of internal reference strain as a covariate improved the r2 from 0.106 to 0.638 and increased the efficiency of the test in detecting a true difference. Other strain comparison studies in our laboratory at the Southeast Asian Fisheries Development Center Aquaculture Department showed that the ISRAEL strain shows better growth than the NIFI and CLSU strains in a crowding stress tolerance experiment, when fed only with rice bran and under restrictive feeding regimes.
Resistance of two Nile tilapia, Oreochromis niloticus (L.) strains exposed to a mixture of zinc, cadmium and inorganic mercury MLA Cuvin-Aralar - In CL Marte, GF Quinitio & AC Emata (Eds.), Proceedings of the Seminar-Workshop on Breeding and Seed Production of Cultured Finfishes in the Philippines, Tigbauan, Iloilo, Philippines, 4-5 May 1993, 1996 - Aquaculture Department, Southeast Asian Fisheries Development CenterTwo strains of one month-old Oreochromis niloticus namely CLSU (obtained from Central Luzon State University, Philippines) and NIFI (from National Inland Fisheries Institute, Thailand) were exposed to a sublethal mixture of 1.0 mg L-1 Zn, 0.1 mg L-1 Cd, and 0.01 mg L-1 Hg for two months in aquaria. Another set served as control with only BFS tapwater in the aquaria. At the end of the exposure period the fish were grown for another 2 months in net cages in Laguna de Bay. During the exposure (aquarium) and grow-out (lake) phases, the uptake and elimination of the metals were determined by AAS. Accumulation of the metals peaked at 13.9 µg g-1 Hg, 78.5 µg g-1 Cd, and 1447.0 µg g-1 Zn for NIFI and 14.2 µg g-1 Hg, 82.4 µg g-1 Cd, and 1591.3 µg g-1 Zn for CLSU lost 94.9% Hg, 98.76% Cd, and 89.99% Zn after two months in the lake. After the grow-out period, 2 females and 1 male of each strain were stocked in replicate polyethylene tanks. Time to first spawning, spawning frequency, fry production, and fry survival (after 30 days) were monitored. Results showed no significant effect of treatment and strain with respect to time to first spawning, spawning frequency, and mean fry survival. There was also no significant difference between the treatment and strain in mean fry production when dam weight was used as a covariate in the analysis. The results suggest that both strains of O. niloticus are resistant to long-term exposure to the metals. In addition, the elimination of the metals during the grow-out phase may have also diminished their effect on the breeders of the two strains.
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