Induced breeding and seed production of bighead carp Aristichthys nobilis (Richardson)

A 40-page manual that details the advanced induced spawning technology for Bighead carp developed at SEAFDEC/AQD through the years. This handbook emphasizes the adoption of efficient carp hatchery techniques for optimal production of good quality eggs and juveniles

Resistance to a heavy metal mixture in Oreochromis niloticus progenies from parents chronically exposed to the same metals

Poster presented at the Fifth International Symposium on Genetics in Aquaculture, June 19–25, 1994, Halifax, Nova Scotia, Canada.Adult Oreochromis niloticus were mass spawned in concrete tanks. The one-month old progenies (F1) were exposed for two months to a mixture of 0.01 mg L−1 Hg, 0.1 mg L−1 Cd and 1.0 mg L−1 Zn. The survivors were grown to sexual maturity in a natural environment (lake). The fish were spawned and the progenies (F2) of the exposed F1 (EF1) were exposed to another mixture of the three metals: 3.0 mg L−1 Zn, 0.30 mg L−1 Cd and 0.01 mg L−1 Hg, both in a static and static-renewal system. Another group of F2 from unexposed F1 (UF1) received the same treatment. Results showed that in both exposure systems, survival of the F2 of EF1 was significantly higher (P<0.05) than those from UF1. The medial lethal time (LT50) of the F2's were estimated from the time-response curve following regression analysis: 5.16 days (F2 of UF1) and 9.03 days (F2 of EF1) in the static exposure experiment; 3.34 days (F2 of UF1) and 5.52 days (F2 of EF1) in the static-renewal run. Exposure of the parental stock resulted in the culling out of individuals which were more susceptible to the heavy metals. The more resistant members of the population (survivors) which have the ability to adapt to the toxicants were able to pass on the resistance to their offspring. The results are supported by other studies in the field which demonstrate high resistance in populations of organisms living in contaminated sites

Effects of long-term exposure to a mixture of cadmium, zinc, and inorganic mercury on two strains of tilapia Oreochromis niloticus (L.)

Tilapia are an economically important group of fish. They have a short generation period of 3-6 months, and exhibit successive breeding. In addition, their fast growth, herbivorous or omnivorous feeding habits, high food conversion efficiency, ease of spawning, ease of handling, resistance to disease and good consumer acceptance make this group of fish highly popular in aquaculture in Asia, Africa and other developing countries. Tilapia have been the subject of research on pollution effects over the last decade. The purpose of this study was to determine growth, accumulation and depuration responses of 2 strains of the Nile tilapia, Oreochromis niloticus, chronically exposed to a mixture of heavy metals including cadmium, zinc and mercury

Cage culture of the giant freshwater prawn (Macrobrachium rosenbergii)

An extension manual describing biology, site requirement, grow-out operations, health management, harvest, post harvest handling and processing, and economic analysis

Cage culture of the Pacific white shrimp Litopenaeus vannamei (Boone, 1931) at different stocking densities in a shallow eutrophic lake

Postlarvae of Litopenaeus vannamei were acclimated and stocked in lake-based cages at the following stocking densities: 10, 20, 30 and 40 shrimp m−2. Another set of shrimp was stocked in concrete tanks as reference samples at 30 shrimp m−2. Significant differences were observed among stocking densities throughout the 95-day culture. The final weight at harvest decreased with increasing stocking density: mean weights of 23.3, 15.8, 13.0, 10.9 and 14.6 g for the 10, 20, 30, 40 shrimp m−2 and reference tanks were observed respectively. There were no significant differences in survival throughout the culture period, ranging between 69% and 77%. Daily growth rates (range: 0.11–0.24 g day−1) and specific growth rates (range: 3.54–4.34%) also differed significantly among stocking densities, both increasing with decreasing stocking density. The feed conversion ratio in the cages did not differ among the stocking densities, ranging from 1.53 to 1.65. The relationship between stocking density and mean individual weight at harvest followed the equation $y=81.06x^{-0.54} (R^{2}=0.938)$ and that of stocking density and production (in g m−2) is $y=58.01x^{−0.46} (R^{2}=0.834)$

Effects of low nitrogen-phosphorus ratios in the phytoplankton community in Laguna de Bay, a shallow eutrophic lake in the Philippines

The effects of low nitrogen-phosphorus ratios on microalgae from a large eutrophic freshwater lake in the Philippines were investigated. Natural microalgal populations from Laguna de Bay, the largest lake in the Philippines, were cultured using three different nitrogen-phosphorus weight ratios (2N:1P; 6N:1P and 12N:1P) at two phosphorus concentrations (0.25 and 0.5 mg l–1) in each case. The growth and genera composition of the cultures under the different treatments were followed for a 12-week period. Community level responses were assessed based on species richness (s), Shannon-Wiener Index (H’), Simpson Index (λ) and Evenness (J’). Among the different microalgal groups, only the chlorophytes showed a significantly higher density in response to the 12N:1P treatment at the higher P concentration, indicating that the nutrient ratio had a significant interaction with the nutrient levels used in the experiments. The genera found in the different treatments were generally similar; however, the degree of dominance of some varied with treatment during the experiment. The succession of dominant genera also differed among the N:P treatments. The diatoms like Fragilaria, Aulacoseira (= Melosira) and Nitzschia dominated the lowest N:P. On the other hand, chlorophytes (Kirchneriella and Scenedesmus) dominated the highest N:P treatment, particularly from the second to the seventh week of the experiments with the diatoms becoming co-dominant only towards the eighth week until the end of the experimental. The 6N:1P treatment showed a mixed dominance between the diatoms and the chlorophyte genera. The various indices of diversity indicate significantly lower diversity only in the 12N:1P at 0.5 mg l–1 P and not in 12N:1P at 0.25 mg l–1 P.This study was part the doctoral dissertation of the senior author at Hohenheim University, Germany. Funds for the study was provided in part by the European Union STDIII Program as component of the project ‘Laguna de Bay, Philippines: An Ecosystem Approach for Sustainable Management’ under contract CT 94-0334. Additional funds were provided by SEAFDEC/AQD under project code FS-03-F97B. The Deutschen Akademischen Austauschdienstes DAAD supported the senior author’s stay in Germany. Mr F. Reyes assisted in the culture and field collection of the samples. Dr. SF Baldia assisted in the identification of the samples

Culture of Macrobrachium rosenbergii (De Man 1879) in experimental cages in a freshwater eutrophic lake at different stocking densities

Macrobrachium rosenbergii (de Man 1879) juveniles (0.4 g) were cultured in experimental cages (L × W × H: 2.5 × 1 × 1 m) in Laguna de Bay, the largest lake in the Philippines. The following stocking densities at four replicates each were used: 15, 30, 60 and 90 prawns m−2 of cage bottom. The mean sizes at harvest after 5 months of culture ranged from 14.3 g for the highest stocking density to 26.3 g for the lowest. The mean size at harvest, daily growth rate and size class distribution were significantly influenced by stocking density, with those at the lowest stocking density showing significantly better growth and overall proportion of larger prawns. Heterogeneous individual growth (HIG) was fairly evident in all treatments. The percentage of blue-clawed males was not influenced by treatment but the mean weight was significantly higher in the lower stocking densities. Both the percentage and mean weight of berried females were significantly higher in the lowest stocking density. Survival was the highest in the lower stocking densities (55.3%, 54.0%, 52.7% and 36.9% for 15, 30, 60 and 90 prawns m−2 respectively). Feed conversion ratio (FCR) improved with decreasing stocking density, ranging from 2.1 to 3. As expected, yield per cropping increased with stocking density and ranged from 450 to 1089 g m−2 yr−1 of actual cage area. Production values obtained in the cage cultured M. rosenbergii were comparable to or even higher than those reported from pond culture, given that the stocking densities used in this study were generally higher than in ponds. The results show that the farming of M. rosenbergii in cages in lakes is a viable alternative to pond culture and has the potential of improve aquaculture production in lakeshore fish farming communities.The authors thank Mr. Federico Reyes for his assistance in the conduct of this experiment. Funding was provided by SEAFDEC/AQD under study code: FS-05-C2003B

Microcystins in natural blooms and laboratory cultured Microcystis aeruginosa from Laguna de Bay, Philippines.

Laguna de Bay, the largest freshwater lake in the Philippines, experiences periodic blooms of the cyanobacteria Microcystis aeruginosa. Blooms of these cyanobacteria in 1996, 1998 and 1999 were sampled. HPLC and MALDI-TOF mass spectrometry were used to analyze for microcystins. A total of 16 structural variants of the toxin were isolated from the samples with microcystin LR (MC-LR) as the most abundant variant in the samples from 1996 and 1999 making up 77 to 85% of the total, respectively. MC-RR was the dominant variant in the 1998 bloom making up 38%. The samples from 1996 had the highest total toxin concentration (4049 µg g-1) followed by those from 1998 (1577 µg g-1) and 1999 (649 µg g-1). A strain of M. aeruginosa previously isolated from the lake was also cultured in the laboratory under different nitrogen concentrations (1, 3 and 6 mg L-1) and elevated phosphorus concentration (0.5 mg L-1) to determine the influence of these factors on toxin production. A total of 9 different structural variants of microcystin were isolated from the laboratory cultures with MC-LR consisting more than 75% of the total in all treatments. No significant differences in the total toxin concentration as well as the % distribution of the different variants among treatments were observed. However, the strain of M. aeruginosa cultured in the laboratory had from 3 to 20 times higher total microcystin than those harvested from the lake.This study was part of the EU-funded project "Laguna de Bay, Philippines: An Ecosystem Approach for Sustainable Management" under contract CT 94-0334. Additional funds were provided by SEAFDEC/AQD under Project FS-03-F97B. The senior author was supported by a grant from the Deutscher Akademischer Austauschdienst (DAAD). Dr. S. F. Baldia provided the M. aeruginosa isolates and Mr. E Reyes assisted in the culture and field collection of the samples

Breeding and seed production of the giant freshwater prawn (Macrobrachium rosenbergii)

An extension manual describing biology, broodstock management, hatchery and nursery operations, feeding management, packing and transport, and health management of the giant freshwater prawn

Practical water chemistry for fishfarmers I. Teaching strategies

Years of ambitious, yet seemingly futile, efforts by the authors in the Philippines in making fishfarmers comprehend and appreciate chemical reactions the way chemists do, paved the way for the formulation of teaching strategies that communicate water chemistry. Theoretical concepts, being well understood, served as a springboard for farmers in translating abstract ideas into field situations. Laboratory practicals become less intimidating as standard laboratory glasswares and material were replaced by day to day material within the farmer s easy reach