PART III
LABORATORY EXERCISES
AND
FIELD DEMONSTRATIONS

LABORATORY DEMONSTRATION NO. 1¹
Freshwater Quality Analysis

1. PROCEDURES

1. Water sample was collected from a pond and analyzed for dissolved oxygen concentration using the Winkler Method.

2. Water pH was measured with a Beckman pH meter.

3. Water temperature (15 cm below the surface) was recorded with a thermometer.

4. Transparency of the pond water was determined with a secchi disc.

2. OBSERVATIONS

The following measurements in the water analysis were made:

1. Dissolved oxygen concentration - 8.0 ppm (mg/1)

2. pH - 6.8

3. Temperature - 28°C

4. Secchi disc reading - 0.20 m

¹ Conducted by Ms. Victoria Adora at the Freshwater Fisheries Research Station, Los Baos, Laguna, Philippines.

LABORATORY DEMONSTRATION NO. 2¹
Biological Examination of Pond Water

1. PROCEDURES

1. Water samples were taken from the concrete pools of the station and examined for the presence of phytoplankton and zooplankton.

2. A stereomicroscope was used to see the different plankters. The organisms were then fixed in 10% formalin and identified under the high power objective of a compound microscope.

2. OBSERVATIONS

1. The deep green color of the water indicated the presence of bluegreen algae which were identified as Microcystis, Anabaena and Oscillatoria. Diatoms such as Navicula, Coscinodiscus and Melosira were found in the water samples. Phacus and Euglena were some of the dinoflagellates identified.

2. Among the zooplankters identified were rotifers of the genera Keratella and Brachionus. Cladocerans such as Bosmina, Moina and Ceriodaphnia were also observed.

¹ Conducted by Ms. Luzviminda Guerrero at the Freshwater Fisheries Research Station, Los Baos, Laguna, Philippines.

LABORATORY EXERCISE NO. 1¹
Species Selection: Milkfish and Nile Tilapia

1. PROCECURES

1. Harvestable size milkfish (Chanos chanos) and Nile tilapia (Tilapia nilotica) were obtained from the market and dissected.

2. The mouth parts and gill rankers of the fishes were examined and compared.

3. The digestive tracts of the specimens were removed from the abdominal cavities for examination and comparison.

2. OBSERVATIONS

1. The milkfish had a small and toothless mouth. Its gill rakers were fine and numerous. The digestive tract of the species had a long intestine with pyloric appendages.

2. The tilapia had a mouth with fine teeth and gill rakers which were fewer and coarser than those of the milkfish. It had a long, coiled intestine.

3. Both fishes were found to be herbivorous in feeding habit.

¹ Conducted by Ms. Luzviminda Guerrero at the Lakeview Hotel, Los Baos, Laguna, Philippines.

PRACTICAL EXERCISE NO. 2¹
Marine Cage and Raft Construction

1. PROCEDURES

1. The design and construction of a floating cage for marine fish were explained by the instructor.

2. The participants took part in the making of the cage net using knotless nylon netting.

3. Rigging of the net cage to the raft was tried by the participants with the guidance of skilled workers.

2. OBSERVATIONS

1. The participants were able to observe close-hand the materials and methods used for the construction of a floating cage for marine fish culture.

2. The participants gained first-hand experience in the making of a net cage and in rigging the net to the floating raft.

¹ Conducted by Mr. Chan Wong, Kat O Marine Station, Hong Kong.

FIELD DEMONSTRATION NO. 3¹
Making and Repair of Fishpen Nets

1. PROCEDURES

1. The making and repair of fishpen net enclosures using polyethylene netting and nylon twine were demonstrated by skilled workers. The various knots utilized were shown to the participants.

2. The instructor explained the methods in the making and repair of fishpen nets. He also described the materials being used by the workers.

2. OBSERVATIONS

1. The participants observed the methods of fishpen construction and repair being practised by local farmers.

2. It was learned by the participants that the fishpen nets usually last for about 2–3 years. Regular checking and repair is, however, necessary to prevent the loss of fish due to damage of the nets by natural causes or poachers.

¹ Conducted by Engr. Vicente Alferez in Mayondon, Los Baos, Laguna, Philippines.

LABORATORY EXERCISE NO. 3¹
Marine Water Quality Analysis

1. PROCEDURES

1. Water samples were collected from two marine sites, the Kat O Marine Station and Aberdeen Station, in the morning.

2. Water temperature at two depths, near the surface and two meters below the surface, was recorded.

3. Water samples were analyzed in the laboratory for pH, salinity, dissolved oxygen concentration and ammonia concentration.

2. OBSERVATIONS

1. The water samples collected from the Kat O Marine Station had lower ammonia and higher dissolved oxygen than those in the samples from Aberdeen. These results indicated that the marine water in the Aberdeen area was more polluted than that in Kat O.

2. Water temperature was generally higher at the lower depth than near the surface. This was attributed to the cold wind blowing over the water surface.

3. The water salinity and pH in the two areas were similar.

¹ Conducted by Mr. Tai Kwan Mok at the Aberdeen Research Station, Hong Kong.