Pond Trials Research Articles

Selective Control of Common Carp: Ineffectiveness of 2-(Digeranylamino)-ethanol (GD-174) in Pond Trials

The candidate piscicide, 2-(digeranylamino)-ethanol, (commonly known as GD-174) was subjected to efficacy trials in ponds under a wide variety of conditions. Results of the trials were disappointing considering that laboratory tests had shown the compound to be selectively toxic to common carp (Cyprinus carpio). Results of pretreatment, on-site toxicity tests were misleading and indicated concentrations that failed to kill all of the carp in 19 of 23 ponds. In a few instances, the chemical killed the carp with little or no effect on nontarget fishes. No fish were killed in some trials and large numbers of nontarget fishes were killed in others. Twenty of 25 pond trials were judged to be unsuccessful. Success or failure of pond treatments could not be correlated with any particular combination of physical, chemical, and biological factors. Because the activity of GD-174 against mixed populations of fish cannot be predicted, further development of this compound as a selective toxicant for carp has been discontinued at the National Fishery Research Laboratory.

Partial and complete replacement of fishmeal by soybean meal in feeds for intensive culture of carp

Feeding experiments with carp were performed in plastic tanks, in cages and in experimental ponds, using pelleted rations of 25% total crude protein. Fishmeal was the only source of supplemental protein in the control ration, besides the basal ground grains. Partial replacement (40% of the fishmeal) by soybean meal in pond trials required only supplements of methionine and 5% oil in order to attain the same growth, protein and energy utilisation as with the control ration. When most or all of the fishmeal was replaced by soybean meal, supplements of methionine, 0.4–0.5% lysine and 10% oil were necessary to achieve gains, protein efficiency ratio (PER), net protein utilization (NPU), protein retentions and energy retentions equal to those of the control fishmeal ration. It was concluded that regular soybean meal contains 10–15% less available energy and 10–15% less available lysine for carp than the generally accepted values (as in NRC-NAS, Nutrient Requirements of Poultry, 1977).

Experimental pond production of marron, Cherax tenuimanus (Smith) (Decapoda: Parastacidae)

Forty-two, 4-month pond trials were carried out on a large indigenous crayfish in south-western Australia — a candidate species for commercial aquaculture. Since growth rate and density are inversely related in this species the aim was to establish an intermediate range of density giving commercially acceptable values of growth rate and biomass. Survival over 4 months averaged 80.5% (30.7–100%) and was independent of density in the range 2–15/m 2; low values (two below 50%) were due to oxygen depletion from overfeeding. The complex relationship between mean individual weight gain/4-month trial and initial mean individual weight was described indirectly using Mauchline's (1977) linear plot of log growht rate in length against initial length. A multiple regression equation accounted for 93.3% of the variability in log growth rate with 45.7% due to initial size, 40.6% due to seasonal water temperatures, 6.1% due to initial density and 0.8% due to feeding rate. Similar transformations were used to relate statistically production and biomass change to initial mean weight. Growth, production and biomass schedules were constructed for the most favourable temperature area of the south-west. A mean weight of 45 g at a biomass of 2100 kg/ha was predicted for the end of the first year of life and 111 g at 3175 kg/ha for the second year. Wide variability in individual weights represents a marketing problem. Plant material (poultry and lucerne pellets, compost) was supplied at rates of up to 1.0 kg/m 2 per 4 months as a substrate for detrital formation. Pollution from these materials generated limiting oxygen deficiencies.

Supplemental feeds containing coffee pulp for rearing Tilapia in Central America

A supplementary feed containing 30% coffee pulp was evaluated for use in the culture of Tilapia aurea in El Salvador, Central America. A comparison of the coffee pulp feed with a feed containing all of the same ingredients except coffee pulp was made with T. aurea raised in 1.0-m 3 cages suspended in a fertilized earthen pond. Survival was high in all treatments and there was no significant difference in average weight gain between groups of fish receiving the two experimental feeds. Production trials were conducted in 100-m 2 fish pens and in 0.05-ha earthen ponds. Pen-raised fish receiving coffee pulp feed grew faster throughout the experiment, and total production was approximately twice that in control treatments. Highest production in pens was 1.25 kg/m 2 per year. Results of production pond trials using T. aurea at 9 000/ha and stocked with the piscivorous Cichlasoma managuense yielded an estimated 3 392 kg/ha per year in fed treatments and 2 049 kg/ha per year in controls. Low feed conversion (1.92) and low feed cost resulted in an increase in net annual earnings of $251.00/ha.