Richard W. Soderberg

Effects of Rearing Density on Growth, Survival, and Fin Condition of Atlantic Salmon

Abstract Parr of Atlantic salmon (Salmo salar) were reared to final densities of 0.53-4.29 lb/ft2 of rearing container bottom area under conditions of constant temperature, water quality, and diet. Growth and survival were not affected by density. After 171 d, the condition of pectoral and dorsal fins had not changed from that initially recorded and did not differ among treatments. We conclude that rearing density alone does not affect growth, survival, or fin condition of Atlantic salmon reared at densities likely to occur at production hatcheries.

Influence of tank design and hydraulic loading on the behavior, growth, and metabolism of rainbow trout (Oncorhynchus mykiss)

Subadult rainbow trout (Oncorhynchus mykiss) stocked at 48 kg/m3 (3 lb/ft3) were subjected to treatments of tank design (rectangular plug flow, circular, and cylindrical cross flow) and water exchange rate (1·5 and 2·5 exchanges/h) to determine their effects on fish behavior, growth, and metabolism. Ambient light levels and current velocities were also measured in each of three tank sectors (upstream, middle, and downstream) to determine their relative contributions to behavioral effects. Tank design significantly affected fish orientation to current, contact time with tank surfaces, and frequency of agonistic encounters, though aggression levels were relatively low overall. Gradients in fish distribution by sector were greatest in plug-flow tanks. Effects were either modified or eliminated by increasing the water exchange rate from 1·5 to 2·5/h. Multiple-regression analysis showed the following hieararchy of independent-variable effects on fish distribution: tank type > exchange rate > aggression level > current velocity > light level. Significant effects of tank design were also observed on fish growth in terms of biomass gain (cross flow > plug flow > circular). These results were matched in metabolic studies, where both oxygen consumption and ammonia excretion were highest in circular and lowest in cross-flow tanks. Reduction (cross-flow compared with circular tanks) in oxygen consumption averaged 13·6%, ammonia excretion 17·5%. These results were also modified by an increase in water exchange rate. Tank-design effects on fish metabolism and growth may be mediated, at least partly, through changes in fish behavior.

Effects of Rearing Density on Growth and Survival of Lake Trout

Abstract Lake trout (Salvelinus namaycush) were reared at density indices (allowable density in pounds/cubic foot divided by fish length in inches) of 0.25, 0.50, 1.0, and 2.0 in cages suspended in circular tanks. Water flow rates were such that dissolved oxygen remained above 8 ppm within all the cages. Thus treatment effects were attributed to density and not influenced by water quality. Growth and condition were not affected by density, but survival was lower at the higher density than at the three lower densities. We conclude that lake trout may be successfully reared at a density index of at least 1.0 if the water requirements for respiration and waste dilution are met.

Growth, Survival, and Food Conversion of Atlantic Salmon Reared at Four Different Densities with Common Water Quality

Abstract Our objective was to determine the maximum effective rearing density for Atlantic salmon (Salmo salar) at 17.5°C, a temperature typically used in hatcheries to accelerate growth. We reared 5.8-g (mean weight) parr for 80 d to final rearing densities of 14–55 kg/m2 (rearing unit bottom area) or 80–310 kg/m3 (rearing unit volume). Weight gain was slightly depressed in fish at a final rearing density of 26 kg/m2 (146 kg/m3), but mortality, food conversion, and gain in length were not affected. At densities greater than 26 kg/m2, fish growth was slower and food conversion was higher, but mortality was unaffected. Atlantic salmon may be reared at 17.5°C to densities of at least 14 kg/m2 (80 kg/m3) without adverse effects on growth and health, but final rearing densities should not exceed 26 kg/m2.

The Effects of Ionic Strength on Un-ionized Ammonia Concentration

Abstract Ionic strength affects the ionization of ammonia and the resulting un-ionized ammonia (NH3) concentration. The error introduced by failure to account for this effect can be substantial in marine or brackish water. We present a simple method for correcting the calculation of the NH3 fraction in an ammonia solution for ionic strength.

Growth and Survival of Walleyes Reared in Ponds Fertilized with Organic or Inorganic Materials

Abstract Fry of walleye Stizostedion vitreum were reared for 40 d at a density of 16 fish/m3 in ponds fertilized with organic or inorganic matter and at 50 fish/ m3 with inorganic fertilization. Al the lower density, inorganic fertilization was more economical than organic fertilization, and fish survival was unaffected by fertilizer treatment. Although fish lengths were similar in both treatments, fish in the inorganically fertilized ponds gained less weight than those in the organically fertilized treatment. At the higher density, fish survival was unaffected, but growth was reduced so that the fish were unacceptably small for stocking. Fish production did not vary significantly among the treatments, but was lower at the higher density than reported in similar studies. Production may have been limited by low alkalinities in the ponds. Ponds receiving inorganic fertilizers had higher dissolved-oxygen levels than those fertilized with organic matter.

Lack of Response of Juvenile Walleyes to Increased Levels of Fertilization or Liming in Soft-Water Ponds

Abstract The growth, survival, and production of juvenile walleyes Stizostedion vitreum were not affected by increasing the rates of inorganic fertilization in earthen ponds by two and four times the originally proposed levels of 600 μg nitrogen/L and 30 μg phosphorus/L at each application. Fish growth and survival were both reduced in ponds stocked earliest in the season, regardless of the fertilization rate. This indicates that unpredictable spring weather is a more important factor than fertilizer nutrient levels in the pond production of walleye. We tested the hypothesis that fish production was carbon limited in these low alkalinity ponds by adding lime to some ponds as an experimental treatment. Ponds were stocked later in the spring to reduce variability due to weather. Total alkalinities increased in the limed ponds, but there was no effect on walleye growth, survival, or production. Additional large doses of limestone to all ponds further increased pond alkalinities but again failed to affect fis...

Temperature Effects on the Growth of Blue Tilapia in Intensive Aquaculture

Abstract Blue tilapias (Oreochromis aureus) were grown at 20, 25, and 30°C in closed aquaculture systems to develop a growth model for flowing-water husbandry of this species. Blue tilapias required 0.69 ± 0.05 temperature units (TU) per millimeter of growth in length (mean ± 95% confidence level; 1 TU = 1°C above 17.8°C maintained for 30 d). This requirement was verified in a second experiment in which blue tilapias were grown at 28°C on feed rations calculated from anticipated growth. The daily length increment (▵L, mm) of blue tilapias grown at constant temperature (T, °C) within the range 20–30°C can be predicted from the equation ▵L = 0.048T – 0.853.

Aeration of Water Supplies for Fish Culture in Flowing Water

Abstract An analytical approach to the reaeration of flowing water for aquaculture is presented, together with a rational method for the assignment of dissolved oxygen minima on the basis of respiratory characteristics of fish. Methods for calculation of expected oxygen transfer capabilities of gravity devices and mechanical units are given.

Linear Fish Growth Models for Intensive Aquaculture

Abstract Fish growth is frequently projected in time based on the temperature units required per increment of fish length. Temperature units are degree-days or degree-months and are derived by plotting growth on the horizontal axis and temperature on the vertical axis. Coldwater fish have a temperature intercept near 0°C, but the plot of warmwater fish growth is likely to cross the vertical axis at a considerably warmer temperature. This theoretical zero-growth temperature should be subtracted from the average water temperature to obtain an accurate growth model. Temperature units have been described for the Fahrenheit and Celsius scales for incremental growth in English and metric units of measure with and without the intercept correction. Different definitions of temperature units and scales of measurement and the complicated and confusing calculations required to predict fish growth in this manner necessitate a simpler universal method. A simple and useful fish growth model is obtained by regressing th...