Maximum Daily Growth Rate Research Articles

Production of the Australian freshwater silver perch, Bidyanus bidyanus (Mitchell), at two densities in earthen ponds

Silver perch fingerlings (mean weight 15.3 g) were stocked at densities of 21 000 and 7000 fish/ha in six 0.1-ha earthen ponds and cultured for 10 months. There were three replicate ponds for each density. Ponds were aerated for at least 11 h a day and water was added every 4 weeks to replace that lost by evaporation and seepage. Fish were fed a formulated diet containing 35% crude protein at 4% body weight per day for the first 4 weeks and at rates up to 3% thereafter. The mean annual production rate of 9819 kg/ha of fish stocked at 21 000/ha was significantly higher ( P < 0.01) than the annual rate of 3699 kg/ha of fish stocked at 7000/ha. The maximum daily production and growth rates achieved in any pond over a 1-month period during summer were 97.7 kg/ha and 5.1 g/fish, respectively. Stocking density did not significantly ( P > 0.05) affect survival rate (treatment means for 21 000 and 7000 fish/ha: 92.8 and 94.7%), daily growth rate (0.2–3.3 and 0.3–3.4 g/fish), weight at harvest (434.9 and 473.2 g), food conversion ratio (1.9:1 and 1.8:1) and cost of feeding ($A1.55 and $A1.47/kg), suggesting that higher stocking densities and production rates are possible. Water temperatures ranged from 11.1 to 30.0 °C. Significantly ( P < 0.05) slower growth during December was associated with concentrations of NH 3-N up to 0.65 mg/l. The results demonstrate that silver perch is an excellent species for semi-intensive culture in static earthen ponds with the potential to form the basis of a large industry in Australia, based on high-volume, relatively low-cost production.

The growth rate and growth efficiency of Streptocephalus macrourus (Crustacea, Anostraca) cultured on microalgae

Affordable biological technology for the reclamation of wastes and water of the waste streams from intensive livestock units is important in a country short of water. This study tested the concept of reclamation of waste by Streptocephalus macrourus (Crustacea: Anostraca) from the effluent of a high rate algal pond processing livestock wastes. S. macrourus showed a growth efficiency of 39% to 74% when fed optimal rations and cultured at densities between 10 and 400 1−1. The maximum daily growth rates (0.15–0.21) approximate the growth rates of cladoceran or rotifer cultures managed for maximal biomass production. S. macrourus' ability to withstand crowding enabled the production from S. macrourus cultures (up to 91.8 mg dry mass l−1 d−1, or 1241 mg wet mass l−1 d−1) to exceed production recorded from cladoceran or rotifer cultures. Temperature influenced growth rate, with the highest growth rate occurring at 24 °C. The dilution rate of continuously fed cultures influenced growth rate, with the optimum dilution rate tested being 10 ml organism −1 d−1. Mass mortality occurred when organisms were held at a density of 4000 l−1. S. macrourus is able to convert algae grown on livestock waste efficiently into anostracan biomass, and is able to give a very high daily production.

Moulting interval and growth of juvenile Antarctic krill (Euphausia superba) fed different concentrations of the diatom Phaeodactylum tricornutum in the laboratory

Juvenile Antarctic krill (Euphausia superba) were fed the diatom Phaeodactylum tricornutum at concentrations ranging from 0.0–5.0 mgCl-1. Intermoult period (IP) decreased, but an increment of body length per moult (ΔBL) of juvenile krill increased, up to a concentration of 1.0 mgCl-1. No further effect of food concentrations on IP or ΔBL was seen at concentration beyond 1.0 mgCl-1. IP plateaued at 23.8 days and ΔBL, 1.14 mm. The maximum daily growth rate (ΔBL/IP) of juvenile krill was calculated to be 0.047 mm day-1. ΔBL and IP were correlated and the relationship is expressed as ΔBL=-0.0066IP+2.47 (r=0.58, n=141, P<0.01). Growth conditions of krill in the Southern Ocean are discussed in terms of available food concentration in there.