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Seasonal variations can affect the concentration of trace elements, and the change in their concentrations can affect the natural productivity of freshwater aquaculture ponds. Hence, we studied the seasonal variations of the 12 pre‐selected trace elements (Co, Cu, Fe, Mn, Zn, Se, Ca, Mg, P, S, Al, Si) and their relationships with primary and secondary productivity in two aged ponds, stocked with three different life stages of marron (Cherax cainii), for a period of 1 year. Trace element analysis was performed by using (Agilent, ICP‐OES). Except Co and Se, all trace elements, and primary and secondary productivity were influenced by seasonal variation. The pond age significantly influenced the concentrations of some trace elements. On a seasonal basis, trace elements were positively correlated with the plankton abundance, species diversity, and wet and dry plankton weights. Seasonal variations and pond age affected the dissolved concentrations of trace elements and plankton productivity.

The present feeding trial examined the effect of synbiotic use of Bacillus mycoides and organic selenium (OS) as Sel-Plex on marron immunity, growth and survival. The marron were cultured in recirculated tanks and fed test diets consisting of a basal diet; basal diet supplemented with B. mycoides (108 CFU g−1 of feed); basal diet supplemented with OS (Sel-Plex) (0.2 g kg−1 of feed) and basal diet supplemented with synbiotic (B. mycoides at 108 CFU g−1 and OS 0.2 g kg−1 feed) diet, in triplicate. The effect of the prebiotic OS (Sel-Plex) on the growth rate of B. mycoides was also studied in vitro. The results suggested that synbiotic use of B. mycoides and OS significantly improved some immune parameters of marron, particularly the glutathione peroxidase, and to some extent total haemocyte counts. However, the synbiotic feed did not synergistically improve marron growth, in fact the use of B. mycoides-supplemented diet alone demonstrated significantly higher growth in marron compared with the growth of marron fed on other test diets. Supplementation of the basal diet with host origin B. mycoides significantly increased the intestinal bacterial population (3.399 ± 825 CFU g−1 of gut) in marron compared with other diets. Organic selenium as Sel-Plex in Trypticase Soya Broth also confirmed that OS did not increase the amount of growth of B. mycoides and resulted in a lower intestinal bacterial population in the synbiotic diet-fed marron. In conclusion, synbiotic of OS and B. mycoides may improve a particular immune parameters of marron and to a lesser extent their growth.

A 90-day feeding trial was conducted to determine the effects of dietary organic selenium (OS) supplementation on immune responses, total selenium accumulation in various tissues and the digestive system health of marron Cherax cainii. A group of marron (initial weight 3.65 � 0.05 g) were fed 0.2 g kg � 1 of Sel-Plex as a source of OS and were compared to a control group of marron that were not fed OS. After 90 days of feeding OS, total haemocyte counts (THC) and the percentages of granular and semigranular cells in marron were significantly higher than in marron fed a control diet. However, dietary OS did not affect the proportion of hyaline cells. The marron fed OS had significantly lower bacteraemia and longer neutral red retention times than the control group. Total selenium levels in the haemolymph, hepatopancreas and muscle tissues of the OS-fed marron group were significantly higher (P < 0.05) than in control diet group. The highest total soluble selenium levels were found in the muscle tissues of OS-fed marron on the final day of the feeding trial. Amylase and protease activity, soluble protein, and numbers of microvilli were significantly higher (P < 0.05) in marron fed OS. These findings demonstrate the benefits of including 0.2 g kg � 1 OS in marron diet to enhance immune parameters, increase total selenium accumulation in muscle and improve marron digestive system health.

The current study evaluated the effect of soluble dietary cellulose on growth, survival and digestive enzyme activity in three endemic, Australian freshwater crayfish species (redclaw: Cherax quadricarinatus, marron: C. tenuimanus, yabby: C. destructor). Separate individual feeding trials were conducted for late-stage juveniles from each species in an automated recirculating freshwater, culture system. Animals were fed either a test diet (TD) that contained 20% soluble cellulose or a reference diet (RD) substituted with the same amount of corn starch, over a 12 week period. Redclaw fed with RD showed significantly higher (p

This study tested two premises. First, that there is a range in water temperature within which to artificially incubate marron eggs and hatchlings, which enables a combination of rapid development, high survival, and the production of large juveniles. Second, that the population density of marron eggs and hatchlings incubated artificially can be increased without altering development time, survival, or juvenile body weight. Marron eggs were collected from 31 gravid females and artificially incubated at four water temperatures (i.e. 16°C, 20°C, 24°C, 28°C), while eggs were collected from eight females and artificially incubated at three population densities (i.e. 0.35, 0.70, 2.80 eggs mL−1). The eggs and hatchlings were assessed for development time and survival as they hatched and developed into juveniles. The juveniles were weighed at the conclusion of the incubation period. As water temperature was increased from 16°C to 28°C, there was an inverse curvilinear relationship between development time and water temperature, the time required for the eggs to hatch and develop into juveniles decreasing from 70.2 to 24.5 days. However, at 16°C and 28°C, the survival of the eggs and hatchlings was reduced (i.e. 83.8% and 87.7% at 20°C and 24°C vs. 70.4% and 57.5% at 16°C and 28°C), while incubation at 28°C resulted in the development of small juveniles (i.e. 29.7, 29.2, and 28.5 mg at 16°C, 20°C, and 24°C vs. 25.1 mg at 28°C). In comparison with water temperature, increasing the population density of the eggs and hatchlings from 0.35 to 2.80 eggs mL−1 did not have a significant effect on development time, survival, or juvenile body weight. The two premises tested in this study were supported, demonstrating that marron eggs and hatchlings can be artificially incubated at high population densities, and are most successfully incubated in water maintained between 20°C and 24°C.

Marron and yabbies are farmed commercially in Western Australia and are native and introduced species respectively. Genetic improvement of farmed stock for aquaculture can be achieved by choosing particular strains, by selective breeding or by producing hybrids of different strains. Studies into the taxonomy and growth of both marron and yabbies have shown variation between geographically isolated populations. This variation may offer potential for selecting strains that demonstrate desirable traits for aquaculture, such as improved growth rates. In addition to selection of wild strains that demonstrate desirable traits for aquaculture, further advances in production may be achieved by selection of characteristics in captive stock that are heritable. In marron, moderate proportions of the phenotypic variation in growth rate, tail and chelae size have been shown to be heritable (h2 = 0.3–0.6). Recent research into yabby genetics involved assessing growth and reproductive characteristics of geographically isolated populations of yabbies inhabiting a range of ecotypes throughout Australia. Growth rates and size at sexual maturity varied among populations. However, there was no significant difference in the sex ratio between these geographically isolated groups. The main focus of the yabby genetics research has been to develop a method to prevent or reduce reproduction of yabbies. Uncontrolled reproduction in this species results in high densities and smaller animals because growth is density dependent. Preventing reproduction and thereby controlling densities in yabby ponds or dams can be achieved by stocking monosex populations. The stocking of monosex populations results in an estimated 70% increase in gross income. Hybidization of yabby populations was investigated as a method of controlling reproduction. Sterile hybrids were produced by crossing yabbies from geographically isolated populations. These experiments have also revealed a hybrid cross that consistently produces only male progeny. If this all-male hybrid strain performs as well as all-male monosex pond stock, achieved by manual sexing, the production of large, and therefore higher value, yabbies will be increased in the commercial aquaculture industry.

Stocking and harvest data from 45 grow-outs of the crayfish Cherax tenuimanus (Smith 1912) on a commercial farm were analysed to give predictive equations for survival, mean weight and individual weights of crayfish at harvest. Density dependence was a major factor influencing variation in survival and mean weight. Harvest mean weight decreased, and biomass increased, with density. The crayfish price ($ kg−1) employed to estimate the market value of harvested crayfish increased with individual weight from a minimum saleable weight of 40 g. For grow-out of 0+ year-olds for 1 year, the market value was a maximum at low stocking densities of 1.5-2.0 m−2. Further grow-out for 1 year of the unsaleable weight range (20-40 g) of 1+ year-olds, gave a harvest value which increased with stocking density. Comparison of predicted and actual cohort numbers and mean weights for a further 1 5 harvests showed no bias in prediction and a mean precision level of 16% for numbers and 11% for mean weight.