In Australia, the widespread clearing of native vegetation has resulted in large areas of once-productive agricultural land being affected by rising saline groundwaters. There is considerable interest among farmers and rural landowners throughout Western Australia, in the possibilities that inland saline aquaculture may offer for a potentially productive use of land and water resources that can no longer support traditional agriculture. Black bream (Acanthopagrus butcheri) appear to be an ideal candidate for the developing saline aquaculture industry of inland Western Australia, however their current maximum growth rates are too slow for profitable production. The high productivity of modern breeds of terrestrial livestock species is primarily due to genetic improvement programs utilising selective breeding, and similar gains have also been made where they have been implemented for aquatic species. Before the growth rate of black bream can be genetically improved, however, it is necessary to estimate both the extent of genetic improvement required and the extent of genetic (co)variation in those growth traits which will be subject to, or affected by, selection. The aims of this study were to: (1) Determine the extent of genetic improvement in growth rate required for black bream to be considered as a profitable aquaculture species. (2) Estimate the potential for growth rate to be improved through heterosis when different black bream strains are crossbred. (3) Estimate the additive genetic variation for growth rate, which exists within populations of black bream. (4) Estimate the genetic (co)variation which exists between growth rate and other production traits. A partial budget analysis investigated whether enhanced growth rates of black bream would improve profitability and justify a genetic improvement program. It was conducted for two different fish production systems; a commercial operation that incurred more operating expenses due to costs associated with farm initiation (stand-alone farm model) and an existing farm that diversified into aquaculture using the saline water resources of established farm dams (integrated farm model). Sensitivity analyses indicated that a 33% increase in growth rate to at least 200g/annum would allow either production system to return a profit at a farm-gate price of AUS$6/kg whole fish, with fish survival rates of 98% for the stand-alone farm and 65% for the integrated farm model. These results provided a breeding objective, being an improvement in growth rate by at least 33%. A complete diallel cross of two black bream populations was used to estimate the comparative advantages that might be gained from straight-breeding and crossbreeding. At 90 days of age, the growth traits of standard length, total length and wet weight, varied significantly among all straight-bred and crossbred lines, and among half-sib groups within lines. Differences among half-sib groups explained 6.8% of the total variance in standard length, 8.3% in total length and 7.1% in wet weight, giving estimated heritabilities over all lines of 0.27 ± 0.11 for standard length, 0.33 ± 0.13 for total length and 0.28 ± 0.12 for wet weight. There was no evidence for heterosis in any traits when straight-bred and crossbred lines were compared, and phenotypic (rP = 0.95 – 0.98) and genetic (rG = 0.63 – 0.69) correlations were high among all growth traits. I used the estimated heritability for wet weight of 0.28 to optimise a factorial mating design from a single population, and to estimate the contribution of additive genetic, nonadditive genetic and maternal effects to variation in growth traits of black bream at 75, 130 and 180 days of age in the hatchery. Maternal genetic and environmental effects were greatest at 75 days of age, accounting for 9.1% of total phenotypic variance in wet weight, 11.4% of variance in standard length and 8.8% of variance in total length. At later ages maternal effects were much reduced, explaining 0.8 – 3.7% of phenotypic variance in growth traits. Additive genetic effects were greatest at 130 days of age, when they accounted for 17.4% of total phenotypic variance in wet weight, 21.4% of variance in standard length and 18.7% of variance in total length. Additive genetic effects were negligible (<1%) at 75 days of age and 4.8 – 5.5% of total phenotypic variance in growth traits at 180 days of age. Non-additive genetic effects (which also included common environmental effects due to families being raised in the same tank) explained 5.8 – 7.3% of total phenotypic variance in growth traits at 75 days of age, but were much smaller at later ages. Variable stocking densities among tanks up to 75 days significantly affected all growth trait measurements below 180 days of age. One of the most important of these traits is feed conversion efficiency. Feed conversion efficiency (FCE) is the effectiveness with which feed is converted to saleable fish product. Feed costs are a major input to aquaculture production systems and genetic changes in FCE may therefore have an important influence on profitability. FCE is usually expressed by a composite measure that combines feed intake and growth rate. The two most common measures are feed conversion ratio (feed intake/weight gain over a specified time interval) and its inverse, feed efficiency. Feed conversion ratio and feed efficiency are measures of gross FCE, because they do not distinguish between the separate energy requirements of growth and maintenance. There is abundant evidence of substantial genetic variation in FCE and its component traits in terrestrial livestock species and, although data are few, the same is likely for cultured fish species. The major problems with selecting from this variation to genetically improve FCE in fish species are: • It appears impractical to measure feed intake on individual fish, so that family mean data must be used. • We do not know the optimal time period over which to test fish for FCE. • We do not know the genetic correlations between FCE under apparent satiation or restricted intake conditions, or between FCE at different times in the production cycle. I measured the relationships between feed intake to apparent satiety and weight gain in replicate half-sib families of black bream at four times over a 56-day test period. After 42 days, I found significant additive genetic variance in both weight gain and feed intake, and a stabilisation in family group variation in both traits. This indicates that 42 days is the minimum test period over which to measure genetic variation for FCE in black bream. There were high, positive phenotypic (and probably genetic) correlations between weight gain and feed intake after 42 days. There was no detectable genetic variation for either feed efficiency (weight gain/feed intake), or residual feed intake, which is the difference between the actual feed intake of an individual and the intake predicted from its body weight and growth rate. I argue that selection for improved FCE might be better achieved not by using a composite measure, but by using a weighted selection index that accounts for the genetic covariance among weight gain, feed intake and other correlated traits.

Secondary salinisation has rendered over 100 million hectares of land throughout the world, and over 5 million hectares in Australia, unsuitable for conventional agriculture. The utilization of salinised land and its associated water resources for mariculture is an adaptive approach to this environmental problem with many potential economic, social and environmental benefits. Despite this, inland mariculture is yet to develop into an industrial-scale, rural enterprise. The main aim of this study was therefore to identify and address some of the technical and biological limitations to the development of an inland finfish mariculture industry. Three technical aspects essential to the development of an Australian inland mariculture industry were reviewed; potential sources of water, the species suitable for culture in these water sources and the production systems available to produce them. Based on factors such as their quantity, quality and proximity to infrastructure, the most appropriate water sources were deemed to be groundwater obtained from interception schemes and waters from operational or disused mines. In terms of species, mulloway (Argyrosomus japonicus) were identified as having many positive attributes for inland mariculture, including being temperate and therefore having the ability to be cultured year-round in the regions where the majority of secondary salinity occurs. Seasonal production of barramundi (Lates calcarifer) in ponds in the temperate climatic zones has potential, but may be more appropriate for those salinised water sources located in the warmer parts of the country. Rainbow trout (Oncorhynchus mykiss) were also identified as having excellent potential provided water temperature can be maintained below the upper lethal limit and also have potential for seasonal production, perhaps in rotation with barramundi. In terms of production systems, pond-based culture methods were found to have many advantages specific to inland mariculture. Static ponds enable culture in areas with low groundwater yield and more cost-effective potassium supplementation compared with flow through ponds. Static ponds also largely overcome the issues associated with the disposal of salt-laden and eutrophied waste water; however yields from static ponds are typically low and limited by the nutrient input into the pond. In response to the yield constraints of static pond culture, a new culture technology known as the Semi-Intensive Floating Tank System (SIFTS) was designed, patented and constructed in collaboration with the aquaculture industry and tested in a static inland saline pond in the wheatbelt of Western Australia. This technology was designed to reduce nutrient input into ponds by the collection of settleable wastes and to provide large volumes of well-oxygenated water to the target species, to ameliorate the loss of fish from low dissolved oxygen during strong microalgal blooms. The three species identified above has having excellent potential for inland mariculture (mulloway, rainbow trout, and barramundi) were grown in SIFTS held within a 0.13 ha static, inland saline water body (salinity 14 ppt) over a period of 292 days, yielding the equivalent of 26 tonnes/ha/year (total for all three species). Rainbow trout were grown with an FCR of 0.97 from 83 to 697 grams over 111 days (SGR, 1.91%/day) between June and September, when average daily water temperatures ranged from 12.3„aC to 18.2„aC. Over the same time period, mulloway grew only from 100 to 116 grams, however, once temperatures increased to approximately 21„aC in October, feed intake increased and mulloway grew to an average size of 384 grams over 174 days with an SGR and FCR of 0.68 %/day and 1.39, respectively. Barramundi stocked in November with an average weight of 40 grams increased to 435 grams in 138 days (SGR 1.73%/day) with an FCR of 0.90. The SIFTS significantly reduced nutrient input into the pond by removing settleable wastes as a thick sludge with a dry matter content of 5 to 10%. The total quantity of dry waste removed over the 292 day culture period was 527 kg (5 tonnes/ha/yr), which was calculated to contain 15 kg of nitrogen (144 kg/ha/yr) and 16 kg of phosphorus (153 kg/ha/yr). The release of soluble nutrients into the pond resulted in blooms of macro- and micro- algae which caused large and potentially lethal diurnal fluctuations in dissolved oxygen within the pond, however, comparatively stable levels of dissolved oxygen were maintained within each SIFT through the use of air lift pumps. It is well documented that saline groundwater is deficient in potassium which, depending on the extent of the deficiency, can negatively impact on the performance of marine species, including fish. The physiological effects of this deficiency on fish, however, have not been previously described. As such, I conducted a bioassay investigating the physiological effects of a hypersaline (45 ppt) groundwater source containing 25% of the potassium found in equivalent salinity seawater (i.e. 25% K-equivalence) on juvenile barramundi. Histopathological examination of moribund fish revealed severe degeneration and necrosis of skeletal muscles, marked hyperplasia of branchial chloride cells and renal tubular necrosis. Clinical chemistry findings included hypernatraemia and hyperchloridaemia of the blood plasma and lowered muscle potassium levels. It was concluded from this study that the principal cause of death of these barramundi was skeletal myopathy induced by unsustainable buffering of blood plasma potassium levels from the muscle. Although such hypokalaemic muscle myopathies have been previously described in mammals and birds, this was the first description of such myopathies in fish. It was hypothesized from the results described above that the physiological effects of potassium deficiency are dependent on salinity and that they would be ameliorated by potassium supplementation. These predictions were tested in a subsequent study which measured the effects of potassium supplementation between 25% and 100% K-equivalence on the growth, survival and physiological response of juvenile barramundi at hyperosmotic (45 ppt), near-isosmotic (15 ppt) and hyposmotic (5 ppt) salinities. Unlike those juvenile barramundi reared at 45 ppt and 25% K-equivalence in the previous study, those reared in 50% K-equivalence water at 45 ppt in this study survived for four weeks but lost weight; whereas at 75% and 100% K-equivalences fish both survived and gained weight. Homeostasis of blood plasma potassium was maintained by buffering from skeletal muscle. Fish reared in 50% K-equivalence at this salinity exhibited muscle dehydration, increased branchial, renal and intestinal (Na+-K+)ATPase activity and elevated blood sodium and chloride, suggesting they were experiencing osmotic stress. At 15 ppt, equal rates of growth were obtained between all K-equivalence treatments. Buffering of plasma potassium by muscle also occurred but appeared to be in a state of equilibrium. Barramundi at 5 ppt displayed equal growth among treatments. At this salinity, buffering of plasma potassium from muscle did not occur and at 25% K-equivalence blood potassium was significantly lower than at all other K-equivalence treatments but with no apparent effect on growth, survival or (Na+-K+)ATPase activities. These data confirmed the hypothesis that proportionally more potassium is required at hyperosmotic salinities compared to iso- and hypo- osmotic salinities and also demonstrated that barramundi have a lower requirement for potassium than other marine and estuarine species being investigated for culture in inland saline groundwater. In addition to ongrowing fish, saline groundwater has potential for hatchery production. Specific advantages include the vertical integration of inland saline farms and the production of disease-free certified stock through isolation from the pathogens and parasites found naturally in coastal water. To determine the potential of utilizing inland saline groundwater for hatchery production, barramundi larvae were reared from 2 to 25 days post hatch in 14 ppt saline groundwater with either no potassium supplementation (38% K-equivalence) or full potassium supplementation (100% K-equivalence). Growth, survival and swimbladder inflation of these larvae were compared against those grown in control treatments of seawater (32 ppt) and seawater diluted to 14 ppt. Those reared in saline groundwater with 38% K-equivalence exhibited complete mortality within 2 days, whilst those held in groundwater with full supplementation survived at a rate equal to both control treatments (pooled average 51.1 ¡Ó 0.5%). At 25 days post hatch, there was no significant difference in larval length or dry weight between those grown in the 14 ppt control treatment and those in the saline groundwater with full potassium supplementation. There were no significant differences in swim bladder inflation between any of the surviving treatments (average 93.3 ¡Ó 2.5%). This is the first description of rearing barramundi larvae both in low salinity seawater and in saline groundwater, and demonstrates that the requirement for potassium by larval barramundi is higher than for juveniles of the same species. In addition to a deficiency in potassium, saline groundwater in Western Australia often contains an elevated concentration of manganese relative to seawater as a result of anaerobic reduction of manganese oxides or the pedogenic weathering of manganese-bearing rock. The effects of elevated manganese on marine or estuarine fish have not been described and a study was therefore conducted to determine if manganese, at a concentration typical of that found in saline groundwater, has any impact on fish. The effects of 5 mg/L of dissolved manganese on juvenile mulloway at salinities of 5, 15 and 45 ppt were determined by comparing the survival, growth and blood and organ chemistry with those grown at the same salinities without manganese addition. Survival of mulloway at 45 ppt in the presence of 5 mg/L of manganese (73 ¡Ó 13%) was significantly lower than all other treatments, which achieved 100% survival. Those fish grown in seawater without manganese exhibited rapid growth, which was not affected by salinity (SGR = 4.05 ¡Ó 0.29%/day). Those fish grown at 5 ppt and 45 ppt in the presence of manganese lost weight over the two week trial (SGR 0.17 ¡Ó 0.42 and -0.44 ¡Ó 0.83%/day, respectively), whilst those at 15 ppt gained only a small amount of weight (SGR 1.70 ¡Ó 0.20%/day). Growth was therefore affected by manganese and by the interaction of manganese and salinity, but not salinity alone. Manganese was found to accumulate in the gills, liver and muscle of the fish. No gill epithelial damage or other significant histological findings were found, however, significant differences in blood chemistry were observed. Blood sodium and chloride of manganese exposed fish were significantly elevated in hyperosmotic salinity (45 ppt) and depressed at hyposmotic salinity (5 ppt) compared with unexposed fish; consistent with manganese causing apoptosis or necrosis to chloride cells. Blood potassium was significantly elevated and liver potassium significantly reduced at all salinities in the presence of manganese. These findings are consistent with manganese interfering with carbohydrate metabolism. There were no differences in blood sodium, chloride or potassium across salinities in fish not exposed to manganese, demonstrating mulloway are capable of efficient osmoregulation across this salinity range.