Pr Hart

Effects of photoperiod, temperature and salinity on hatchery-reared larvae of the greenback flounder (Rhombosolea tapirina Günther, 1862)

Abstract The greenback flounder ( Rhombosolea tapirina ) is considered to have potential as an aquaculture species in southern Australia. Experiments were conducted to determine the optimal photoperiod, temperature and salinity for rearing of larvae through metamorphosis. Experiments were carried out in 31 tanks in a recirculating system. Optimal photoperiods were found to be 18–24h light, which increased the growth rate but had no effect on survival. Total darkness resulted in 100% mortality by Day 20 post-hatch. The optimal temperature for larval rearing was not clearly identified, but 19–20 °C gave better growth than lower temperatures. There were no clear temperature effects on survival trends over the range used, although 16 °C resulted in significantly lower survival than 17 or 19 °C. A salinity of 15‰ resulted in lower survival, compared with either 25 or 35‰, but there were no salinity effects on growth over the tested range.

EFFECTS OF SALINITY AND TEMPERATURE ON EGGS AND YOLK SAC LARVAE OF THE GREENBACK FLOUNDER (RHOMBOSOLEA TAPIRINA GUNTHER, 1862)

Abstract The greenback flounder ( Rhombosolea tapirina ) is considered to have potential as an aquaculture species in southern Australia. Experiments were conducted to determine the optimal salinity for fertilisation and buoyancy of eggs, the optimal temperature and salinity combination for incubation of eggs, and the optimal temperature for yolk absorption. Experiments were carried out in 25 and 200 ml beakers and 31 containers. Optimal fertilisation rates occurred at salinities of 35–45‰ and eggs were buoyant at salinities above 28‰. The optimal temperature for egg incubation was approximately 12 °C and salinity had no effect if maintained between 15 and 45‰. Yolk absorption appeared to be most efficient at 15 °C as this temperature resulted in the largest larvae at complete yolk absorption and the fastest growth rate. First feeding occurred at the end of yolk absorption but before the oil droplet was absorbed.

Growth of juvenile southern rock lobsters, Jasus edwardsii, is influenced by diet and temperature, whilst survival is influenced by diet and tank environment

Abstract The growth and survival of juvenile (2–15 g) southern rock lobsters (Jasus edwardsii) were examined under various culture regimes. In Experiment 1, lobsters held at ambient (13–18°C) or 18°C were fed either fresh mussels, a commercial prawn diet or a moist diet. Growth (specific growth rate (SGR)=1.2–1.32% BW day−1), survival (98%) and food conversion ratios (FCR=1.26–1.29) were significantly better (P 0.05), when the lobsters were fed mussels. There was a significant interaction (P 0.05). The high acceptance and good consumption rate of formulated diets is a positive first step in the development of commercial diets for southern rock lobsters. In Experiment 2, lobsters held at ambient (13–18°C) or 18°C were maintained in tanks containing hides, substrates or neither. Hides increased survival (98%, cf. 60–75%) (P>0.05), although they did not increase growth (P>0.05) compared to tanks without hides. The provision of a substrate to aid the lobsters in the moulting process did not prevent cannibalism. Lobsters grew significantly faster (P

Jaw development and malformation in cultured striped trumpeter Latris lineata

Intensive culture of striped trumpeter (Latris lineata) has resulted in a high incidence of jaw malformation in juveniles. In this study, cranial and jaw development in striped trumpeter was described in cultured larvae reared in greenwater on rotifers and Artemia. Jaw malformation was only evident in post-flexion larvae greater than the standard length of 10 mm and was characterised by an open jaw in which the maxilla and premaxilla were aligned dorso-ventrally, and the anterior hyoid arch elements were in an abnormal ventral position. X-radiography of the heads of juvenile and adult cultured striped trumpeter revealed ventro-lateral distortion of the jaw elements in comparison with wild-caught fish. The possible role of physical environmental factors and nutrition during culture are discussed in relation to jaw malformation in this and other species.

The effect of temperature on survival, growth, feeding and metabolic activity of the southern rock lobster, Jasus edwardsii.

This study investigated the effect of temperature (18, 20, 22 and 24°C) on growth, feeding and metabolism of post-puerulus lobsters as part of a larger study of the culture potential of farming the southern rock lobster, Jasus edwardsii. There was no significant difference (P>0.05) in the specific growth rates (SGR) at 18, 20 or 22°C; however, growth decreased significantly (P 0.05) in survival at 18, 20 or 22°C. The response of feed conversion ratio (FCR) to temperature was described by a quadratic regression (FCR=0.011T2−0.434T+5.231, r2=0.995), which suggested that the optimum temperature for feed conversion was 19.3°C. Oxygen consumption rates (MO2) increased with increasing temperatures between 18°C and 22°C and declined at 24°C; whilst total ammonia nitrogen (TAN) excretion increased with increasing temperature. The relationships were described by regression equations: MO2=−0.044T2+1.91T−18.553 (r2=1.0); TAN=0.127T−1.174 (r2=0.91). A temperature of 24°C appears to be above the upper thermal tolerance of juvenile J. edwardsii. Lobsters held at this temperature showed reduced survival (compared to those at 18°C), reduced growth (compared to those at 22°C) and appeared to be suffering from respiratory stress (moult-related mortalities, low Q10 between 22°C and 24°C). Overall, the results indicate that juvenile J. edwardsii can be cultured at 22°C without adversely affecting their growth, survival or feed efficiency with optimal temperature range between 19 and 21°C.

Lipids and nutrition of the southern rock lobster, Jasus edwardsii, from hatch to puerulus

We examined the lipid class and fatty-acid composition of the southern rock lobster, Jasus edwardsii, phyllosomas larvae and puerulus stage to improve understanding of their nutrition in relation to aquaculture. Lipid is critical in the nutrition of larval crustaceans, including lobsters. Specimens were from Tasmanian waters, Australia, and North Island, New Zealand, waters. Analyses were by TLC-FID and capillary GC and GC-MS. Phyllosomas larvae and nektonic pueruli were low in storage lipid (triacylglycerol), and phospholipid was the major lipid class. Sterol, mainly cholesterol, was the next most abundant class. The ratio of the essential omega-3 fatty acid eicosapentaenoic acid (EPA) to the omega-6 fatty acid arachidonic acid (AA) was lower in newly hatched phyllosomas (1.2-1.3) than in other phyllosomas (stages III-XI; 2.8-6.7) and pueruli (3.8). Ratios of the omega-3 fatty acid DHA (docosahexaenoic acid) to EPA were also lower in newly hatched phyllosomas (0.5) than in later-stage phyllosomas (1.5-2.1) and pueruli (1.2). We have followed up these compositional data by successfully enriching the live diet (Artemia) of early phyllosomas with AA, EPA and DHA. This dietary manipulation has achieved ratios of these key polyunsaturated fatty acids similar to those of wild phyllosomas. These findings will be of significance to the future of rock-lobster aquaculture.

Weaning of hatchery-reared greenback flounder (Rhombosolea tapirina Günther) from live to artificial diets: Effects of age and duration of the changeover period

The greenback flounder (Rhombosolea tapirina) is a potential culture species in Australia, but poor survival has been recorded during weaning from live Artemia to artificial diets. This paper describes the results of three experiments on the effects of fish age and the duration of the changeover period from live to artificial food on weaning survival and subsequent growth. Fish weaned for 10 days from Day 50 post-hatch or later had higher mortality (P 0.05) were observed between fish weaned on different days post-hatch. Weaning from Artemia to artificial diets was shown to be possible from Day 23 post-hatch, with 82.2% survival after a 10-day overlap. An overlap of 5 days between Artemia and artificial diets resulted in a reduction in final length (P 0.05). Overlaps of 20 days resulted in significantly heavier final weights (P < 0.05) than either 10 or 5 days. Weaning from Day 23 post-hatch with a 20-day overlap would therefore appear to result in the best growth and highest survival rate, but a 10-day overlap may result in reduced Artemia cost with minimal effect on performance.

Differences in egg quality between wild striped trumpeter (Latris lineata) and captive striped trumpeter that were fed different diets

Abstract This study assessed differences in egg quality between freshly caught striped trumpeter, Latris lineata , and captive striped trumpeter that were fed either chopped fish or commercial salmon pellets. Total lipid content of eggs did not differ between the three groups (average of 20% dry weight). The group fed chopped fish produced eggs with the greatest docosahexaenoic acid (DHA)/eicosapentaenoic acid (EPA) ratio (4:1) and, together with eggs collected from the wild group, contained the highest ratio of ( n −3)/( n −6) polyunsaturated fatty acids (PUFAs) (9:1 and 8:1, respectively). Ascorbic acid levels in eggs from the pellet-fed group (75 μg g −1 wet weight) were higher than eggs from the wild and chopped-fish groups (48 and 40 μg g −1 wet weight, respectively), but there was no difference in α-tocopherol content (average of 4.4 μg g −1 wet weight). The volume of eggs produced, fertilisation rate and length of the larvae at hatch did not differ, but the pellet-fed group produced eggs of greater diameter, which corresponded to a larger yolk volume, and higher hatching success than the wild group. Each group of broodstock produced viable eggs and yolk-sac larvae, but the relatively low DHA/EPA and ( n −3)/( n −6) ratios in the eggs from the pellet-fed fish suggest that this diet may be inferior, when compared to chopped fish, for sustained growth and survival.

Swim bladder malformation in hatchery-reared striped trumpeter Latris lineata (Latridae)

Abstract Swim bladder malformation is common in both larvae and later life stages of cultured striped trumpeter Latris lineata. This study used histology and gross morphology of whole larvae to describe the progression of abnormal development that proceeded initial liquid dilation of the primordial swim bladder. In addition, radiography was used to compare swim bladder morphology of cultured juveniles with wild-caught specimens. The histomorphology of the swim bladder prior to lumenal dilation was typical of transient physostome larvae reported in the literature. A distinct swim bladder lumen present in larvae between 5.2–5.7 mm standard length (SL) was assumed to be liquid dilated and coincided with mouth opening. Initial gaseous inflation was first apparent when larvae attained 5.7–6.2 mm SL, after the resorption of the yolk sac and oil globule and the onset of first feeding (

Enrichment of the rotifer Brachionus plicatilis fed an Antarctic bacterium containing polyunsaturated fatty acids

Abstract The Antarctic bacterium, strain ACAM 456, is known to produce eicosapentaenoic acid (20:5 n − 3, EPA). Following growth in batch culture, suspensions of this bacterium, at initial concentrations of 10 7 , 10 8 and 10 9 cells ml −1 , were used as foods for three respective cultures of the rotifer Brachionus plicatilis . At 6 and 24 h, rotifers were removed, harvested and extracted for analysis of fatty acid composition, which was compared to that of rotifers grown on bakers yeast. Incorporation of EPA, along with bacterial fatty acid markers (i13:0, i15:0 and 14:0), was evidenced at all bacterial food concentrations tested. The highest observed incorporation occurred when rotifers were grown in the medium initially containing 10 9 bacteria ml −1 . After 24 h of feeding, the level of EPA reached 9.4% of total fatty acids in the fed rotifers (6.7 ng of EPA rotifer −1 ). ACAM 456, a bacterial strain with the ability to produce EPA, was therefore shown to be a potential alternative enrichment food for the rotifer Brachionus plicatilis under feeding conditions that may be applicable to many Australian mariculture operations.