Skeletal malformations in Australian marine finfish hatcheries

The Australian finfish aquaculture industry has a target to more than treble production from 2005 to 100,000 t p.a. by 2015. Most of the current production is from sea cage culture of Salmo salar and Thunnus maccoyii but new and emerging species are predicted to have a faster increase in production and were the focus of this study. The quantity and quality of hatchery-produced fingerlings is an impediment to achieving growth in the marine finfish sector. A survey of 18 hatcheries revealed that 44% indicated skeletal malformations were a significant issue in hatchery production, and 89% reported variability in malformation rates between production batches. Samples of fish from selected hatcheries were cleared and stained for assessment of abnormal bone development. Two hatcheries that had indicated malformations were not a significant problem submitted samples with >5% severe malformations. Jaw and spinal malformations occurred in Lates calcarifer, Seriola lalandi, Epinephelus fuscoguttatus, E. coioides, and Latris lineata. To the best of our knowledge, causative factors of malformations in Australian hatcheries have only been identified for jaw malformation in Lates calcarifer and Latris lineata, and further research is either needed or underway with other species and malformation types in order to improve culture protocols and increase fingerling quality. Improved monitoring techniques for skeletal malformations would substantially enhance the comparison of production methods at a commercial scale and enhance research efforts

The first-feeding response of larval southern bluefin tuna, Thunnus maccoyii (Castelnau, 1872), and yellowtail kingfish, Seriola lalandi (Valenciennes, 1833), to prey density, prey size and larval density

We investigated the first-feeding success of two species: southern bluefin tuna (Thunnus maccoyii) and yellowtail kingfish (Seriola lalandi) to determine if similar culture parameters can be used for both, especially when S. lalandi are held in the same tanks as prey for T. maccoyii. The feeding performance (proportion and intensity) was examined in three short-duration (4h) experiments: prey density, prey size and larval density. Increasing prey density from 0.5 to 25 rotifersmL(-1) increased the proportion of T. maccoyii and S. lalandi larvae feeding. Prey size alone did not affect feeding in either species. Seriola lalandi had a decreased proportion of larvae feeding when larval density reached 50 larvaeL(-1) concurrent with a gradual increase in feeding intensity between 2 and 50 larvaeL(-1). In T. maccoyii, there was no pattern to the effect of larval density on the proportion of larvae feeding. The overall feeding performance of larvae was higher in T. maccoyii than S. lalandi. Increased prey density improved the first-feeding ability of T. maccoyii and S. lalandi larvae. The effect of larval density on S. lalandi feeding requires further investigation, to ensure that they remain feeding when provided as prey in T. maccoyii culture. The identification of factors in this study, which increase first-feeding success, will improve the culture of both species

Parasitic crustaceans infecting cultured striped trumpeter Latris lineata

Cultured striped trumpeter Latris lineata was held in sea cage systems or a land-based facility in south-eastern Tasmania. Visual checks of metazoan ectoparasites were conducted on six cohorts (T1 to T6) in the land-based facility from 2006 to 2007, and three cohorts (C1 to C3) held in cages from 2007 to 2008. Three parasite species were recorded; a cymothoid Ceratothoa banksii; a chondracanthid Chondracanthus goldsmidi; and a caligid Caligus nuenonnae. All three parasite species were present on the striped trumpeter in the sea cages with C. nuenonnae and C. goldsmidi found in very low prevalence on all cohorts. There was no significant effect of cohort or season on the parasites' prevalence or intensity. Cohort C1 had the highest numbers of C. nuenonnae with prevalence of 2.5% (intensity 1.0 +/- 0.0 parasites fish(-1)), whilst cohort C3 had the highest prevalence of C. goldsmidi (3.3%, intensity 1.0 +/- 0.0). The isopod C. banksii was recorded in increasing prevalence in cohorts C1 and C2 during 2008, cohort C1 had a prevalence ranging from 9.8% (intensity 1.0 +/- 0.0) to 17.5% (intensity 1 +/- 0.0) whereas prevalence in cohort C2 ranged from 27.7% (intensity 1.21 +/- 0.1) to 67.2% (intensity 1.8 +/- 0.1). The two copepod species were recorded on the fish held in the land-based facility. C. nuenonnae was found on fish from two cohorts at a prevalence of 22.3% (intensity 1.4 +/- 0.1 parasites) in cohort T1 and 4.3% (1.0 +/- 0.0) in cohort T2. In contrast, C. goldsmidi was present during all parasite checks of cohorts T2 to T6 with the percentage of infected fish ranging from 27.2% (intensity 1.3 +/- 0.1) in cohort T2 to 100% (intensity 32.8 +/- 1.9) in cohort T4. Treatments against C. goldsmidi were conducted on cohorts T2 to T6 including manual removal of adult parasites and Neguvon baths. There was no apparent reduction in the parasite prevalence within season during follow-up surveys after +/- 6 months. An eleven month re-infection experiment was conducted with C. goldsmidi; striped trumpeter from which parasites were removed showed significantly lower prevalence (F = 161.8, df (1,20), P < 0.001) than those fish from which parasites were not removed. The study suggests that effective control of parasitic crustaceans is likely to be an important factor in the successful culture of sea-caged striped trumpeter

The effects of tank colour, live food enrichment and greenwater on the early onset of jaw malformation in striped trumpeter larvae

A high incidence of jaw malformation has hindered the production of quality striped trumpeter Latris lineata juveniles and has been correlated with walling behaviour in Artemia-fed larvae. In this study, striped trumpeter were reared from first feeding to 29 days post-hatching (dph) in different coloured tanks (black or white), culture conditions (clear or greenwater) and fed different diets (enriched or non-enriched rotifers and Artemia), to examine behaviour, retinoid receptor gene expression and jaw malformation. The highest incidence and severity of jaw malformations occurred in clearwater and enriched diet treatments and were significantly more common in white (70 +/- 15%, mean +/- SD) than in black tanks (26 +/- 15%). In black tanks, jaw malformation was significantly more common in larvae fed enriched diets (18 +/- 14%) than in those fed non-enriched diets (8 +/- 8%) and in clearwater (19 +/- 14%) versus greenwater (7 +/- 6%). At the end of the rotifer feeding phase, larvae were significantly larger in black than white tanks, and longer in greenwater than in clearwater. In the Artemia feeding phase, larval growth was slowest and mortality was highest in non-enriched diet treatments. Larval length and survival were higher in black tanks and in enriched diet treatments, whilst survival was almost twice as high in greenwater (46 +/- 18%) than clearwater (26 +/- 13%). The average proportion of larvae walling over the duration of the experiment was higher in white than black tanks, and higher in enriched than non-enriched treatments, with lowest walling in greenwater. There was no consistent relationship between feed intake and jaw malformation. However, there was a significant positive correlation between walling and the incidence of jaw malformation at 29 dph in larvae fed enriched diets. The expression pattern of three retinoid receptor genes indicated that live feed enrichment and stress could potentially perturb retinoic acid-associated pathways leading to skeletal abnormality. We found that the use of greenwater, black tanks and enriched live feeds is required for good growth, development, survival and final yield of striped trumpeter. The study emphasises the importance of reducing walling in the culture of oceanic larvae and may have direct application in the rearing of other marine fish with similar malformations

Retinal adaptations of southern bluefin tuna larvae: implications for culture

We examined Southern bluefin tuna, Thunnus maccoyii, larvae to identify specific retinal adaptations that would indicate both important parameters for culture and larval ecology in the wild. Plastic resin histology, microspectrophotometry and behavioural feeding responses were used to describe visual development. Thunnus maccoyii larvae reflected the visual morphogenesis template commonly observed in many other marine fish species exhibiting indirect development. First-feeding (3 days post-hatching, [dph], 3.4mm standard length [SL]) larvae possessed tightly packed single cone photoreceptors. Rods and twin cones were present in the retina in post-flexion larvae (21 dph, 8.39mm fork length [FL]) with cone mosaic patterns observed in juveniles (30 dph, 21mm FL). Based on the spacing of adjacent photoreceptors and focal length, first feeding larvae had a maximum theoretical visual acuity of 1.23 ± 0.11° that decreased to 0.14 ± 0.02° at 30 dph. Thunnus maccoyii displayed high cell density in the ventral retinal region (cones, bipolar and horizontal cells), a low convergence of cone cells to ganglion cells throughout the retina during larval development (1.1 ± 0.2 to 1.4 ± 0.3 at 3 dph and 30 dph, respectively), and early development of retinal pigment epithelium (RPE) migration. Microspectrophotometry showed twin cone visual pigments maximally sensitive to light in the blue-green part of the visual spectrum (wavelength of maximum absorption [λmax] of 494 nm, 507 nm and 524 nm), and behavioural experiments showed they fed preferentially at these wavelengths. Increased retinal cone densities in the ventral region indicated a localized region specialized for acute vision for prey and predator detection in the upward direction (dorsal plane) at an early age, representing a possible adaptation to life in deeper oceanic waters. The apparent high acuity and photopic sensitivity observed in T. maccoyii is hypothesised to be associated with the ability to feed in low light conditions. This has important practical considerations in determining lighting regimes for culture of T. maccoyii and possibly for other tuna species