Year-Round Spawning, Filial Cannibalism, and Embryonic and Larval Development of the Coral Reef Fish Orchid Dottyback, Pseudochromis fridmani

Aquaculture of marine ornamental fish could potentially reduce the fishing pressure on wild stocks by the global aquarium trade, but its expansion is often constrained by the limited understanding on the biology and early life history of candidate species. The orchid dottyback Pseudochromis fridmani is a valuable and popular marine ornamental fish, but scientific reports on its baseline biology, especially the egg filial cannibalistic behaviour, are scarce. The present study documented key aspects of reproductive biology and early ontogeny of P. fridmani in captivity, including reproductive behaviour, patterns of spawning and filial cannibalism throughout a 12-month period by seven pairs of brood fish, as well as the embryonic and larval development. The results showed that the captive spawning of the broodstock pairs generally occurred every 5–11 days, most commonly every 6–8 days, throughout a year. Despite feeding the brood fish to satiation throughout the data collection period, the average monthly rate of egg filial cannibalism reached 55 ± 37%, but the cannibalism frequency appeared to be pair-specific. The egg incubation duration was approximately 96 h at 27 ± 1 °C, and the development of embryos from cleavage, blastula, gastrula, and segmentation to the pharyngula stage is herein described in detail. The newly hatched P. fridmani larvae possessed important structures and organs for first feeding, including pigmented eyes, developed jaws, and a straight-tube gut. The 0 to 14 days post-hatching (DPH) period appeared to be an important larval stage, as P. fridmani larvae were observed to complete major changes in morphology, gut development, and phototactic behaviour by 14 DPH. Under the culture conditions of this study, the earliest transition to the juvenile stage was observed on 31 DPH, and the majority of fish became juveniles by 56 DPH. The results of this study inform baseline aquaculture production protocols and direct future research, particularly to reduce filial cannibalism through broodstock management and to improve larval culture through supporting the early ontogenetic development of P. fridmani. Additionally, these findings form a foundation for further studying the biology and ecology of P. fridmani in the wild

Visual field of cultured striped trumpeter Latris lineata (Teleostei) larvae feeding on rotifer prey

The visual field of striped trumpeter Latris lineata larvae fed rotifer prey was determined from analysis of feeding behaviour in the horizontal plane. The visual field was forward and laterally directed, characterised by maximum reactive distances (distance at which the predator first detects and reacts to the prey) of 5.07 mm and 5.25 mm on days 13 and 17 post-hatching, respectively, 97% of mean larval length. This confirmed the predicted horizontal visual field, forward and laterally directed, derived from higher cone cell densities in the dorso-temporal and medial regions of the retina compared with ventral regions. The visual field of prey detection expanded laterally with ontogeny as a wider range of reactive angles was used by 17 day-old than 13 day-old larvae. Larvae displayed a saltatory searching pattern, periodically stopping to scan for prey throughout the visual field, and exhibited a side-to-side movement of the head as they approached and stopped, prior to striking at a detected prey item. Larvae on day 17 post-hatching terminated 35% of feeding sequences at the pre-strike position, at a mean distance from prey of 0.58 mm

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

Digestive system ontogeny and the effects of weaning time on larval survival, growth and pigmentation development of orchid dottyback Pseudochromis fridmani

Although live prey remain essential for most marine finfish larviculture, the larvae or young juveniles are ultimately weaned onto formulated feeds at foodfish and ornamental fish hatcheries. Understanding the development of larval digestive capabilities is crucial for optimizing weaning success. The present study used the digestive system ontogeny to interpret the effects of different weaning times on larval rearing of orchid dottyback Pseudochromis fridmani, a marine ornamental fish species. The study documented the ontogenetic digestive system development of P. fridmani larvae from hatching to 40 days post-hatching (DPH). The histological analysis showed that as a demersal spawning species, the newly hatched P. fridmani larvae possessed advanced gut development which allowed the onset of exogenous feeding soon after hatching. Most major larval gut morphological changes were completed by 13 DPH; however, the stomach and gastric glands were first observed between 32 and 36 DPH. At this stage, P. fridmani larvae were expected to acquire substantially improved digestive capabilities, and were likely capable of digesting formulated feed. In the subsequent experiment, P. fridmani larvae were weaned onto formulated feed from 20, 23, 26, 29, or 32 DPH over a three-day period of co-feeding with enriched Artemia; the control group were exclusively fed enriched Artemia until the end of experiment. The timing of weaning significantly affected the larval growth and pigmentation development rather than survival (mean: 44-64%). P. fridmani larvae weaned later tended to grow larger, and the control group grew significantly larger in length than all weaning treatments (p < 0.05). Interestingly, at the end of the experiment (40 DPH), none of larvae from the control obtained adult-type pigmentation despite their larger size. In contrast, the introduction of formulated feed appeared to stimulate pigmentation development in P. fridmani individuals with a clear trend of higher pigmentation completion by 40 DPH (mean: 62-97%) with earlier weaning. Overall, this study demonstrated that P. fridmani larvae could be weaned onto formulated feed from as early as 20 DPH, before the stomach and gastric glands were fully developed; indeed, the timing of adult-type pigmentation change in P. fridmani was also advanced by the introduction of the weaning diet

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

Jaw malformation in cultured yellowtail kingfish (Seriola lalandi) larvae

Several jaw malformations are common in cultured finfish larvae. Hatchery-reared yellowtail kingfish (Seriola lalandi) larvae were cleared and stained to examine cartilage and bone structure of the jaw. One malformation, characterised by a lowered hyoid arch, was present in kingfish larvae on days 4 and 8 post-hatching, but not on day 12. A different malformation was present in larvae on day 16, typified by abnormal positioning of the lowerjaw and hyoid arch, and breakage of the Meckel's cartilage. Evidence of jaw malformations as early as day 4 suggests that broodstock nutrition may be a factor in the jaw malformation of kingfish larvae, but other potential causes are environmental factors in culture and larval nutrition

Advances in practical feed formulation and adoption for hybrid grouper (Epinephelus fuscoguttatus ♀ × E. lanceolatus ♂) aquaculture

Grouper aquaculture is currently trending towards production of hybrids, due to their improved growth and disease resistance. The predominant cross is between tiger grouper (Epinephelus fuscoguttatus) females and giant grouper (Epinephelus lanceolatus) males (TGGG). Sustainable TGGG aquaculture development is limited by reliance on wild-caught ‘trash’ fish as feed rather than commercially formulated feeds. Specific TGGG nutrient requirement values remain limited, especially for larger fish that consume the highest volumes of feed. This limits the effectiveness of formulated feeds to provide optimal growth and feed conversion in an economically efficient manner. This review examines the current knowledge of hybrid grouper nutrient requirements for grow-out feeds and identifies knowledge gaps to inform further research that will enable development of cost-effective feeds that optimize fish growth, feed conversion and health. Current best practice in TGGG feeds specifies a relatively high protein requirement (53.5% crude protein), with higher arginine and lower lysine requirements than previously reported for grouper species. Like other groupers, the hybrid appears to require low lipid levels (10–14%); however, it remains to be elucidated whether this increases significantly with body size. The nutrient requirement data within this review provide a starting point for development of specific hybrid grouper feeds. However, commercialization of such feeds requires better understanding of the socio-economic context of the target industry. While formulated feeds may be more cost-effective, their implementation is limited by inferior growth compared with ‘trash’ fish. Performance gains are expected through increased understanding of size-specific nutrient requirements and specific raw material quality criteria

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