Sc Battaglene

Daily burrowing cycle and feeding activity of juvenile sea cucumbers Holothuria scabra in response to environmental factors

This study investigated the daily activities of juvenile sea cucumbers Holothuria scabra Jaeger. All individuals exhibited daily burrowing and feeding rhythms in response to environmental factors. The cycle of the smallest juvenile, >10–40 mm, was linked to light; they began to burrow around sunrise and emerged close to sunset. Their burrowing activity was inhibited by continuous darkness. Juveniles >40–140 mm responded to changes in temperature; they burrowed earlier around 03:30 h, seeking shelter in the sediment as temperature declined, and emerged around mid-day. The maintenance of a constant warm temperature prevented them from burrowing. For all juveniles, time spent on the surface corresponded with feeding and periods of locomotion; while burrowed they remained stationary, did not feed and had a low intestinal transit. Organic matter content in the intestine was also found to vary with the daily cycle. Decreases in salinity from 35 to 30, 25 and 20‰ induced the burrowing of all juveniles within minutes, but they began to re-emerge after a few hours. Acclimation occurred most rapidly at salinity 30‰ and was slowest at salinity 20‰. Conversely, nearly 40% of the juveniles were unable to cope with a decrease to salinity 15‰. Juveniles of all sizes demonstrated a strong selectivity for sediment characteristics. In two substrate selection experiments, their preference for sand with a grain size around 0.4 mm and for organically rich material was firmly expressed within an hour. The general behavior of juvenile H. scabra reflects their ability to inhabit shallow sandy areas with high terrigenous inputs and variable environmental conditions.

Settlement preferences and early migration of the tropical sea cucumber Holothuria scabra.

Settlement and post-settlement processes of the sea cucumber Holothuria scabra Jaeger were studied in the laboratory. Independent and paired choice experiments revealed that several substrates could induce metamorphosis into pentactulae, but that specific substrates favoured settlement. Leaves of seagrass Thalassia hemprichii, with or without their natural bio-film, yielded the highest settlement rates (4.8-10.5%). T. hemprichii was preferred as a settlement substrate over sand, crushed coral, several other plant species and artificial seagrass leaves with or without a bio-film. Only settlement on the seagrass, Enhalus acoroides, was similar to that recorded for T. hemprichii. In the absence of a substrate, the larvae delayed settlement for nearly 96 h and survival was less than 0.5%. Sand and crushed coral, either alone or together, induced settlement from <1.5% of the available larvae. The pentactulae found on sand, coral and in bare containers were 10-35% smaller than those on T. hemprichii leaves. Soluble extracts from T. hemprichii and E. acoroides successfully induced metamorphosis and settlement on clean plastic surfaces. Newly settled juveniles remained on the seagrass leaves for 4-5 weeks before migrating to sand at around 6 mm in length. Prior to this, the juveniles spent 4-5 days moving on and off the leaves. Once on the sand, the juveniles became deposit-feeders, but did not show the typical burrowing behaviour of older specimens until they reached around 11 mm in length. The larvae of H. scabra appear to actively select seagrass leaves, possibly through chemical detection. We hypothesise that larvae settling on seagrass have an increased chance of growth and survival because they are provided with a suitable substrate on which to grow, and a bridge to sand substrates as they become deposit-feeders.

Periodic movement, recruitment and size-related distribution of the sea cucumber Holothuria scabra in Solomon Islands

Field studies of the sea cucumber Holothuria scabra conducted in Kogu Veke, Solomon Islands, showed monthly recruitment of newly-settled juveniles on seagrass and indicated that size distribution was a function of substratum type and depth. Adults >250 mm body length were found mainly on sand, with <5% organic matter (OM), at depths of >1–3 m. Individuals >10–250 mm were found mostly in 30–120 cm of water, on mud and muddy sand with OM content between 5 and 10%. Specimens >40–150 mm were also found in the intertidal zone, sometimes burrowed on exposed sandflats at low tide. Holothuria scabra avoided substrata of fine silt or shell and coral pebbles, and sediment with an organic content ≥30%. Juveniles ≤100 mm burrowed at sunrise and surfaced at sunset, whereas individuals >100 mm burrowed and surfaced a few hours earlier. Holothuria scabra tended to burrow when salinity decreased, whereas increased water temperatures reduced normal burrowing behaviour. Spatial distribution, observed during tank experiments, suggested that adult H. scabra aggregated prior to spawning and in response to the lunar cycle. The formation of pairs, trios or larger groups increased during the new moon and was most common just before the full moon. Newly-settled juveniles up to ca. 9 mm were found on seagrass leaves. Typically, maximum densities and smallest recruits were observed a couple of weeks after the full moon, lower densities and slightly larger recruits were found a few days later. Juveniles with a mean length around 65 mm released on sand moved less and grew faster than juveniles released in seagrass beds or on substrata of shells and crushed coral.

Effects of photoperiod and light intensity on initial swim bladder inflation, growth and post-inflation viability in cultured striped trumpeter (Latris lineata) larvae

Transient physostomes often fail to complete initial swim bladder inflation in culture and display reduced survival and growth. Three experiments were conducted in replicate 200-l tanks to determine the effects of photoperiod and light intensity on initial swim bladder inflation, postinflation viability (surviving larvae with inflated swim bladders) and growth in striped trumpeter (Latris lineata) larvae. Both photoperiod and light intensity were found to affect initial swim bladder inflation, growth, survival and post-inflation viability of striped trumpeter larvae. Higher initial swim bladder inflation was promoted by providing a dark-phase before and during initial swim bladder inflation. Swim-up behaviour where larvae gulped air at the water surface to fill their swim bladder was predominantly observed during the dark-phase. In Experiment 1, a 12L:12D photoperiod was inferior to either a 18L:6D or 24L:0D photoperiod for larval growth. In Experiment 2, initial swim bladder inflation was higher in larvae reared under a light intensity of 4 Amol s 1 m 2 compared to 40 Amol s 1 m 2. From Experiment 3, a 18L:6D photoperiod provided higher post-inflation viability than either 24L:0D, or a photoperiod combination of 24L:0D from stocking, changing to 21L:3D at the onset of initial swim bladder inflation. However, different optimal photoperiods for initial swim bladder inflation (18L:6D) and survival (24L:0D) lowered post-inflation viability in

Cloning and expression analysis of three striped trumpeter (Latris lineata) pro-inflammatory cytokines, TNF-α, IL-1β and IL-8, in response to infection by the ectoparasitic, Chondracanthus goldsmidi.

This study reports the cloning and sequencing of three striped trumpeter (Latris lineata Forster) pro-inflammatory cytokines, TNF-alpha, IL-1beta and IL-8, as well as their differential expression in response to an infection by the ectoparasite Chondracanthus goldsmidi. The striped trumpeter TNF-alpha transcript consisted of 1093 bp, including a 759 bp ORF which translated into a 253 aa transmembrane peptide. The sequence contained a TACE cut site, that would produce a 167 aa soluble peptide containing the TNF ligand family signature. The IL-1beta sequence consisted of 963 bp, including a 774 bp ORF which translated into a 258 aa protein. The protein lacked both a signal peptide and an ICE cleavage site, but did contain the IL-1 family signature. The sequence for the chemokine IL-8 contained 906 bp, with an ORF of 297 bp, which translated into a 99 aa protein. The protein lacked an ELR motif as is common with many teleost IL-8 sequences. The differential expression of the three cytokine genes in parasitized fish was investigated via quantitative real-time PCR. A significant up-regulation of all three pro-inflammatory cytokines was found in the gills, which were the site of parasite attachment. Examination of head kidney cells revealed a significant up-regulation of TNF-alpha, but not IL-1beta or IL-8. Conversely, the spleen cells showed significant up-regulation of both IL-1beta and IL-8, but not TNF-alpha. These findings allow for more detailed investigations of the striped trumpeter immune response.

Spawning induction of three tropical sea cucumbers, Holothuria scabra, H. fuscogilva and Actinopyga mauritiana

Tropical sea cucumbers, Holothuria scabra, H. fuscogilva and Actinopyga mauritiana were collected from the wild, held in insulated containers and transported by a combination of sea, air and road transport for up to 12 h. Methods for obtaining reliable supplies of fertilised eggs from wild-caught broodstock were investigated. Of the 779 H. scabra collected, 4.5% eviscerated during transport, compared with 11.0% of the 181 H. fuscogilva and none of the 52 A. mauritiana. Experiments conducted in 20-l containers, with and without sea water and temperature control, determined that H. scabra survived for over 80 h, H. fuscogilva for 8 h and A. mauritiana for 20 h, in static seawater at 29 °C. Spawning of H. scabra in Solomon Islands can be induced throughout the year, but only in 3 months for H. fuscogilva (from August to October), and 2 months for A. mauritiana (from October to November). The peak spawning period for all three species was during the dry season: August–November. Collection, transport and thermal stress was an effective spawning induction method for H. scabra and A. mauritiana. Induced egg production in H. scabra was greatest in September, when 35% of broodstock spawned. Spawning appeared to be entrained to a lunar cycle in H. scabra, and occurred more readily during the afternoon and early evening. Addition of dried Schizochytrium sp. induced spawning in H. fuscogilva and was far more effective than thermal induction. Females of all three species were highly fecund and capable of multiple spawning. The mean number of fertilised eggs was: 1.9 million (±0.6 S.E., n=17) for H. scabra; 2.6 million (±0.2 S.E., n= 5) for H. fuscogilva and 2.6 million (±0.1 S.E., n=6) for A. mauritiana. The techniques for inducing spawning identified in this study allowed the collection of fertilised eggs for experimental and pilot-scale mass production of juvenile sea cucumbers. Further research should target improved spawning induction through the conditioning and holding of captive broodstock.

Analysis of the central nervous system transcriptome of the eastern rock lobster Sagmariasus verreauxi reveals its putative neuropeptidome.

Neuropeptides have been discovered in many arthropod species including crustaceans. The nature of their biological function is well studied and varies from behavior modulation to physiological regulation of complex biochemical processes such as metabolism, molt and reproduction. Due to their key role in these fundamental processes, neuropeptides are often targeted for modulating these processes to align with market demands in commercially important species. We generated a comprehensive transcriptome of the eyestalk and brain of one of the few commercially important spiny lobster species in the southern Hemisphere, the Eastern rock lobster Sagmariasus verreauxi and mined it for novel neuropeptide and protein hormone-encoding transcripts. We then characterized the predicted mature hormones to verify their validity based on conserved motifs and features known from previously reported hormones. Overall, 37 transcripts which are predicted to encode mature full-length/partial peptides/proteins were identified, representing 21 peptide/protein families/subfamilies. All transcripts had high similarity to hormones that were previously characterized in other decapod crustacean species or, where absent in crustaceans, in other arthropod species. These included, in addition to other proteins previously described in crustaceans, prohormone-3 and prohormone-4 which were previously identified only in insects. A homolog of the crustacean female sex hormone (CFSH), recently found to be female-specific in brachyuran crabs was found to have the same levels of expression in both male and female eyestalks, suggesting that the CFSH female specificity is not conserved throughout decapod crustaceans. Digital gene expression showed that 24 out of the 37 transcripts presented in this study have significant changes in expression between eyestalk and brain. In some cases a trend of difference between males and females could be seen. Taken together, this study provides a comprehensive neuropeptidome of a commercially important crustacean species with novel peptides and protein hormones identified for the first time in decapods.

Swim bladder inflation in larvae of cultured sand whiting, Sillago ciliata Cuvier (Sillaginidae)

Abstract Failure of the swim bladder to inflate can cause mortality in intensively cultured marine fish larvae. Surface access and light intensity are two key factors which influence inflation. Sand whiting ( Sillago ciliata ) have a diel pattern of nocturnal swim bladder inflation in the wild. The objectives of this study were to determine when initial swim bladder inflation starts in cultured S. ciliata larvae, if surface access is required, and the effects of light. S. ciliata was found to inflate the swim bladder at night and completely deflate it during the day. This pattern starts on day 4, when the mean larval length is 2.8 mm and coincides with the completion of yolk sac and oil globule absorption, the start of exogenous feeding, and heavy larval mortality. Maximum swim bladder volume in 5-day-old larvae peaks 2 h after dusk and then gradually declines before dawn. The diel pattern of nocturnal inflation continues until day 17 when increasing numbers of larvae (mean length 6.4 mm) retain partially inflated swim bladders during the day. Experiments with 12-, 15- and 19-day-old larvae, siphoned into 2-litre beakers at midday, show that larvae respond to darkness by inflating their swim bladders. Placing oil on the surface of darkened beakers did not prevent swim bladder inflation in larvae from day 12. Swim bladder volumes were small and not significantly different for larvae in beakers with low light (413 lx) and high light (1360 lx). However, significant differences in feeding were observed with larvae, under high light, eating more rotifers than larvae in low light. Larvae did not feed in the dark. It is proposed that nocturnal swim bladder inflation allows S. ciliata larvae to conserve energy at night when they are not feeding. Although S.ciliata larvae have a different swim bladder inflation pattern from that of most species, it is suggested that it will present few additional culture problems. A light intensity of 1000–1500 lx, and a constant photoperiod are recommended to maximise swim bladder inflation.

Hormone induction and larval rearing of mulloway, Argyrosomus hololepidotus (Pisces: Sciaenidae)

Abstract Pond-held mulloway ( Argyrosomus hololepidotus ) from Port Hacking, New South Wales, were induced to spawn by injecting human chorionic gonadotrophin (hCG) at 1000 IU/kg for females and 250 IU/kg for males. Two pairs of fish were stripped, and fertilised eggs were incubated at 23.5±1°C. Fecundity was high with an estimated 900 000 and 1 042 000 eggs collected from each female. At hatch, larvae averaged 2.25 ± 0.09 mm TL (mean ± s.d.) with a yolk sac of 0.88 ± 0.08 mm and an oil globule of 0.27±0.03 mm. Feeding and initial swim bladder inflation started between day 3 and 4 after hatch. Metamorphosis started when larvae reached 12 mm at 23 days of age, and was complete by day 34 when larvae were 15–26 mm. Larvae with functional swim bladders (>70% by day 11) grew faster than those without swim bladders. Cannibalism of smaller fish, many without swim bladders (4.2±0.06 mm), occurred from day 18. Fish were offered live food to day 68, supplemented with finely chopped pilchards and pellets from day 38. From day 106 to day 180 fish were feeding solely on pellets. Juveniles grew to a mean weight of 21.0±0.7 g and a mean length of 121.5±1.3 mm in 180 days. These results indicate that A. hololepidotus has potential for hatchery production.

Discovery of a novel insulin-like peptide and insulin binding proteins in the Eastern rock lobster Sagmariasus verreauxi.

This study reports, for the first time in any of the commercially important decapod species, the identification of an insulin-like peptide (ILP), distinct from the androgenic gland hormone. Bioinformatics analysis of the de novo assembled spiny lobster, (Sagmariasus verreauxi) transcriptome, allowed identification of Sv-ILP1 as well as eight binding proteins. Binding proteins were termed as Sv-IGFBP, due to homology with the vertebrate insulin-like growth-factor binding protein and Sv-SIBD1-7, single insulin-binding domain protein (SIBD), similar to those identified in other invertebrate species. Sv-ILP1 was found to be expressed in the eyestalk, gonads and antennal gland of both sexes and to a lesser extent in male muscle, androgenic gland and hepatopancreas. The expression profiles of each binding protein were found to vary across tissues, with Sv-SIBD5, 6 and 7 showing higher expression in the gonad, demonstrated by PCR and digital gene expression. Further spatial investigations, using in-situ hybridisation, found Sv-ILP1 to be expressed in the neurosecretory cells of the thoracic ganglia, in keeping with the tissue expression of Drosophila ILP7 (DILP7). This correlative tissue expression, considered with the phylogenetic clustering of Sv-ILP1 and DILP7, suggests Sv-ILP1 to be a DILP7 orthologue. The broad expression of Sv-ILP1 strongly suggests that ILPs have a role beyond that of masculinisation in decapods. The function of these novel peptides may have application in enhancing aquaculture practices in the commercially important decapod species.