Evaluation of tuna by‐product meal as a protein source in feeds for juvenile spotted rose snapper Lutjanus guttatus

This study evaluated the use of tuna by‐product meal (TBM), a locally produced feed ingredient, as a replacement for fish meal (FM) in diets for spotted rose snapper, Lutjanus guttatus. Six isonitrogenous compounds [480 kg^?1 crude protein (CP) and isoenergetic diets (21 kJ g^?1)] were formulated to replace 0 (D‐0%), 10 (D‐10%), 20 (D‐20%), 30 (D‐30%), 40 (D‐40% or 50% (D‐50%) of FM protein with TBM protein. Each diet was fed to four replicate groups of spotted rose snapper (initial weight 5.4 g ± 0.04 g) to apparent satiation three times a day. After 8 weeks of feeding, the fish gained 4–5 times their initial weight. Spotted rose snapper fed D‐30% had a significantly higher specific growth rate (2.7% day^?1) than fish fed the other diets containing lower or higher amounts of TBM. Haematological parameters and whole‐body proximate composition were unaffected by diet (P > 0.05). The ADC for protein and energy in D‐0%, D‐20% and D‐30% were significantly higher than those for the D‐40% and D‐50% groups. A broken line model indicated that 262 g kg^?1 TBM in the diet would yield maximum growth of the spotted rose snapper. The results of this study demonstrate that TBM is an acceptable ingredient for replacing 25–30% of dietary protein from FM in spotted rose snapper diets but that higher replacement levels reduce fish performance.     

The potential of pet‐grade poultry by‐product meal to replace fish meal in the diet of the juvenile spotted rose snapper Lutjanus guttatus (Steindachner, 1869)

A 12‐week feeding trial was conducted to examine the replacement of fish meal with pet‐grade poultry by‐product meal (PBM‐PG) in the spotted rose snapper Lutjanus guttatus diet. Five experimental diets were formulated to contain graded levels of PBM‐PG at proportion of 250, 500, 75 or 900 g kg^?1. The control diet contained sardine fish meal as the main protein source. Four groups of 15 randomly assigned L. guttatus juveniles were fed to satiation 3 times day^?1. Except for the fish fed the PBM‐PG90 diet, the growth performance, survival and feed utilization efficiency of the experimental fish were not significantly lower than those of the control fish. The dietary level of PBM‐PG did significantly affect the haematological characteristics (P < 0.05). The dietary dry matter and protein apparent digestibility coefficients (ADCs) decreased with increasing dietary PBM‐PG. High values for lipid ADCs were observed in all diets, with significant differences among the dietary treatments. The fish whole‐body protein, moisture, lipid and ash contents were not affected by the inclusion of dietary PBM. These results indicate that high‐quality terrestrial PBM can successfully replace more than half of the marine fish meal protein in the L. guttatus diet.     

Nutrition and feeding research in the spotted rose snapper (<Emphasis Type="Italic">Lutjanus guttatus</Emphasis>) and bullseye puffer (<Emphasis Type="Italic">Sphoeroides annulatus</Emphasis>), new species for marine aquaculture

The spotted rose snapper (Lutjanus guttatus) and bullseye puffer (Sphoeroides annulatus) are fish species from the tropical Eastern Pacific for which controlled production of larvae and juveniles has been accomplished in recent years. Diverse topics relating to their biology and aquaculture production are currently under study, in particular the nutrition and feeding aspects required to formulate practical feeds and rearing protocols. Improvements in larval growth and survival are possible by feeding live food organisms with natural or enhanced essential fatty acids content and highly digestible artificial microdiets. The ontogeny of the digestive tract and the expression and activity of digestive enzymes have been described for S. annulatus larvae. The effect of various protein and lipid levels on growth and feed utilization has been studied in juvenile and on-growing fish. Both species have carnivorous feeding habits and require high levels of protein in their diets, from 40% to 45% (dry weight) in spotted rose snapper and above 50% in bullseye puffer, with the younger stages requiring the highest protein levels. Encouraging results have been obtained in feeding experiments with different sources of dietary protein from animal and plant origin to evaluate their suitability as feed ingredients in practical diets. Optimization of fish culture practices through feeding management has also been investigated. Trials with various fish densities and feeding frequencies in intensive culture systems are providing information to improve feed utilization and growth in on-growing fish. Further research is underway to evaluate factors in broodstock nutrition which have an impact on egg and larval quality, and into the use of various commercially available oil sources in on-growing diets. In this paper, the results on nutrition and feeding research with both species are reviewed and research needs to support their commercial production in the region are discussed.     

Effect of Density at Harvest on the Growth Performance and Profitability of Hatchery‐reared Spotted Rose Snapper,Lutjanus guttatus,Cultured in Floating Net Cages

This study evaluated the effect of the density at harvest on the performance and profitability of hatchery‐reared spotted rose snapper cultured in cages. The fish were stocked at harvest densities of 15, 20, and 22 kg/m³ in cages of 222 and 286 m³. More than 39,000 snapper fingerlings with an initial weight of 14 g were stocked. The fish were fed an extruded diet and cultured over a 360 d period. The thermal growth coefficient ranged from 0.04 to 0.05 and survival was 95% for all treatments, with the highest final weight (436.8 g) observed for fish reared at a density of 20 kg/m³. The allometric value b indicated that hatchery‐raised, cage‐cultured snapper were heavier than their wild counterparts. The major costs were feed (ranging from 44.7–45.9%), labor (22.4–32.6%), and seed costs (20.2–26.1%). The total production cost ranged from US$ 6.5 to US$ 7.5/kg. The baseline scenario was not economically feasible. However, a 10% increase in the sales price resulted in increases in the internal rate of return (183%) and net present value (US$ 97,628.9). These results suggest that L. guttatus has the potential for commercial production in cages.     

Evaluation of apparent digestibility coefficients of individual feed ingredients in spotted rose snapper Lutjanus guttatus (Steindachner, 1869)

Apparent digestibility coefficients (ADCs) for dry matter, crude protein, energy and essential amino acids for five commonly used feed ingredients were determined for juvenile spotted rose snapper Lutjanus guttatus (average body weight 90.6 g). ADCs were determined using the stripping technique to collect faeces after fish were fed a reference diet and test diets composed of 700 g kg^?1 reference diet and 300 g kg^?1 test ingredient. Chromic oxide (Cr₂O₃) was used as an inert indicator. Ingredients tested included sardine fishmeal (FM), canola meal (CM), tuna by‐products meal (TBM), poultry by‐product meal pet grade (PBM‐PG) and solvent‐extracted soybean meal (SBM). In general, all ingredients showed high digestibility values for all essential amino acids, although differences were detected among ingredients. ADC values for dry matter, protein and energy ranged 77.0–80.4%, 84.3–82.5% and 89–88.8%, respectively, for marine ingredient and land‐based animal protein sources, and 75.0–74.2%, 81.5–80.9% and 87.4–86.8%, respectively, for the plant‐based protein source. SBM, TBM and PBM‐PG should be further evaluated in feeding trials as partial FM replacements in rose snapper L. guttatus diets. Knowledge of ADC values for these ingredients will allow feed producers to develop nutritionally balanced, low‐cost feed formulations for this species.     

Development of digestive enzyme activity in spotted rose snapper,Lutjanus guttatus (Steindachner, 1869) larvae

We describe digestive enzyme activity during the larval development of spotted rose snapper, Lutjanus guttatus. Trypsin, chymotrypsin, leucine aminopeptidase, pepsin, amylase, lipase, and acid and alkaline phosphatase activities were evaluated using spectrophotometric techniques from hatching through 30 days. The spotted rose snapper larvae present the same pattern of digestive enzyme activity previously reported for other species in which pancreatic (i.e., trypsin, chymotrypsin, amylase, and lipase) and intestinal (i.e., acid and alkaline phosphatases and leucine aminopeptidase) enzymatic activities are present from hatching allowing the larvae to digest and absorb nutrients in the yolk-sac and live prey by the time of first feeding. The digestive and absorption capacity of the spotted rose snapper increases during the larval development. A significant increase in individual activity of all enzymes occurs at 20 DAH, and around 25 DAH, the juvenile-type of digestion is observed with the appearance of pepsin secreted by the stomach, suggesting that maturation of the digestive function occurs around 20–25 DAH. Our results are in agreement with a previous suggestion that early weaning may be possible from 20 DAH. However, the patterns of enzymatic activities reported in our study should be considered during the formulation of an artificial diet for early weaning of the spotted rose snapper.     

GnRHa‐induced Multiple Spawns and Volition Spawning of Captive Spotted Rose Snapper,Lutjanus guttatus,at Mazatlan,Mexico

Sexual maturation and induced spawning treatments were carried out with captive spotted rose snapper, Lutjanus guttatus. A total of 3013 × 10⁶ eggs (64.7% were floating) were produced from eight treated females in 42 spawns induced with GnRHa implants during the course of the present study. GnRHa ethylene‐vinyl acetate copolymer effective doses were 204 ± 11 µg/kg in June 2005, and 224 ± 13 µg/kg in July 2005. General fertilization was 50.9 ± 34.5% and 12–14 h after spawning, viability of floating eggs was 90.4 ± 12.4%. Mean incubation period at 29–31 C was 18–20 h, and mean hatching was 94.4 ± 8.2% (73–100%). Newly hatched larvae were 2.18 ± 0.15 mm in total length (TL). One month after the last hormone experiment, previously GnRHa‐treated and untreated fish began spawning voluntarily. Hormone‐treated breeders had higher fecundity than untreated fish, producing 72.5 million eggs versus 13.9 million eggs for the untreated fish, over the following 11 mo. Combined data of volitional spawning for total egg fertilization, viability, hatching, and larval TL were 77.7 ± 1.8%, 90.3 ± 1.3%, 87.9 ± 2%, and 2.50 ± 0.12 mm, respectively. These results can ensure the sustainability of a commercial hatchery.     

In vitro protein digestibility of different grow‐out stages of spotted rose snapper (Lutjanus guttatus,Steindachner, 1869)

The aim of this study was to compare in vitro protein digestibility between two groups of fish, at early (21 g) and late stages (400 g) of spotted rose snapper Lutjanus guttatus, to evaluate the degree of hydrolysis (DH) and total amino acid release (TAAR) using crude extracts from stomach, pyloric caeca and intestine of 13 protein ingredients including marine, animal and plant meals. Degree of hydrolysis and TAAR were measured by a pH‐Stat method, and the PAGE‐Zymogram was also used as complementary technique. Differences in DH were found between both grow‐out stages mainly in the alkaline hydrolysis phase. Fish and squid meals (marine sources) had the highest DH and TAAR, followed by porcine meat and poultry meal by‐products from recycling sources, and soybean and canola meals (plant sources), which represent better protein sources for use in practical diets. Stomach zymograms showed two pepsin isoforms in both grow‐out stages. Pyloric caeca and intestine zymograms showed five bands with proteolytic activity in the early grow‐out stage, whereas four additional bands were found in late grow‐out stage. Alkaline proteases were identified as serine and metalloproteases. Thus, L. guttatus presents an ontogenetically differentiated digestive enzyme pattern that modifies the DH and TAAR of different protein sources.     

The Scale‐up of Spotted Rose Snapper,Lutjanus guttatus,Larval Rearing at Mazatlan,Mexico

The scale‐up of spotted rose snapper, Lutjanus guttatus, larval rearing is described. Fertilized eggs (480,000) were obtained from a 1‐d harvest of a natural spawning captive broodstock acclimatized for 1 yr and 6 mo in two fiberglass tanks (18 m³). Fourteen hours after spawning, 89.6% of the collected eggs were floating, of which 96.2% were transparent with live embryos. Incubation at 25–26 C lasted 21 h, with 90.2 ± 2.1% hatching percentage of normal larvae. The percentage of viable larvae at 48 h after hatching was 79.7 ± 1.9%. Initial stocking density was 10.4 ± 1.0 larvae/L 2 days after hatching (d.p.h.). A total of 22,600 juveniles (1256 ± 170 juveniles/m³) were harvested from six 3‐m³ cylindrical fiberglass tanks. Average survival was 12.1 ± 1.1%. Final mean length and weight were 5.5 ± 0.05 cm and 2.24 ± 0.04 g, respectively. Growth expressed in total length was TL = 2.1476e^0.0543t (R² = 0.9911). Final mean biomass and condition factor were 2.8 kg/m³, 12.3% and 1.346. General length‐weight ratio was W = 0.05460 LT^2.2306.     

Outbreak of hirame rhabdovirus infection in cultured spotted sea bass Lateolabrax maculatus on the western coast of Korea

In this study, we determined the cause of a disease outbreak in spotted sea bass, Lateolabrax maculatus reared in culture cages on the western coast of Korea in 2013. The major signs in the diseased fish exhibited were haemorrhaging on the membranes of the abdomen, gastrointestinal organs and opercular gills, as well as an enlarged spleen. No external morphological signs of infection were visible, except for a darkening in colour. No parasites or pathological bacteria were isolated from the diseased fish; however, epithelioma papulosum cyprini (EPC) cells inoculated with tissue homogenates from the diseased fish showed cytopathic effects (CPEs). Virus particles in the EPC cells were bullet‐shaped, 185–225 nm long and 70–80 nm wide, characteristic of Rhabdoviridae. Polymerase chain reaction analyses of homogenized tissues from the diseased fish and supernatants of cell cultures with CPEs indicated specific, 553‐bp‐long fragments corresponding to the matrix protein gene of the hirame rhabdovirus (HIRRV). Phylogenetically, the HIRRV phosphoprotein gene of spotted sea bass was more closely related to phosphoproteins from Chinese and Polish HIRRV strains than from other Korean strains. To our knowledge, this is the first report of HIRRV infection in cultured spotted sea bass.     

Effect of the dusk photoperiod change from light to dark on the incubation period of eggs of the spotted rose snapper, Lutjanus guttatus (Steindachner)

Spotted rose snapper, Lutjanus guttatus (Steindachner), eggs were incubated under different photoperiods to examine the effect of photoperiod on incubation. The eggs from two fish were incubated under five artificial photoperiods: constant dark (D), constant light (L) from 06:00 hours and 6, 10 and 14 h of light from 06:00 hours. The eggs from seven other fish were incubated under a natural photoperiod. Different spawning times (21:00 – 01:00 hours) and different photoperiods combined to give the start of the dusk photoperiod change after 11–23 h of incubation. Constant light or applying the dusk photoperiod change after ≥20 h of incubation appeared to extend the hatching period. The mean hatching period for groups of eggs incubated in darkness or that received the dusk photoperiod change after ≤19 h of incubation (n=8 different groups) was 2 h 15±10 min, which was significantly lower (P<0.05) than the mean hatching period of 4 h±37 min for groups that did not receive the dusk photoperiod change or that received the dusk photoperiod change after ≥20 h of incubation (n=9 groups). However, despite these differences, the majority of the eggs hatched during a 2–3 h period from 17 to 20 h of incubation, and a sigmoid regression (r²=0.9) explained the relationship between percentage hatch and hours of incubation for all photoperiod groups.     

Ascorbic acid requirement and histopathological changes due to its deficiency in juvenile spotted rose snapper Lutjanus guttatus (Steindachner, 1869)

A 13-week feeding trial was conducted to determine the optimal dietary ascorbic acid (AA) requirement of juvenile spotted rose snapper (Lutjanus guttatus). Six experimental diets containing 0, 7, 19, 29, 62 and 250 mg AA equivalent kg^?1 diet, supplied as l-ascorbyl-2-polyphosphate designated as VC0, VC7, VC19, VC29, VC62 and VC250, were fed ad libitum to triplicate groups of 20 juveniles [initial weight (IW) of 8 ± 1.85 g]. Nutrient deficiency resulting in fin erosion, dark skin, desquamation and erratic swimming was observed after 8 weeks in fish fed diets from 0 to 29 mg AA kg^?1. Fish that were fed all diets showed gill, kidney and brain alterations. The degree of tissue change values indicates that increasing vitamin C (VC) levels reduces these alterations. Fish fed diets VC29, VC62 and VC 250 showed a significantly higher growth rate in comparison with those fed the diets VC0, VC7 and VC17 (P > 0.05). The dietary requirement of VC in L. guttatus was estimated to be 29 mg kg^?1 of AA based on weight gain and specific growth rate, but more than 250 mg kg^?1 of AA is required to eliminate clinical signs and histopathological lesions.     

Vitrification of sperm from marine fish: effect on motility and membrane integrity

Our goal was to develop a standardized approach for sperm vitrification of marine fish that can be applied generally in aquatic species. The objectives were to: (i) estimate acute toxicity of cryoprotectants over a range of concentrations; (ii) evaluate the properties of vitrification solutions (VS); (iii) evaluate different thawing solutions and (iv) evaluate sperm quality after thawing by examination of motility and membrane integrity. Sperm were collected from red snapper (Lutjanus campechanus), spotted seatrout (Cynoscion nebulosus) and red drum (Sciaenops ocellatus). A total of 29 combinations of cryoprotectants were evaluated for toxicity and glass formation. Samples were loaded onto 10‐μL polystyrene loops and plunged into liquid nitrogen. There was a significant difference (P < 0.05) in post‐thaw motility among VS and among species when using the same VS. The sperm in VS of 15% DMSO + 15% ethylene glycol + 10% glycerol + 1% X‐1000^? + 1% Z‐1000^? had an average post‐thaw motility of 58% and membrane integrity of 19% for spotted seatrout, 38% and 9% for red snapper, and 30% and 19% for red drum. Adaptations by marine fish to higher osmotic pressures could explain the survival in the high cryoprotectant concentrations. Vitrification offers an alternative to conventional cryopreservation.     

Reproductive performance in induced and spontaneous spawning of the mangrove red snapper, Lutjanus argentimaculatus: a potential candidate species for sustainable aquaculture

A reliable breeding technique was developed for the mangrove red snapper, Lutjanus argentimaculatus (Forsskal 1775), to help sustain the aquaculture of this immensely popular species in Southeast Asia. Using standardized indices of female maturity (based on mean oocyte diameter of ≥0.40 mm), time of injection (1000–1130) and sex ratio (one female to two males), a single injection of 100 μg kg^?1 luteinizing hormone‐releasing hormone analogue (LHRHa) (n=16 fish), but not 50 μg kg^?1 (n=five fish), successfully induced egg (62.5% success rate) and larval (43.8%) production. Human chorionic gonadotropin (hCG) at 500 IU kg^?1 (n=five fish) also failed to induce spawning, but doses of 1000 (n=22 fish) and 1500 IU kg^?1 (n=15 fish) gave spawning (77.3% and 80.0% respectively) and hatching success rates (72.7% and 60.0% respectively) that were not significantly different from those of 100 μg kg^?1 LHRHa. No spawning was observed in saline‐injected controls (n=seven fish). While mean spawning latency, egg diameter, egg production per spawn, percent egg viability, hatching rate, percent of normal larvae and cumulative survival of eggs to normal larvae did not differ significantly among the effective hormones and doses, 1000 IU kg^?1 hCG had a higher percentage (76.5%) of total spawns with egg production per spawn in excess of one million than those of 1500 IU kg^?1 hCG (50.0%) and 100 μg kg^?1 LHRHa (40.0%). Mangrove red snapper spontaneously spawned from March–April to November–December with a peak of egg collection and spawning in May–June. Egg collection per spawn ranged from 0.05 to 6.35 million. Spontaneous spawning of mangrove red snapper exhibited lunar periodicity with spawns mostly occurring 3 days before or after the last quarter and new moon phases and occurred consistently between 02:00 and 04:00 hours. High fecundity and good egg quality, coupled with the ability to respond to induce spawning or natural spawning in captivity, provide a sound basis for improving the sustainability of red snapper aquaculture in Southeast Asia.     

Investigation of the nutritional requirements of Australian snapper Pagrus auratus (Bloch & Schneider 1801): digestibility of gelatinized wheat starch and clearance of an intra-peritoneal injection of d-glucose

Two experiments were performed to investigate the digestibility and utilization of carbohydrate sources by Australian snapper Pagrus auratus. In the first experiment, snapper of two different size classes (110 and 375 g) were fed a reference diet containing no starch (REF) or diets containing 150 (PN15), 250 (PN25), 350 (PN35) or 450 g kg^?1 (PN45) of 100% gelatinized wheat starch to investigate the interactive effects of fish size and starch inclusion level on apparent organic matter (OM) or gross energy (GE) digestibility (ADC), post‐prandial plasma glucose concentration, hepatosomatic index (HSI) and liver or tissue glycogen content. A second experiment used a 72 h time course study to investigate the ability of larger snapper (300–481 g) to clear an intra‐peritoneal injection of 1 g d ‐glucose kg^?1 body weight (BW). Organic matter and GE ADCs declined significantly in both fish sizes as the level of starch increased (PN45energy small fishenergy large fish). There was no interaction between fish size and inclusion level with respect to GE or OM ADCs. Gross energy ADC for both sized fish was described by the linear function GE ADC=104.97 (±3.39)–0.109 (±0.010) × inclusion level (R²=0.86). Hepatosomatic index, liver and muscle glycogen concentrations were significantly elevated in both small and large snapper‐fed diets containing gelatinized starch compared with snapper fed the REF diet. Three‐hour post‐prandial plasma glucose concentrations were not significantly affected by fish size, inclusion level or the interaction of these factors (REF=PN15=PN25=PN35=PN45), and ranged between 1.60 and 2.5 mM. The mean±SD resting level of plasma glucose (0 h) was 2.4±1.1 mM. Circulating levels of plasma glucose in snapper peaked at 18.9 mM approximately 3 h after intra‐peritoneal injection and fish exhibited hyperglycaemia for at least 12–18 h. There were no significant differences between the plasma glucose concentrations of snapper sampled 0, 18, 24, 48 or 72 h after injection (0=18=24=48=72<12< 1<3=6 h), indicating snapper required almost 18 h to regulate their circulating levels of glucose to near‐basal concentrations. Australian snapper are capable of digesting moderate levels of gelatinized wheat starch; however, increasing the dietary content of starch resulted in a reduction in OM and GE digestibility. Smaller snapper appear to be less capable of digesting gelatinized starch than larger fish, and levels above 250 and 350 g kg^?1 of diet are not recommended for small and large fish respectively. Snapper subjected to an intra‐peritoneal injection of d ‐glucose have prolonged hyperglycaemia; however, the post‐prandial response to the uptake of glucose from normally digested gelatinized starch appears to be more regulated.     

Brook charr, Salvelinus fontinalis (Mitchill), and cryptobiosis: a potential salmonid reservoir host for Cryptobia salmositica Katz, 1951

Abstract. Laboratory-raised Cryptobia -susceptible brook charr, Salvelinus fontinalis (Mitchill), and rainbow trout, Oncorhynchus mykiss (Walbaum), were vaccinated intraperitoneally with a live Cryptobia salmositica vaccine (250000 parasites per fish), and 4 weeks later were challenged with the pathogen (250000 parasites per fish). Unvaccinated and infected brook charr had high parasitaemias but no clinical signs of disease, while unvaccinated and infected rainbow trout had anaemia and general oedema. Vaccinated and challenged fish had very low parasitaemias compared to unvaccinated and infected brook charr and rainbow trout. Complement fixing antibodies were detected in vaccinated and challenged fish 2 weeks after challenge. Unvaccinated and infected brook charr had consistently higher litres of complement fixing antibody than unvaccinated and infected rainbow trout. Parasitaemias were lower in all fish in which titres of complement fixing antibody were high. In a second experiment, brook charr inoculated intraperitoneally or intramuscularly with 100000 C. salmositica per fish had high parasitaemias but no anaemia or other clinical signs. The results show that susceptible brook charr do not suffer from cryptobiosis and may serve as reservoir hosts for C. salmositica in areas where the disease is prevalent. Vaccination to reduce the parasitaemia when fish become infected may be a control strategy in these areas.     

Effects of the gill monogenean Zeuxapta seriolae (Meserve, 1938) and treatment with hydrogen peroxide on pathophysiology of kingfish, Seriola lalandi Valenciennes, 1833

Infections by the gill fluke Zeuxapta seriolae are a serious concern for sea cage aquaculture of kingfish, Seriola lalandi. The present study aimed to determine the pathophysiological effects of a progressive infection with Z. seriolae and the effects of treatment with hydrogen peroxide. For the progression of infection study, infected fish were taken from a sea cage farm, treated to remove parasites and then infected by cohabitation with heavily infected fish. Samples were taken at 2-week intervals for 8 weeks. Infection intensity peaked at 4 weeks post-infection (mean intensity 565.9) and the number of mature worms (2 mm fixed length or larger) peaked at 6 weeks post-infection. Attachment of Z. seriolae appeared to cause little localized pathology; however, the occurrence of hyperplastic lamellae increased as the infection progressed. Haemoglobin concentrations were negatively correlated with Z. seriolae intensity and were lower than controls at 4 weeks (35.8% decrease) and 6 weeks (57.4% decrease) post-infection. Blood lactate concentration and plasma osmolality increased throughout the course of infection. For the effect of treatment experiment, groups of infected and non-infected fish were sampled either before or after treatment with hydrogen peroxide. Treated fish from both infected and uninfected groups had increased plasma lactate, osmolality and pH compared with pre-treatment groups. Treatment with hydrogen peroxide appeared to have acute effects on fish health but the magnitude (e.g. lactate, osmolality) and extent of the effects (e.g. haemoglobin) was much less than that caused by chronic infection with Z. seriolae.     

Surviving the effects of barotrauma: assessing treatment options and a ‘natural’ remedy to enhance the release survival of line caught pink snapper (Pagrus auratus)

A new technique to ameliorate the effects of barotrauma was tested based on observations of pink snapper, Pagrus auratus (Forster), inadvertently piercing their everted stomach with their teeth and releasing trapped swim bladder gases. This technique was termed buccal venting and involved piercing the everted stomach protruding into the buccal cavity or out of the mouth with a 16‐gauge hypodermic needle (a practice previously not encouraged). Short‐term (~3 days) survival of buccal‐vented fish was not significantly different from laterally vented fish nor untreated controls. Both buccal and lateral venting techniques were shown to cause no harm and allowed fish to return to depth. The short‐term (1–3 days) post‐release survival of line caught snapper was 88% with no significant difference in survival across three depth ranges tested (37–50, 51–100 and 101–180 m). Survival of sublegal pink snapper (<35 cm TL) was not significantly different (P > 0.05) from that of legal‐sized fish (≥35 cm TL). Healing of the swim bladder was observed in 27% of pink snapper dissected after ≤3 days in captivity, and healing of stomachs was observed in 64% of pink snapper that had been buccal vented. Relatively high post‐release survival rates of line caught pink snapper may offer some protection for snapper stocks where high fishing pressure and legal size restrictions result in the majority of the catch having to be released.     

Zebrafish (Danio rerio) as an animal model for bath infection by Flavobacterium psychrophilum

Flavobacterium psychrophilum is the causative agent of bacterial cold-water disease and rainbow trout syndrome in freshwater salmonid fish worldwide, generating injuries and high mortality rates. Despite several studies on this bacterium, the infection mechanism remains unknown due to limitations in the employed animal models. In this work, we propose using zebrafish (Danio rerio) as a model for studying bacterial pathogenicity. To substantiate this proposal, zebrafish infection by F. psychrophilum strain JIP 02/86 was characterized. Zebrafish larvae were infected using the bath method, and morphological changes and innate immune system activation were monitored using transgenic fish. Salmonid-like infection phenotypes were observed in 4.74% of treated larvae, as manifested by fin, muscle and caudal peduncle damage. Symptomatic and dead larvae accounted for 1.35% of all challenged larvae. Interestingly, infected larvae with no infection phenotypes showed stronger innate immune system activation than specimens with phenotypes. A failure of function assay for myeloid factor pu.1 resulted in more infected larvae (up to 43.5%), suggesting that low infection rates by F. psychrophilum would be due to the protective actions of the innate immune system against this bacterium in zebrafish larvae. Our results support the use of zebrafish as an infection model for studying F. psychrophilum. Furthermore, the percentage of infected fish can be modulated by disturbing, to varying extents, the differentiation of myeloid cells. Using this evidence as a starting point, different aspects of the infection mechanism of F. psychrophilum could be studied in vivo.