Completion of the Pacific bluefin tuna Thunnus orientalis (Temminck et Schlegel) life cycle

Tuna aquaculture is currently dependent on the wild capture of juveniles for production. The development of hatchery technology for bluefin and other tunas would be a major step forward in improving sustainability of their aquaculture. The present study overviews the technology in the life cycle completion of the Pacific bluefin tuna (PBT) Thunnus orientalis (Temminck et Schlegel) under aquaculture conditions in Kinki University, and the problems to be solved for the establishment of tuna hatchery technology. On 23 June 2002, broodstock of PBT that were artificially hatched and reared spontaneously spawned in captivity. The resulting eggs hatched and were subsequently reared to the juvenile stage. The spawning fish were the result of a research project started in 1987 to rear wild‐caught juvenile PBT that were several months old. Fertilized eggs were obtained from these fish in 1995 and 1996. Resulting juveniles (the artificially hatched first generation) were reared to maturity and spawned in 2002. Over the summer of 2002, 1.63 million eggs from these fish were used for a mass rearing experiment, and 17 307 juveniles were produced and transferred to an open sea net cage. Of these artificially hatched second‐generation PBT, 1100 grew to approximately 95 cm total length and 14 kg body weight in 22 months. This procedure means the completion of PBT life cycle under aquaculture conditions, which was first attained among large tuna species. The problems awaiting solution in PBT hatchery production are their unpredictable spawning in captivity, to improve survival during the first 10 days post hatch, to reduce cannibalism in larval and juvenile stages, and to solve collision problem causing high mortality during the juvenile stage.     

Infectious pancreatic necrosis virus in fish by‐products is inactivated with inorganic acid (pH 1) and base (pH 12)

The aquaculture industry needs a simple, inexpensive and safe method for the treatment of fish waste without heat. Microbial inactivation by inorganic acid (HCl) or base (KOH) was determined using infectious pancreatic necrosis virus (IPNV) as a model organism for fish pathogens. Salmonella and spores of Clostridium perfringens were general hygiene indicators in supplementary examinations. IPNV, which is considered to be among the most chemical‐ and heat‐resistant fish pathogens, was reduced by more than 3 log in 4 h at pH 1.0 and pH 12.0. Salmonella was rapidly inactivated by the same treatment, whereas spores of C. perfringens were hardly affected. The results indicate that low and high pH treatment could be particularly suitable for fish waste destined for biogas production. pH treatment at aquaculture production sites could reduce the spread of fish pathogens during storage and transportation without disturbing the anaerobic digestion process. The treatment could also be an alternative to the current energy‐intensive steam pressure sterilization of fish waste to be used by the bioenergy, fertilizer and soil improver industries.     

Comparison of iodine and glutaraldehyde as surface disinfectants for red porgy (Pagrus pagrus) and white sea bream (Diplodus sargus sargus) eggs

The efficacy of iodine and glutaraldehyde as fish egg surface disinfectants were assessed in red porgy (Pagrus pagrus) and white sea bream (Diplodus sargus sargus) eggs, two species of interest for Mediterranean aquaculture. Iodine was effective in reducing the bacterial load of the 1-day-old eggs when applied at 50 mg L⁻¹ for 5 min. The same concentration did not cause any significant change in hatching success or survival of the larvae for the first 5 days. Glutaraldehyde failed to reduce the bacterial load of the fish eggs at concentrations that were safe for the eggs (100 mg L⁻¹ for 5 min), as it had a significant effect in preventing hatching of the developed embryo. Disinfecting 0-day-old eggs with iodine resulted in a significant reduction of hatching percentage, while larval survival thereafter was unaffected. The results of the present study suggest that iodine may be an appropriate egg disinfectant for both red porgy and white sea bream.     

Strain-specific vital rates in four Acartia tonsa cultures, I: Strain origin, genetic differentiation and egg survivorship

Successful development of planktonic copepods for use as live feed in marine aquaculture relies on optimization of environmental conditions for population growth and egg storage. This study examined strain-specific differences in egg survivorship during cold-storage-induced quiescence in four cultures of the widespread marine calanoid Acartia tonsa Dana, 1849. Experimental cultures were obtained from Øresund, Denmark (DIFRES), Kiel, Germany (KIEL), Turkey Point, Florida, USA (FL), and Mobile Bay, Alabama, USA (AL), and were shown to derive from three highly distinct mitochondrial clades. Eggs from Gulf of Mexico strains had low tolerance for cold storage, and showed very low hatching success after 10 days. In contrast, Baltic Sea strains produced eggs able to tolerate up to 150 days of cold storage, with the DIFRES strain showing the highest egg survivorship during the experiment. Eggs from the Kiel strain showed an increase in hatching over time, indicating the presence of dormant eggs. Parental rearing temperature was also found to affect egg survivorship during quiescence in the DIFRES strain, with lower hatching success observed among eggs produced at 25 °C than at 17 °C. The DIFRES strain is recommended as the optimal strain for use in aquaculture, and conditions for cold storage of eggs are discussed.     

The settlement and reproductive success of Lepeophtheirus salmonis (Krøyer 1837; Copepoda: Caligidae) on atypical hosts

The reproductive success of Lepeophtheirus salmonis settled on host and non‐host fish has been compared. Triplicate single species tanks of Atlantic salmon, marine three‐spined sticklebacks, saithe and Atlantic cod were exposed to 10 adult female L. salmonis per tank (n=30 lice per species). Adult female L. salmonis settlement and egg string production occurred only on salmon and cod, with no egg production occurring on saithe and three‐spined sticklebacks. The number of eggs in egg strings, hatching success of eggs and the survival of all larval stages to the copepodid stage were severely affected by the species of fish on which female L. salmonis had settled. L. salmonis settled on cod produced significantly fewer eggs, lower hatching rates and lower survival rates of larvae than females on Atlantic salmon. The production of egg strings by L. salmonis females infecting cod, which successfully hatch and moult through to the infective copepodid stage, albeit in small numbers, is discussed in terms of the implications to aquaculture and salmon and cod farming scenarios.     

Biochemical and technical observations supporting the use of copepods as live feed organisms in marine larviculture

The use of live prey is still necessary for a large number of raised fish species. Small sized rotifers are usually used as live preys during the first days of feeding in small mouth fish. An alternative to this is the use of copepods as prey for first feeding. In this study, the sizes, weight and biochemical contents of two copepods and one rotifer species raised on similar algal food conditions were compared. Rotifers contained a higher proportion of essential amino acids in the free amino acid (FAA) fraction (43%) than copepods (30–32%). However, rotifers had lower levels of important fatty acids like DHA (7% compared with 23–32% in copepods) and their DHA/EPA ratio was lower than that in copepods (0.54 compared with 1.35–1.63 in copepods). The FAA pattern of the preys tended to be species‐specific and its implications from an aquaculture point of view is discussed. In contrast, the‐protein bound amino acids tended to be very conservative among the studied organisms. The second part of the work is focused on ‘the price’ of hatching in Acartia tonsa eggs before or after cold storage at 3°C. The fatty acid contents in A. tonsa tended to decrease with the storage time. It also decreased with hatching of the nauplii, but its proportion compared with the dry weight remained constant.     

Identification of conditions underlying production of geosmin and 2-methylisoborneol in a recirculating system

Geosmin and 2-methylisoborneol (MIB) are semi-volatile terpenoid compounds produced as secondary metabolites by benthic and planktonic cyanobacteria, several genera of fungi, and various actinomycetes. These off-flavor compounds pose a heavy economic burden in the aquaculture industry rendering fish unmarketable unless purified by purging with large quantities of clean water. In the present study, the presence of off-flavor compounds was examined in a recirculating aquaculture system (RAS) for tilapia culture. In this zero-discharge system, where water from the fish basins is recirculated through parallel aerobic (drum filter and a trickling filter) and anaerobic treatment loops (sedimentation/digestion basin), concentrations of geosmin and, in particular, MIB were highest in the aerobic treatment loop. Lowest concentrations were detected in the anaerobic treatment loop. This latter finding pointed toward a possible reduction of these compounds in this basin. Two bacterial strains of the streptomycetes family were isolated from the aerobic, organic-rich, drum filter and the nitrifying trickling filter. In vitro tests with these isolates, closely related to Streptomyces roseoflavus and Streptomyces thermocarboxydus, revealed that MIB production exceeded geosmin production under all conditions tested and was significantly higher under aerobic than under anoxic conditions. Under the latter conditions, with nitrate as an electron donor, the S. roseoflavus-like isolate was capable of denitrification. Based on the results obtained in this study, it was concluded that aerobic, organic-rich conditions stimulate the growth of actinomycetes and subsequent production of geosmin and MIB in the system. The observed reduction of these compounds in the anaerobic water treatment component may serve in designing treatment steps aimed at alleviating the problem of geosmin and MIB accumulation in recirculating systems.     

Are Acartia tonsa cold‐stored eggs a suitable food source for the marine ornamental species Amphiprion polymnus? A feeding study

Copepods are the natural food items for marine fish larvae but are still difficult to be cultured on a continuous basis. Therefore, suitable storage techniques for copepod subitaneous eggs are of great interest. Cold‐stored copepod embryos still develop and retain a physiological activity during the cold storage period. As a consequence, their nutritional quality may change over the time of storage with these changes possibly affecting both eggs viability and larval fish survival and development. In this study, the clownfish, Amphiprion polymnus, was used as an experimental model to compare, for the first time, the effects of diets based on enriched rotifers and Artemia (control), Acartia tonsa copepods of a continuous culture and A. tonsa originated from 6 months cold‐stored eggs. The effects of the different diets were tested through morphometric, molecular and biochemical approach. This study demonstrated that after a 6 months cold storage period, the quality of copepods obtained from those eggs was suboptimal for A. polymnus larval rearing. In fact, larvae fed those copepods showed lower growth and survival performances respect to the other experimental groups.     

Calcium alginate capsules for oral administration of fish probiotic bacteria: assessment of optimal conditions for encapsulation

The application of probiotics in aquaculture represents a promising alternative for disease prevention. These microorganisms must survive adverse conditions during handling and storage to be administered in high concentrations to the host. This is especially important when stressful conditions, such as low water contents, are present in animal feed. Bacterial encapsulation has been used to maintain probiotic viability in human food; however, the usefulness of the encapsulation techniques in animal feed needs to be evaluated. In the present study, optimal conditions for encapsulation in alginate of a fish probiotic Shewanella putrefaciens strain (Pdp11) have been determined. Different alginate (1%, 2%, 3% and 4% w/v) and calcium chloride (0.5%, 1% 2% and 3% w/v)concentrations were used to elaborate alginate beads. The results obtained indicate that S. putrefaciens Pdp11 can be encapsulated successfully in calcium alginate beads. The percentages of encapsulated cells were above 80%, the lowest efficiency rates corresponding to high calcium availability (3%). In addition, capsules containing viable S. putrefaciens Pdp11 can be stored at 4 °C for at least 1 month, survival rates being above 90%. On the contrary, storage of the capsules at 22 °C resulted in 40% viability loss within 30 days. Finally, the survival of encapsulated probiotics through fish gastrointestinal tract has been demonstrated.     

Effects of Thyroxin and Domperidone on Oocyte Maturation and Spawning Performances in the Rabbit Fish,Siganus guttatus

Thyroxin (T₄) is proven to have various functions in fish reproduction. In this study, we investigated oocyte maturation and spawning performance in the rabbit fish, Siganus guttatus, orally exposed to different doses of T₄ (0.05, 0.25, and 0.5 mg/kg fish) during vitellogenesis. No statistically significant differences of reproductive characteristics were observed among the treatments. However, the group that was exposed to the dose of 0.5 mg/kg spawned after receiving a hormone injection. The findings suggest that feeding T₄ during vitellogenesis did not advance oocyte maturation, but probably could induce spawning in rabbit fish. In a separate experiment, we investigated the effects of orally administered domperidone (DOM) on reproductive performances of the female rabbit fish. The study showed that oral administration of DOM during the early stages of the reproductive cycle had no significant effects on oocyte maturation and spawning performance. Overall, these findings suggest that DOM may not be needed for the induction of maturation and spawning of this species under aquaculture conditions. These practical investigations were conducted with a view to attempt reducing drug use, production costs, and support sustainable aquaculture.     

Impact of bacteria on short-term storage of salmonid eggs

Unfertilized eggs of steelhead, Oncorhynchus mykiss (Walbaum 1792), were stored at a low temperature (～0°C) with antibiotics (penicillin and streptomycin) for up to 22 days and fertility assessed. Unfertilized eggs of chinook salmon, Oncorhynchus tshawytscha (Walbaum 1792), were stored at a low temperature (～0°C) either with or without antibiotics for up to 24 days and fertility assessed. There were no significant decreases in fertility under these conditions. Steelhead eggs were maintained at 4°C for up to 15 days with or without added bacteria and with or without gentamicin. Gentamicin inhibited bacterial growth during storage at 4°C and its use resulted in a less pronounced decline in fertility with storage. These results suggest that low temperatures and antibiotics play an important role in extending the period over which salmonid eggs can be successfully stored.     

The Use of Dairy Protocols for Sperm Cryopreservation of Blue Catfish Ictalurus furcatus

The commercial‐scale production of fish by use of artificial (induced) spawning would require reliable, large‐volume sources of sperm. Cryopreservation can be used to preserve and store sperm within commercial and research germplasm repositories, but is limited in its application to aquaculture. Straw volume and cooling chamber size restrict the quantity of sperm that can be frozen, and straws must be filled by hand. In contrast, the dairy industry has refined methods for freezing of bull sperm, including automation of straw filling and the use of large cooling chambers. These methods could be used for commercial‐scale cryopreservation of fish sperm, although application would require testing. To supply sperm in large volumes, bags originally developed for swine semen could be cooled using dairy protocols and used as a container for fish sperm. The current study documented the use of commercial‐scale dairy cryopreservation techniques for the production of hybrids of channel catfish Ictalurus punctatus (female) by blue catfish Ictalurus furcarus. Four cryoprotectants (methanol, dimethyl sulfoxide, dimethyl acetamide, and glycerol) were initially evaluated for use with blue catfish sperm. During May 2000 and March to April 2001, suspensions of blue catfish sperm were cryopreserved with 10% methanol in 0.5‐mL French straws and in commercial swine semen bags (Cochette^* bags, IMV International. Minneapolis, Minnesota, USA). Cryopreservation took place at a dairy breeding cooperative, using technology employed for bull semen. Sperm motility before freezing was 26 ± 18% during Year 1 (2000) and 62 ± 30% during 2001. Sperm were thawed at 40 C and used to fertilize the eggs of channel catfish (yielding hybrids). Motility after thawing for sperm frozen in 0.5‐mL straws was 11 ± 10% during 2000 and 50 ± 24% during 2001. Motility after thawing was 41 ± 17% for sperm frozen in swine semen bags in 5‐mL aliquots and 43 ± 10% for sperm frozen in 10‐mL aliquots. Neurulation of eggs fertilized with thawed sperm from straws was 83 ± 13% during 2000 and 54 ± 27% during 2001. Neurulation was 57 ± 24% using sperm frozen in swine semen bags in 5‐mL aliquots and 55 ± 10% using sperm frozen in 10‐mL aliquots. There was no correlation between sperm motility before freezing (in 0.5‐mL straws) and after thawing during 2000 (r= 0.52) or during 2001 (r= 0.49). In addition, there was no correlation between initial motility and neurulation of channel catfish eggs fertilized using thawed sperm during 2000 (r= 0.14) or during 2001 (r= 0.29). Sperm of blue catfish can thus be cryopreserved at a commercial scale using dairy protocols and can be made available for the production of hybrid catfish when viable eggs are available.     

An automated recirculation aquaculture system based on fuzzy logic control for aquaculture production of tilapia (<Emphasis Type="Italic">Oreochromis niloticus</Emphasis>)

The development of an automated recirculation aquaculture system (ARAS) is presented here. The production system facility was built in a 672-m² polyethylene greenhouse using four 20-m³ tanks, each of which was stocked with 1,000 tilapia (O. niloticus). The growth of the fish was evaluated from a starting weight of 2 g to a final average weight of 418 g, during a production cycle from July 2008 to January 2009. Our objective was to develop new technological approaches, based on fuzzy logic control, to integrate into novel automated equipment for recirculation aquaculture systems used for fish production under intensive conditions. This technique allows farmers to incorporate their knowledge and experience into the control system. The results demonstrated a substantial water savings of 97.42%. There was a total fish biomass production of 1,655.3 kg and an average feed conversion rate of 1.55. The environmental variables were kept within acceptable ranges for tilapia production. We conclude that it is possible to increase the productivity and profitability of aquaculture systems, by applying new approaches based on modern control techniques, such as fuzzy logic control, that promote resource optimization.     

The effects of photothermal manipulation on reproductive development in female haddock Melanogrammus aeglefinus L.

Haddock (Melanogrammus aeglefinus L.) were maintained on either simulated natural (SNP) or advanced, phase‐shifted photoperiods (ADV) and reproductive characteristics of female fish were measured throughout two reproductive cycles. By advancing the seasonal photoperiod 8 weeks, relative to ambient conditions, follicle development, peak levels of estradiol and initiation of spawning were all accelerated compared with fish maintained on an SNP. Profiles of steroid synthesis and follicular development were similar between the two groups but the spawning period was protracted by 40 days in the fish maintained on ADV. Ultrasound imaging proved to be an effective and non‐invasive tool for accurately assessing ovarian development throughout the reproductive cycle. These results suggest that photoperiod manipulation has significant potential for extending the availability of eggs and larvae for haddock aquaculture.     

Egg hatching rate and fatty acid composition of Acartia bilobata (Calanoida,Copepoda) across cold storage durations

To investigate egg storage capacity of the copepod Acartia bilobata for aquaculture interest, we tested hatching success rate (HSR) of inclusive eggs (mixture of all egg types) after 4°C storage. The HSR peaked after 14 days storage when incubating at 28°C for 48 hr (85.8 ± 1.6%) and 72 hr (87.6 ± 0.9%), then gradually declined until 1 year (48 hr: 7 ± 0.6%; 72 hr: 19.4 ± 3.9%). Reallocation of fatty acid profile suggests that docosahexaenoic acid (DHA) is correlated with the HSR of A. bilobata eggs. Additionally, we investigated the HSR of diapausing eggs (unhatched eggs after 72 hr incubation of the inclusive eggs) after 4°C storage. Their HSR peaked after 14 days storage (48 hr:75.3 ± 3.5%; 72 hr:78.2 ± 2.1%), then gradually declined until 60 days (48 hr HSR:42.1 ± 2.3%; 72 hr HSR:53.0 ± 3.2%). Overall, we illustrated the hatchability of diapausing and quiescent eggs of A. bilobata after 4°C storage. The cold storage capacities were low (<60% HSR after 60 days), and it could be limited by the egg DHA content. Our findings provide implications for future studies aiming to improve cold storage techniques of tropical copepod eggs for aquaculture applications.     

Historical aspects, current status and prospects of pejerrey aquaculture in South America

The pejerrey Odontesthes bonariensis (Valenciennes, 1835) is an inland water fish from the Pampas region comprising part of Argentina, Uruguay and the South of Brazil. Pejerrey is a very popular fish in this region and has a long history of domestic and international introductions, which attests to the high quality and market value of its flesh, as well as its attractiveness as a game fish. The desirable characteristics of pejerrey also make it a good candidate for aquaculture, and the first trials on pejerrey cultivation (atheriniculture) were started more than a century ago in Argentina. In spite of the considerable interest in its development, little progress has been made and atheriniculture is still restricted to propagation and stocking for sport fishing purposes. In this review, we summarize the history of atheriniculture and the biological, technological, scientific, cultural and infrastructural constraints to pejerrey aquaculture development thus far. We also suggest possible scenarios of pejerrey aquaculture development compatible with the socio–economic conditions of South American countries. Our projections also take into consideration recent scientific findings on the biology of pejerrey and technological advances in seafood processing, storage and transportation, as well as the latest trends of seafood consumption and international markets. The best production strategy remains to be determined by trial and error but it is likely that, initially, production should focus on a differentiated, high‐quality fish for the premium or international markets rather than attempting to compete with the cheap fish from natural sources. An international cooperation project with Japan has successfully demonstrated the feasibility of breeding pejerrey in captivity and mass producing seeds efficiently in Argentina, and has provided the foundation for the development of intensive and extensive farming of this species.     

Diphasic sedimentation technique complemented by a statistical approach as a useful tool to the quantification and the determination of dynamics of eggs produced by adult monogenean parasitizing groupers,Epinephelus marginatus (Lowe, 1834), in captivity

Monogenean parasites create problems in confined fish, such as at aquaculture and aquariums facilities. Strategic timing of antihelminthic treatments should be based on the dynamics of monogenean egg production which requires egg quantification, but there is no standardized analytical method. The WHO diphasic sedimentation method for helminth quantification of eggs was applied in samples with tetrahedral and fusiform monogenean eggs from six specimens of confined groupers (Epinephelus marginatus) (31 m³ sea water tank; water temperature 21.1–14.4°C; photoperiod 9:53–15 h light; November 2011 to June 2012). Helminth eggs remain in the pellet, while most organic matter was removed forming a cap. In contrast, monogenean eggs are distributed within both the pellet and cap. The diphasic sedimentation method is suitable to quantify tetrahedral and total egg number by counting those eggs in the pellet and incorporing water temperature data to obtain a statistically significant model expression (R² = 0.943; R² = 0.809), while this approach only weakly predicted fusiform egg numbers (R² = 0.297). Fusiform egg numbers declined along November–December, and increased in February–March, until June. Tetrahedral eggs decreased in November–December, but did not increase until March. The trend of egg populations and best time for antihelminthic treatment application can be set by WHO technique with the statistical approach proposed.     

Growth and survival of olive barb,Puntius sarana (Hamilton 1822) larvae produced with cryopreserved versus fresh sperm

Despite the success in fertilization and hatching of fish eggs with cryopreserved sperm, report on growth and survival of larvae produced from frozen‐thawed sperm is inadequate. The study evaluates the applicability of cryopreserved sperm for mass seed production by comparing the growth and survival of a popular food‐fish olive barb, Puntius sarana (Hamilton 1822) larvae produced from cryopreserved and fresh sperm. The eggs were artificially fertilized with cryopreserved and freshly collected sperm, and the growth and survival of produced larvae from both group recorded up to 12 weeks. The independent sample t‐test statistic showed the difference in lengths, t(718) = 0.241; P = 0.810 and weights, t(718) = 0.412; P = 0.680 were insignificant between two groups. There was also no significant difference, t(718) = ?0.758, P = 0.448 in survival of larvae produced from cryopreserved and freshly collected sperm. The study indicates that larvae of olive barb produced from cryopreserved sperm are equally compatible in growth and survival as the larvae produced from fresh sperm. Therefore, cryopreserved sperm can be applied for artificial fertilization of P. sarana to supply quality seed for aquaculture.     

Water temperature,time of exposure and population density are key parameters in Enteromyxum leei fish-to-fish experimental transmission

Enteromyxum leei is a myxozoan histozoic parasite that infects the intestine of several teleost fish species. In gilthead sea bream (Sparus aurata), it provokes a chronic disease, entailing anorexia, delayed growth, reduced marketability and mortality. Direct fish-to-fish transmission, relevant in aquaculture conditions, has been demonstrated for E. leei via effluent, cohabitation, and oral and anal routes. However, the minimum time of exposure for infection has not been established, nor the possible effect on the fish immune response. Two effluent trials were performed at different temperatures (high: average of 25.6°C; and low: constant at 18°C), different times of exposure to the effluent (1, 3, 5 and 7 weeks) and different population densities. The results showed that 1 week was enough to infect 100% of fish at high temperature and 58.3% at low temperature. High temperature not only increased the prevalence of infection in posterior intestine, but also induced a higher production of specific antibodies, limiting the progression of the infection along the intestine. Longer time of exposure to the parasite and higher fish densities facilitated E. leei infection. These results show that effective diagnosis, lowering animal density and removal of infected fish are key aspects to manage this disease in aquaculture facilities.