Nikos Papandroulakis

Effect of water currents on the development of skeletal deformities in sea bass (Dicentrarchus labrax L.) with functional swimbladder during postlarval and nursery phase

Abstract Lordosis in reared sea bass was previously related either to the absence of swimbladder, or to bad or late inflation of this organ when damages were irreversible. Our results prove that these explanations are insufficient and that similar deformations may occur frequently in fry with functional swimbladder during the early weaning phase, if currents in tanks are higher than 10 cm s −1 .

Mesocosm: a reliable technology for larval rearing of Diplodus puntazzo and Diplodus sargus sargus

Species diversification is today considered as a major issue for the sustainable development of the Mediterranean aquaculture. For successful propagation of any species however, larval rearing is considered a bottleneck and therefore the development of appropriate tools is essential. Mesocosm is a semi-intensive technology that facilitates larval rearing of several species integrating principles of both intensive and extensive aquaculture, which solves biological problems and many of their technical, human and economical consequences. The extensive (and now even the semi-extensive) strategy is used in the most critical segments of the rearing process during the early developmental stages, when larvae are still extremely weak, sensitive to intensive environment, easily stressed and difficult to feed. The intensive strategy is used as soon as larvae are considered mature enough to be reared easily using classical methods. The technology was used for the rearing of two species, with potential for aquaculture, the sharpsnout seabream (Diplodus puntazzo) and the white seabream (Diplodus sargus sargus). Three groups of each species were monitored for a period of 50–70 days post hatching. Survival for both species was about 54% at the end of the trials. Sharpsnout seabream larvae reached 19.6 ± 0.9 mm total length and 107.2 ± 31.9 mg body weight 50 days post hatching. White seabream larvae 60 days post hatching reached 32.7 ± 2.7 mm total length and 450 ± 70 mg body weight. In order to verify the economical viability of the technology, the individual production cost for each species was estimated and reached ¢0.027 for white seabream and ¢0.043 for sharpsnout seabream. Results indicate the reliability of the technology for the larval rearing of the two species.

Evaluation of transportation procedures on water quality and fry performance in red porgy (Pagrus pagrus) fry

Abstract The effect of stocking density (10, 20, 30, 40 kg/m3), water renewal (0% or 100% renewal rate per hour), hauling temperature (14, 19, 24 °C), salinity (20, 25, 30, 35, 40 psu), and use of anaesthesia (0, 10, 20, or 50 ppm ethynelglycol-monophenylether) prior to transportation on red porgys fry performance, liver glycogen, and water quality parameters was tested to evaluate transportation procedures in a promising candidate for aquaculture. Simulated transport was performed in plastic containers (volume 60 l) for 48 h. Water samples were taken at 4-h intervals after transport for the determination of pH, carbon dioxide (CO2), un-ionised ammonia (NH3) and ammonium (NH4+). Additionally, liver samples were collected at 4 and 48 h for glycogen determination. There were no statistically significant fluctuations in dissolved CO2 concentration in all tested conditions. Stocking density did not affect NH3 and NH4+ average values and hepatic glycogen content in groups exposed to a water renewal rate of 100%, while increasing NH3 and NH4+ average values with increasing stocking density was observed in groups with no water renewal. Under the same stocking density, a significant change in NH3 and NH4+ fluctuations over the duration of the experiment was observed with concentrations increasing, with a mean exponential rate (±SD) of 0.060±0.005 (NH3) and 0.062±0.005 (NH4+) per hour in groups with no water renewal, and −0.033±0.004 (NH3) and −0.024±0.007 (NH4+) per hour in groups with 100% water renewal. Water temperature affected significantly the hepatic glycogen content and survival during transport. There was no significant effect of salinity and anaesthetic (except at a dose of 50 ppm) on fry survival and on the water quality parameters. It is suggested that red porgy should be transported in stocking densities of 20–25 kg/m3 and at a hauling temperature similar to that kept at the exporters fish rearing tanks (preferable 19 °C). Besides, it is recommended to avoid temperature differences between the hauling water and the water used for renewal during fry transportation.

Enhanced biological performance of intensive sea bream (Sparus aurata) larviculture in the presence of phytoplankton with long photophase

Abstract Sea bream larvae were reared under intensive conditions either with (pseudo-green water technique) or without (clear water technique) the addition of phytoplankton in the rearing tanks, under 24- or 18-h photophases. Phytoplankton presence in the rearing medium resulted in 44±17% survival and individuals of 2.0±0.2 mg wet weight after 20 days of rearing. With the clear water method, both survival and growth decreased to 16±6% and 1.1±0.2 mg, respectively. The daily consumption rate (as milligram of carbon consumed per milligram body carbon) at the beginning of exogenous feeding was 0.5 day −1 for all experimental conditions. At later stages, individuals reared with phytoplankton present had a daily consumption rate of about 0.7 day −1 , while those reared with the clear water technique presented consumption rates from 1.0 (for 24-h photophase) to 1.9 day −1 (for 18-h photophase). The mean food assimilation efficiency of the larvae, expressed as a Food Conversion Index (FCI), was between 6.3±1.4 (for 18-h photophase) and 8.2±1.2 (for 24-h photophase) for the individuals reared in the presence of phytoplankton. For larvae reared using the clear water technique, FCI was between 12.8±2.4 (for 24-h photophase) and 20.1±5.3 (for 18-h photophase).

The pseudo-green water technique for intensive rearing of sea bream (Sparus aurata) larvae

The “pseudo green water” technology for sea bream(Sparus aurata) larval rearing was evaluated by analyzingresults of a 2-year study, performed in a pilot scale system. Thetechnology is characterized by the daily addition of phytoplankton in therearing tanks during the first month of rearing. Effects of egg origin,spawningseason and initial larval density on the larval rearing were investigated. Fishreared in “pseudo green water” systems for 60 days, presented highbiological performance in terms of survival (56 ± 16%), meanweight (62 ± 12 mg), total length (20 ± 1mm), conformity with wild standard (88 ± 9%), andfunctional swim bladder (93 ± 4%). The results present homogenitybetween the categories (origin of eggs, time of spawning, initial egg density)studied, proving the stability of the technology.

The sex-specific transcriptome of the hermaphrodite sparid sharpsnout seabream (Diplodus puntazzo)

BackgroundTeleosts are characterized by a remarkable breadth of sexual mechanisms including various forms of hermaphroditism. Sparidae is a fish family exhibiting gonochorism or hermaphroditism even in closely related species. The sparid Diplodus puntazzo (sharpsnout seabream), exhibits rudimentary hermaphroditism characterized by intersexual immature gonads but single-sex mature ones. Apart from the intriguing reproductive biology, it is economically important with a continuously growing aquaculture in the Mediterranean Sea, but limited available genetic resources. Our aim was to characterize the expressed transcriptome of gonads and brains through RNA-Sequencing and explore the properties of genes that exhibit sex-biased expression profiles.ResultsThrough RNA-Sequencing we obtained an assembled transcriptome of 82,331 loci. The expression analysis uncovered remarkable differences between male and female gonads, while male and female brains were almost identical. Focused search for known targets of sex determination and differentiation in vertebrates built the sex-specific expression profile of sharpsnout seabream. Finally, a thorough genetic marker discovery pipeline led to the retrieval of 85,189 SNPs and 29,076 microsatellites enriching the available genetic markers for this species.ConclusionsWe obtained a nearly complete source of transcriptomic sequence as well as marker information for sharpsnout seabream, laying the ground for understanding the complex process of sex differentiation of this economically valuable species. The genes involved include known candidates from other vertebrate species, suggesting a conservation of the toolkit between gonochorists and hermaphrodites.

Biological Performance of Red Porgy (Pagrus pagrus) Larvae under Intensive Rearing Conditions with the use of an Automated Feeding System

Pagrus pagrus is one of the promising species for the industry in the Mediterranean but its rearing is still far from satisfactory. In the present work, the conditions and results of larval rearing with the use of an automatic feeding system are presented. Eight populations were reared for 20 days with the ‘pseudo green water’ methodology in two successive trials. Larvae were fed enriched rotifers during the entire rearing period, a mixed diet of rotifers and Artemia (Instar I when larvae reached 5 mm in length, replaced by Instar II after larvae reached 5.5 mm) and a formulated diet (after day 16 post hatching). A computerized system for feeding management was used. A total of 388,000 eggs were incubated and after 20 days, 237,973 larvae (TL = 6.96 ± 0.17 mm) were produced with a survival rate of 61.4 ± 6.3%. Individuals grew in terms of wet weight with an exponential rate of 0.167 ± 0.008 daily (R2= 0.983) with no variations between replicates. Mean individual daily consumption at first feeding (day 4-post hatching), was 0.20 ± 0.06 mg of food (0.03 ± 0.01 dry weight), that is, 180–300 rotifers, while on day 20, consumption increased by 10 (2.081 ± 0.106 mg and 0.276 ± 0.014 in wet and dry weight, respectively). When compared with sea bream, consumption was higher by approximately 3–4-fold. The mean food conversion ratio of the experimental period was 4. In comparison with sea bream larviculture, food consumption of red porgy is higher, and a different feeding strategy is required to satisfy the requirements of the larvae.

An automated feeding system for intensive hatcheries

Abstract The continuous on-line meeting of metabolic demand via feed supply is an important factor for successful aquaculture. This factor is more acute for small larvae, which have a relatively high metabolism, implicating a long photophase and continuous feeding. Such requirements can not be easily met using classic manual feeding methods due to logistic problems. A computerized system has been developed for feed management in intensive hatcheries. The daily plankton requirements of larvae, organized in feeding tables together with a distribution pattern, was used for the development of the required hardware and software to control feeding. The system computes the food required (plankton organisms) and activates a peristaltic pump and solenoid valves for distribution to tanks. The system offers the option of feeding either according to tables or manually, depending on the concentration of plankton in the rearing tanks. Feeding is programmable for 24-h periods. A pilot scale application gave comparable results from a biological perspective and improved management when compared with standard methodologies. Four populations of sea bream (Sparus aurata) were reared with the pseudo-green water intensive method using the automated feeding system and two were reared using a standard technique. Larvae in both cases reached a total length of 10.73±0.77 mm in 30 days post hatching with survival varying between 41 and 51% without differences between the conditions tested. In terms of management, the labor requirement for feeding was reduced by 30–40% with the use of the automated feeding system while the utilization of Artemia nauplii was reduced by 40%. Feeding data as well as information concerning growth of the larvae and the evolution of the rearing were collected in a database. The system is compatible with other software packages for data collection and retrieval.

Ontogenesis of the HPI axis and molecular regulation of the cortisol stress response during early development in Dicentrarchus labrax .

The cortisol stress response and the molecular programming of the corticoid axis were characterized for the first time during early ontogeny in a Mediterranean marine teleost, the European sea bass (Dicentrarchus labrax). Sea bass embryos, pre-larvae and larvae at specific points of development were exposed to acute stressors and the temporal patterns of cortisol whole body concentrations and the expression of genes involved in corticosteroid biosynthesis, degradation and signaling were determined. Expression of genes (gr1, gr2, mr, crf) involved into the corticoid response regulation combined with histological data indicated that, although a cortisol stress response is evident for the first time around first feeding, a pattern becomes established in larvae at flexion until the formation of all fins. Moreover, mRNA transcript levels of 11β-hydroxylase and 11β-hsd2 showed a strong correlation with the whole body cortisol concentrations. Concluding, our data reveal the presence of an adaptive mechanism in European sea bass at early ontogeny enabling to cope with external stressful stimuli and provide a better insight into the onset and regulation of the stress response in this species.

Severe mortality in mesocosm-reared sharpsnout sea bream Diplodus puntazzo larvae due to epitheliocystis infection.

This paper describes severe mortalities recorded in sharpsnout sea bream Diplodus puntazzo larvae reared in mesocosms. The mortalities were attributed to epitheliocystis infection. The pathology associated with the disease is described using histological techniques. Microscopical examination showed a massive infection of the skin, fins, and oral cavity, with impaired feeding, respiration, and osmoregulation being the most likely cause of death. This is the first report of epitheliocystis disease in sharpsnout sea bream and in fish at such an early developmental stage.