Effects of on‐demand feeding on sea urchin larvae (Paracentrotus lividus; Lamarck, 1816), development,survival and microalgae utilization

This study compared the growth of sea urchin Paracentrotus lividus larvae cultured using two different rearing methods: a variable method based on a variable amount of feed (microalgae) and seawater exchange (30% or 50%) established according to the phytoplankton concentration in the larval cultures and a fixed method characterized by a fixed amount of feed and seawater exchange. Three microalgae diets, Isochrysis sp. (Tahitian strain, T‐Iso), Chaetoceros gracilis and a 50:50 mixed diet, were tested with both rearing methods. Larval development and survival were assessed at the 6‐arm pluteus stage (P6), competence (Cp) and metamorphosis (Mt). Data showed that the variable method reduced the requirements for phytoplankton and seawater exchange. Indeed, through the optimization of feed rations, it was possible to reduce the production of debris and settled phytoplankton, minimizing the need for water exchanges. Higher larval survival resulted at Cp and Mt stages for those reared with the variable method as opposed to the fixed one. Survival and development were also influenced by the tested dietary treatments: at Mt stage, the mixed diet resulted in a higher larval survival (63.3 ± 8.9%) than T‐Iso (19.7 ± 12.1%) and C. gracilis (23.4 ± 15.1%) (P < 0.05). These results suggest that the use of the variable method improves the larval survival and development and also it reduces resource consumption (phytoplankton, seawater use and work effort), which in turn could potentially improve the hatchery production of P. lividus.     

The use of diatom Skeletonema costatum on aquaculture‐produced purple sea urchin (Paracentrotus lividus) larvae and post‐larvae diet

The quality of the microalgae provided on Paracentrotus lividus larvae rearing is a primordial factor having a direct (nutritional properties) and indirect (water quality) impact on growth, competence and survival. Skeletonema costatum is a diatom commonly used in the bivalve cultivation. However, the use of this diatom in P. lividus larval cultivations is poorly known. The Rhodomonas spp. is a microalgae commonly used in sea urchin larvae culture. Three different diets were tested on P. lividus larvae and post‐larvae cultivation (D1—Rhodomonas marina, D2—S. costatum, D3—mixture of both algae). Larvae fed with the D2 diet (55.8%) and D3 (39.9%) had a survival at 15 DAH higher than D1 (5.5%). The low survival in D1 could be due to the higher microbiological load on microalgae (Vibrio alginolyticus and V. pectenicide). Larvae fed with S. costatum (D2) showed a lower development than other diets. The competency index was lower for larvae fed with the D2. These results show that microalgae diversified diets contribute to a better development of P. lividus larvae. During the settlement and post‐settlement phase, there was also a lower growth of the sea urchin fed with the D2 and a higher survival for D3.     

Increasing the stocking density in Paracentrotus lividus larviculture: Effects on survival and metamorphosis rates

The development of sustainable methods for sea urchin juvenile production is currently constrained by high mortality rates during larval growth and the high costs of larval rearing systems management. With the aim of developing a method for the production of juveniles of the purple sea urchin Paracentrotus lividus in a medium‐scale recirculating system, the present study focused on the effects of high stocking densities on larval growth. Plutei larvae were reared at three different densities (up to 7 ind/ml) in a semi‐static culture system. Larval survival and metamorphosis success were evaluated in order to identify the most effective density range. The highest metamorphosis rates (80%–95%) were obtained at 4 and 7 larvae/ml. These results are comparable with (and in some cases higher than) those reported for the same species at much lower larval densities. In conclusion, the rearing conditions tested here show for the first time that a significantly higher (4 ind/ml) stocking density than those of traditional P. lividus rearing methods (based on large volumes and low densities) can be adopted, thus supporting the feasibility of an increase in the final output of competent larvae with no increase in rearing volumes.     

Gonad quality of sea urchin Paracentrotus lividus cultured in an offshore pilot‐scale trial on the south‐east Italian coast

A pilot project aimed at testing roe enhancement strategies based on offshore Paracentrotus lividus cultures was conducted off the south‐east coast of Italy (Apulia Region). Adult sea urchins were reared in sea cages located 700 m offshore at a depth of 12 m for 3 months. The animals were fed once a week on two formulated diets, prepared mixing nutrients with agar 20 g/Kg and differing only in terms of the protein source: anchovy flour (Diet A) or krill flour (Diet K). At the end of the rearing trial, the gonad somatic index of sea urchins fed on formulated diets significantly exceeded that of wild sea urchins. Total FAA content in the gonads of wild sea urchins and Diet A‐fed sea urchins was similar, whereas in Diet K‐fed sea urchins it was significantly higher. In terms of fatty acids, the gonads contained SFAs, MUFAs and PUFAs. In visual and sensory assessment of gonads by panel test and electronic nose, the gonads of reared sea urchins were rated as being of better size, while no differences were recorded for coloration, taste and odour. This study shows that under these experimental conditions, commercial‐grade Paracentrotus lividus roe enhancement can be achieved after 3 months in sea cages.     

Influence of broodstock diet on somatic growth,fecundity, gonad carotenoids and larval survival of sea urchin

The effects of formulated feeds on Paracentrotus lividus broodstock performances and carotenoid compositions were investigated. Performance of offspring derived from each dietary treatment was compared to determine whether maternal provisioning of nutrients affected offspring development and survival under commercial culture conditions. At the end of the experimental period (3 months), urchins were induced to spawn, relative fecundity measured, and offspring derived from each treatment were reared independently and survival up to competence assessed. Carotenoid composition of the gonads was also measured. Data showed that the highest dietary protein content significantly improved somatic growth, whereas higher lipid content increased gonadal index (GI) consistent with the use of gonads as nutrient storage in sea urchins. Nonetheless, gonad lipid concentration was not significantly different between treatments indicating that higher dietary lipid content favoured gonadal size rather than increase lipid content of the gonadal tissue. Interestingly, GI and fecundity were not correlated, although the latter may have been enhanced by dietary xanthophyll. This suggests the importance of including carotenoids in broodstock diets to enhance hatchery outputs. This study also indicated that, although broodstock diet can influence fecundity, it had no significant impact on larval survival, which could instead be influenced by rearing conditions.     

Evaluation of dried macrophytes as an alternative diet for the rearing of the sea urchin Paracentrotus lividus (Lamarck, 1816)

The aim of this work was to assess the potential use of different dried macroalgae as food in the rearing of Paracentrotus lividus. Growth, consumption and food conversions were compared in adult sea urchins fed with fresh or dried thalli of four macroalgae species. Six experimental diets were tested: (a) fresh Palmaria palmata; (b) fresh Saccharina latissima; (c) dry P. palmata; (d) dry S. latissima; (e) dry Laminaria digitata and (f) dry Grateloupia turuturu. Linear growth rates were similar for all treatments. Specific growth rate was higher in sea urchins fed with fresh P. palmata, but no difference was found between animals fed with fresh S. latissima and those fed with dried diets. Regarding daily food consumption (DFC), sea urchins consumed the same amount of dried macroalgae as fresh but exhibited a higher food conversion efficiency (FCE) when fed with fresh P. palmata. However, this FCE was only significantly higher when compared to sea urchins fed with dry L. digitata. Dried G. turuturu is not a suitable diet due to its rapid degradation after rehydration. The results suggest that P. lividus adults can be reared on dried macroalgae thalli without detriment to their somatic growth, especially over short periods. The low cost of feeding sea urchins with this diet could help small shellfish farmers to diversify their production into echinoculture.     

Protein content and amino acid composition of eggs and endotrophic larvae from wild and captive fed sea urchin Paracentrotus lividus (Echinodermata: Echinoidea)

Knowledge on the biochemistry of proteins and amino acids (AA) of eggs and larvae of echinoids is scarce and the possibility to modify their profiles by diet manipulations is unknown. The protein content of eggs, prisms and pre‐plutei and the amino acid composition of eggs of Paracentrotus lividus from captive broodstock fed prepared diets were analysed and compared with the ones obtained from wild broodstock. Diets differed on protein source (fish or soy meals) and on protein content (10–40% dry weight – DW). Total and soluble protein content of both eggs and larvae was higher than 400 g kg^?1 DW and 200 g kg^?1 DW respectively. Glycine was the most abundant free AA. Very few differences were found among P. lividus eggs and larvae biochemical parameters, suggesting that their AA composition can hardly be changed by broodstock diet manipulations.     

Protein and energy digestibility and gonad development of the European sea urchin Paracentrotus lividus (Lamarck) fed algal and prepared diets during spring and fall

Protein and energy are two of the main limiting factors for sea urchin growth. However, the requirement of daily protein and energy to maximize gonadal production is still unknown. Paracentrotus lividus were fed three experimental diets: Ulva lactuca, Gracilaria conferta and a prepared diet for 2 months in the fall of 1999 and spring of 2000. Sea urchins from a laboratory‐cultured population of equal age, weight and test diameter were used. Apparent digestibility coefficients (ADC%) for protein and energy, using acid‐insoluble ash as a marker, were measured for all experimental diets. Apparent digestibility coefficients for protein was high (>75%) for all diets. Energy digestibility varied among the diets and was lowest for G. conferta (50–62%). The three diets contained varying digestible protein (DP) to digestible energy (DE) ratios of 25, 26 and 12 mg kJ^?1 for U. lactuca, G. conferta and the prepared diet respectively. Digestible protein intake was similar for all treatments, but DE intake was greater for sea urchins fed the prepared diet in both seasons. As a result, the gonad production was significantly higher for urchins fed the prepared diet, suggesting that energy was limiting in the algal diets. Paracentrotus lividus spawned during the spring experiment, resulting in protein loss in all treatments. Protein loss was lowest in the sea urchins fed the prepared diet. Enhanced gonadal growth and gamete development of P. lividus resulted from the higher dietary energy content of the prepared diet.     

Preservation of black sharkminnow,Labeo chrysophekadion (Bleeker, 1849) spermatozoa

The objective of this study was to investigate the effects of extenders and storage time on motility, viability and fertilization of preserved black sharkminnow, Labeo chrysophekadion spermatozoa. Sperm were diluted 1:3 in one of five extenders: modified Cortland solution (MC); Hanks' balanced salt solution (HBSS); 0.9% sodium chloride (NaCl); Kurokura solution (KU); and modified extender, and undiluted sperm samples were used as control and stored at 4°C for 5 days. Motility, viability and fertilization rates were evaluated every day. After a storage time of three days, the highest motility, viability and fertilization rates (61.27 ± 2.26%, 58.60 ± 2.29% and 40.58 ± 0.57, respectively) were achieved with sperm diluted with modified extender. Motility, viability and fertilization rates decreased significantly (P < 0.05) with increasing storage time in all treatments. In addition, this study found that motility, viability and fertilization had a positive significant correlation (P < 0.01). The results indicate that isotonic extender is suitable for the short‐term preservation of black sharkminnow spermatozoa.     

Experimental rearing of the sea urchin Paracentrotus lividus fed with discards of the lettuce Lactuca sativa in a sea‐based system

Small‐sized specimens (test diameter: 16.64 ± 0.93 mm, mean ± SE) of the sea urchin Paracentrotus lividus were fed with fresh discards of the lettuce Lactuca sativa during a 24‐week experiment in a sea‐based system. At the end of the experiment, stock survival was high (88.8 ± 6.6%). Sea urchin test diameter and total weight grew by 35% and 56%, respectively, while gonad somatic index, after an initial decrease, increased by 3.2%. Moreover, more than 90% of specimens achieved the gonad colour that the market demands. These results support the exploitation of L. sativa as the main ingredient in a manufactured diet for echinoculture of P. lividus. Employing diets formulated with discard ingredients, combined with a low‐cost sea‐based rearing system, could be a suitable approach for sustainable management of echinoculture.     

Motility and fertility of cryopreserved spermatozoa of the Japanese sea cucumber Apostichopus japonicus

We developed both a cryopreservation method for Japanese sea cucumber spermatozoa and an artificial fertilization method using post‐thaw spermatozoa. Twenty per cent dimethyl sulfoxide (DMSO), 16% foetal bovine serum, and 64% artificial seawater were suitable cryodiluent, and the diluent was pre‐cooled to 0°C. Semen was diluted with the solution and enclosed in a 250 μl straw, cooled to ?50°C at 10.4 ± 0.4°C/min, and immediately immersed in liquid nitrogen. Although this method showed the highest post‐thaw motility in all the conditions we examined, its post‐thaw motility was still less than approximately 15%. Artificial fertilization was carried out by adding post‐thaw semen with a cryodiluent to the oocytes. The fertilization rate of 200 oocytes/ml seawater increased with the amount of post‐thaw semen from 1 to 5 μl but showed a significant decrease at 25 μl. This decrease was considered to be due to DMSO in the cryodiluent, because the fertilization rate of the fresh semen decreased sharply when the DMSO concentration around the oocytes was 1.0% or more. Further improvement in increasing post‐thaw motility and lowering the cryoprotectant concentration is necessary for commercial‐scale artificial fertilization.     

Carotenoid composition of a New Zealand (Evechinus chloroticus) and an Australian (Heliocidaris erythrogramma) sea urchin in relation to gonad colour

Sea urchins are commercially harvested for their edible gonads, also known as roe or uni. Most species, particularly those from the Northern hemisphere are reported to exhibit limited variation in gonad colour, which is proposed to be due to carotenoid pigments. The commercially harvested species from New Zealand, Evechinus chloroticus, and from Australia, Heliocidaris erythrogramma, however, exhibit considerable gonad colour variation, ranging from a culinary desirable light yellow/orange to an undesirable brown. Gonads from E. chloroticus and H. erythrogramma were characterized spectrophotometrically and the carotenoid content extracted and analysed by reversed‐phase high‐performance liquid chromatography. The main carotenoid found in the gonads of both species was 9′‐cis‐echinenone, with lower levels of all‐trans‐echinenone, lutein and isozeaxanthin. Carotenoid composition contributed to the yellow/orange colour components of the gonads, but was not correlated with the darker roe coloration observed in some E. chloroticus individuals. Our results highlight important considerations relating sea urchin gonad coloration to carotenoid content and as such will provide useful information for the future aquaculture and processing of these two species.     

Trial grow‐out culture of sea cucumber Holothuria scabra in sea cages and pens

Field trials were conducted to determine the effects of size, grow‐out period and site on the growth and survival of Holothuria scabra. Juveniles were reared in sea cages in two sites for 2 months during two different times of the year. Juveniles from Experiment 1 were subsequently grown in sea pens for 8 months in one site. The significantly lower survival particularly of the small‐sized group (<0.1 g) in Pilar is likely due to reduced water and sediment quality because of proximity to fish‐farming activities. The importance of grow‐out period was evident in the significant differences in weight increments in all size groups and biomass in the small‐sized group (P < 0.10) in Lucero during Experiment 2 when water temperature range and incidence of rainfall were higher. The decrease in the average weight of adults during the second half of the grow‐out period may be due to the interplay of the reduction in salinity, onset of sexual maturity and biomass exceeding carrying capacity in the pens. The estimated biomass threshold in the sea cages and pens in Lucero were 300 g m^?2 and 380 g m^?2 respectively. Implications of the results on the viability of small‐scale pen grow‐out culture are discussed.     

Effects of diet and temperature on post‐settlement growth and survival of the short‐spined sea urchin Strongylocentrotus intermedius

Effects of diet and temperature on post‐settlement growth and survival of a sea urchin Strongylocentrotus intermedius, which fed on one of six mono‐cultured benthic diatoms, gametophytes of a brown alga Undaria pinnatifida, a green alga Ulvella lens plus mixed benthic diatoms, or no food at 6, 9, 12 and 15°C, were examined. Digestion efficiency (DE), ingestion rate (IR), excretion rate (ER) and digested cell content index (DCCI) of each diatom species were measured. Growth rates largely differed among the dietary treatments from 7 days post‐settlement. Sea urchins fed on a diatom Cocconeis sublittoralis showed considerably higher growth (7.85‐34.67 μm day^?1) than those fed on the other diets and high survival rates (100%). DCCI was also highest in C. sublittoralis. These results suggest that the quantity of diatom cell contents digested is an important factor affecting growth and survival of the sea urchins. Growth rates of sea urchins were higher in higher water temperatures, and significant differences in growth rate were observed between 6‐9 and 12‐15°C. ERs of C. sublittoralis were generally higher at higher temperatures, but DEs did not differ among the temperature treatments. Variations in growth rate among different water temperature appear to be caused by different food intakes of the urchins.     

Feeding time,frequency and ration affect growth and energy allocation in young adults of the sea urchin Lytechinus variegatus

In a 62‐day growth trial, wild caught Lytechinus variegatus (ca. 18 g, 35 ± 2 mm dia.) were fed as follows: (i) ration equivalent to 3% of average body weight proffered once daily in the morning (AM treatment); (ii) ration equivalent to 3% of average body weight proffered once daily in the evening (PM treatment); (iii) ration equivalent to 1.5% of average body weight proffered twice daily (every 12 h, AM/PM treatment); (iv) ration equivalent to 3% of average body weight proffered in the evening on alternate days (EODSR/PM); or (v) ration equivalent to 6% of average body weight proffered in the evening on alternate days (EODDR/PM). At 30 and 62 days, wet weight gain among urchins fed daily was significantly higher than that of urchins fed on alternate days, regardless of ration size. At 62 days, reduced gonad dry matter production and gonad index were observed among individuals fed on alternate days, regardless of ration size. At 30 and 62 days, feed conversion ratio was optimized among individuals fed daily and in the EODSR/PM treatment. These data suggest that, for culture of L. variegatus, daily feeding will optimize growth, gonad production and feed efficiency regardless of ration size or time of feeding.     

The use of stable isotope ratios δ13C and δ15N to track the incorporation of Ulva and other important dietary ingredients into the gonads of the sea urchin Tripneustes gratilla

In this study, we demonstrate how stable carbon (C) and nitrogen (N) isotope analysis can be used to estimate the allocation of specific dietary ingredients, incorporated into four artificially formulated feeds supplemented with varying amounts of dried seaweed Ulva armoricana (0, 50, 150 and 200 g/kg), to the production of gonads by Tripneustes gratilla over a 20‐week growth trial. Results indicate that U. armoricana is an important dietary ingredient for gonad production, accounting for an average of 37.33 ± 1.03% of the isotopic signal recorded for gonads at the end of the growth trial. This is significantly more than fish meal and soya, which only contributed an average of 11.40 ± 1.81 and 3.80 ± 0.09%, respectively, of the isotopic signal of the gonads. Maize and wheat each account for almost 25% of all the dietary ingredients used to formulate the feeds, but their relative contribution to gonad production only averaged 8.55 ± 0.58 and 3.80 ± 0.05%, respectively, among the diets. This indicates that, at least for gonad development, these ingredients may not be required at such high levels. These findings support previous data on the importance of Ulva in abalone and urchin diets, and demonstrate the value of stable isotope analysis for assessing the contribution of specific dietary ingredients in new feed formulations, particularly where growth of specific tissues is being investigated.