Sea Urchin Aquaculture Research Articles

A sustainable no-kill sea urchin aquaculture method to obtain caviar

A sustainable no-kill sea urchin aquaculture method to obtain caviar

Evaluation of sustainable feeds for “caviar” production in the Mediterranean sea urchin Paracentrotus lividus (Lamarck, 1816)

To improve the sustainability of aquaculture practices, a step towards the use of alternative nutrient sources (such as food processing discards) may secure the future of aquaculture sector, namely for emergent species, such as sea urchins. In this context, adult females of the commercial sea urchin Paracentrotus lividus were reared using four feeds based on lettuce discards (72%) and enriched (8%) with an animal-source ingredient (fish Sardina pilchardus, Feed-S; krill Euphausia superba, Feed-K; mussel Mytilus galloprovincialis, Feed-M; anchovy Engraulis encrasicolus discards, Feed-AD). A fifth feed, used as control treatment, was composed of macroalgae (Laminaria sp. and Ulva sp., Feed-UL). Feed performance was evaluated employing a new productive protocol, the Raking method, which propose testing feed effects on sea urchin caviar (oocytes rather than gonads) production. Thus, ingestion rates and absorption efficiency were measured to evaluate feed palatability. Somatic growth and caviar production, expressed introducing the ovosomatic index (OI) instead of the traditional gonadosomantic index, were measured to assess feed productive performances. Caviar quality was assessed by nutritional content and color. Ingestion rate results showed that all feeds were palatable, while findings on absorption efficiency showed differences between the five proposed feeds, with Feed-M and Feed-AD presenting the worst results. Somatic growth was promoted regardless the provided feeds, while OI resulted higher with Feed-K and Feed-M than the other feeds. All produced caviar resulted suitable for human consumption with high protein and fatty acid content, but caviar produced by Feed-UL showed the poorest nutritional profile. Similarly, Feed-UL led to the production of caviar with the lowest quality color, while Feed-S showed the best orange color. Lettuce-based feeds were therefore effective for feeding P. lividus as they stimulated production of high quality caviar. Findings support the exploitation of food discards for the production of eco-friendly feeds for sea urchin aquaculture.

Shipping live sea urchins: Effects of temperature and exposure time on survival

Sea urchin aquaculture could offset declines in wild fisheries. The economic feasibility of sea urchin aquaculture may depend on farmers receiving premium prices for product transported live internationally to markets or processing facilities. Research into cost-effective methods of transporting live sea urchins out of water is scarce. In this study, to get a baseline of the temperatures experienced by sea urchins transported by air in the Indo-Pacific region, temperature loggers recorded temperatures in ‘cooler boxes’ containing the sea urchin, Tripneustes gratilla, packed and shipped in seawater or dry. We then examined the effect of time kept out of water (6, 12, 24, 48 h) and air temperature (chilled ∼4 °C, cooled ∼12 °C, or ambient ∼27 °C) on mortality, change in wet weight, and fitness (as measured using righting behaviour) of two sea urchins, T. gratilla and Heliocidaris erythrogramma. For both species mortality (15 days after the treatment) was low (0–20%) when held out of water for up to 24 h at 12 °C, but 100% died within 15 days when held out of water at 4 °C and 27 °C. Mortality increased (∼60%) for T. gratilla held out of water for 48 h at 12 °C, but remained at ∼20% for H. erythrogramma in the same treatment. Righting times were faster for urchins exposed to air at 12 °C than at 4 or 27 °C. The mass (fluid) lost by urchins was a key predictor of mortality with urchins losing a higher percentage of their mass during longer exposure periods at higher temperatures. T. gratilla frequently spawned after being out of water. To test packing strategies that could influence sea urchin health, T. gratilla were packed out of water at 28.6 °C for 12 h in sealed or open containers and in containers that drained off excreted fluid or retained fluid around the urchins. None of these treatments had an impact on mortality to 15 days, the amount of fluid lost, or righting activity. Our results indicate producers may be able to transport T. gratilla and H. erythrogramma dry for up to 24 h with little mortality as long as temperatures are maintained at ∼12 °C. Additional research into limiting the fluid loss of sea urchins while being shipped dry may improve survival during longer shipping periods.

Temporal dynamics of bacterial populations in recirculating aquaculture systems for sea urchin production

Introduction: Sea urchin aquaculture is a rising industry, and in consequence, there is a need to establish optimal culture parameters to ensure the health of the cultured animals.
 Objective: To evaluate the bacterial counts in the seawater of sea urchin (Arbacia dufresnii) aquaculture recirculating systems (RAS).
 Methods: The bacteriological water quality of two RAS containing sea urchins was determined. For approximately two months, weekly water samples were taken. The bacteriological quality was determined by counting total aerobic heterotrophic populations, lactic acid bacteria, enterobacterias and genus Vibrio. Physicochemical parameters were also measured.
 Results: There was no presence of disease or mortality. Enterobacteria and lactic acid bacteria were not detected from both RAS systems. The number of animals had an important effect on the observed difference in the count of total bacteria and Vibrio spp. In RAS 1 the maximum counts of total bacteria and Vibrio spp. were 2.8 x 105 ± 1.7 x 105 and 1.45 x 105 ± 3.6 x 104 UFC ml-1, respectively. In RAS 2 total bacteria and Vibrio spp. exhibited repetitive behavior over time influenced in part by water exchange and mainly by feeding. The results indicate that periodic water changes ensure a limited growth of bacterial strains as Vibrio and other bacteria.
 Conclusions: Our results suggests that the bacterial count levels recorded in this study can be used as a threshold or safety limit for Arbacia dufresnii aquaculture.

Nutrient enrichment and probiotics for sea urchin Anthocidaris crassipina larvae in captivity to promote large-scale aquaculture.

Sea urchin contains physiologically active substances, such as amino acids and unsaturated fatty acids, and an important aquatic organism. Purple sea urchin, one of the common edible sea urchins, is an important aquatic product. In order to supply the vast seafood market, large-scale aquaculture of sea urchins is very important. The aim of this study was to optimize the rearing of theAnthocidaris crassipina larvae enhancing the nutrition by mixing feed to improve their growth and survival. The survival rate of Chaetoceros muelleri feeding alone is only 40%. If the survival rate is improved through nutrient enrichment, the large-scale aquaculture of larvae can be promoted. The experiment was divided into two parts. Experiment 1: Two types of commonly used microalgae, Isochrysis galbana tml (I), C. muelleri (C) and two types of probiotics, Rhodopseudomonas palustris (R), and Saccharomyces cerevisiae (S) were used in the.Feeding amounts are 5000, 10,000, and 20,000 cell mL-1, and the control group (N) did not eat. Experiment 2: C. muelleri 20,000 cell mL-1 was mixed with I. galbana tml, R. palustris (R)and S. cerevisiae (S) at 5000 and 10,000 cell mL-1. After the experiment, body length, body width, stomach length, rudiment length, rudiment length, body composition, digestive enzymes and survival rate were measured to evaluate the best feed. The results showed that the mixed feeding of C. muelleri 20,000 cell mL-1 and R. palustris 5000 cell mL-1 can achieve the best development and survival of larval embryos and can promote metamorphosis into juveniles in the shortest time. The research results will be applied to the large-scale aquaculture of A. crassipina larvae to promote the diversity of aquaculture.

Effect of basket height and stocking density on production of the sea urchin Tripneustes gratilla: insights and recommendations

Basket height and stocking density are crucial and related factors for successful commercial sea urchin aquaculture, but these factors have not been definitively determined for production of Tripneustes gratilla. This study investigated the effects of varying basket heights (deep 30 cm vs. shallow 15 cm) and stocking densities (4, 6 and 8 kg.m−2 or 13, 19 and 24% coverage of available basket surface area) on aquacultural production of T. gratilla. Contrary to previous suggestions, reduced consumption was identified as the cause of decreased production in deeper baskets. Consumption was significantly higher in shallow baskets than deep baskets for both the fresh seaweed, Ulva lacinulata, (W = 38, p = 0.026) and formulated feed (W = 76.5, p = 0.007). Consequently, baskets of approximately 15 cm deep are recommended to enhance production of T. gratilla and possibly other urchin species. Two subsequent trials assessed production of T. gratilla at different stocking densities. Trial 1 aimed to maximize urchin size over a three-month grow-out period using fresh U. lacinulata, while trial 2 focused on enhancing gonad production over two months using formulated feed. Although greater stocking density significantly reduced the specific growth rates of individual urchin mass in both trials (p < 0.044), there was no significant impact on mortality, net production or gonad size and quality. The variations in growth rates were attributed to spine loss resulting from negative behavioural interactions (F2, 9 = 9.551; p = 0.005). Based on the objectives of both grow-out and gonad-enhancement phases, we recommend a stocking density of approximately 20% coverage.

Advances in Aquaculture Hatchery Techniques of Sea Urchin Sphaerechinus granularis (Lamarck, 1816) (Echinoidea: Toxopneustidae): Broodstock Conditioning and Spawning Induction.

In response to the growing demand for sea urchin gonads (roe or uni) in Asian and European markets and the concerns regarding the overexploitation of wild populations, this preliminary study addresses the need for cost-effective protocols in echinoculture. The primary focus of this research was to evaluate the gonadosomatic index (GI) in captive-conditioned Sphaerechinus granularis over a five-month period and compare it with that of their wild-caught conspecifics. Additionally, two different spawning induction methods were assessed: potassium chloride (KCl) injection and agitation. Results indicate that captive-conditioned sea urchins exhibit significantly higher GI values when compared to their wild-caught counterparts. Furthermore, it was observed that the agitation method is equally effective as the KCl injection in triggering a positive response, i.e., gamete ejection, while maintaining lower mortality rates among the subjected S. granularis. In conclusion, this preliminary study underscores the pivotal role of broodstock conditioning in supporting the sustainability of sea urchin aquaculture. Moreover, the spawning induction method through agitation emerges as a viable alternative to the traditional intracelomic KCl injection, offering comparable efficacy without compromising the survival of the broodstock. These findings have significant implications for the development of sustainable sea urchin farming practices.

Combining computer vision and standardised protocols for improved measurement of live sea urchins for research and industry

AbstractTo allow sea urchin aquaculture to achieve its intended scale, efficient and precise methods for measuring large numbers of urchins in commercial‐scale operations are needed. Current protocols for measuring urchin test (shell) dimensions and mass are time‐consuming and prone to high measurement error, thus inconvenient in research and impractical in a commercial context. This study investigates and compares various measurement methods with a newly developed computer vision approach developed in this study, to establish a single protocol using precise, efficient and accessible methodology for measuring live urchins. We show that urchin wet mass can vary up to 8.73% depending on time out of water; this is significantly reduced to an average of 0.1% change by allowing urchins to drip‐dry for at least 90 s prior to weighing. We found the conventional vernier calliper method used to measure urchin dimensions to be both time‐consuming and imprecise (mean coefficient of variation (CV) of 2.41% for Tripneustes gratilla). Conversely, the computer vision programme we developed measures with higher precision (mean CV of 1.55% for T. gratilla) and is considerably faster. The software uses a series of hue saturation value filters, edge detection algorithms and distortions to measure the diameter of the test (excluding spines) of multiple urchins at once. The software is open‐source, and the protocol does not require specialised equipment (can be performed with a mobile phone camera). When the computer vision application is combined with the simple procedures described in this paper, to reduce measurement inaccuracies, urchin wet mass and diameter can be more efficiently and precisely determined. For a larger scale context, this software could easily be incorporated into various tools, such as a grading machine, to completely automate various farm processes. As such, this study has potential to assist urchin data collection in both research and commercial contexts.

Blue-Green Algae as Stimulating and Attractive Feeding Substrates for a Mediterranean Commercial Sea Urchin Species, Paracentrotus lividus.

Sea urchins rely on chemical senses to localize suitable food resources, therefore representing model species for chemosensory studies. In the present study, we investigated the chemical sensitivity of the Mediterranean sea urchin Paracentrotus lividus to the blue-green alga Aphanizomenon flos-aquae, namely "Klamath", and to a few amino acids chosen from the biochemical composition of the same algae. To this end, we used the "urchinogram" method, which estimates the movement rate of the sea urchins in response to chemicals. Our results showed that Klamath represents a strong chemical stimulus for P. lividus as it elicits an overall movement of spines, pedicellariae, and tube feet coupled, in some cases, to a coordinated locomotion of the animals. Sea urchins also displayed a sensitivity, even if to a lesser extent, to leucine, threonine, arginine, and proline, thus implying that the amino acids contained in Klamath may account, at least in part, for the stimulating effects exerted by the whole algae. Additionally, our results show that Klamath, as well as spirulina, another blue-green alga with high nutritional value, is very attractive for this sea urchin species. These findings gain further importance considering the potential profit of echinoderms for commercial consumers and their growing role in aquaculture. Klamath and spirulina combine high nutritional profiles with attractive and stimulating abilities and may be considered potential valuable feed supplements in sea urchin aquaculture.

Dietary protein requirement for somatic growth and gonad production in the sea urchin Strongylocentrotus intermedius at different life stages

The rise in the demand for sea urchin aquaculture requires the optimization of dietary protein levels to maximize somatic growth and gonad production throughout the aquaculture process. This study aimed to investigate the dietary protein requirement for somatic growth and gonad production of the sea urchin Strongylocentrotus intermedius at different life stages considering protein leaching from diets during seawater immersion. Feeding trials were performed on three sizes of S. intermedius: S, small urchins prior to gonad differentiation; M, medium urchins following gonad differentiation; and L, large urchins close to the biological minimum size. Two feeding trials using diets with different gluten (protein source) levels (experiment I; 5, 10, 15, 20, 30, and 40%: experiment II; 0, 2, 4, 7, and 10%) were conducted for each size group. The diet ingredients were selected to minimize protein leaching, and the protein content of each diet was determined from the average content after immersion in seawater for 24 and 72 h. No significant differences were observed in the specific growth rate (SGR) of body weight in experiment I in all size groups. The SGRs of the body weight of urchins fed 4 and 7% gluten diets were significantly higher than those fed diets containing 0% gluten in experiments SII and MII, and a similar tendency was observed for SGRs for the body weight and test diameter of large urchins. Gonad indices of sea urchins increased with an increase in dietary protein content in experiments MII and LII, and the gonad indices of urchins fed 15 and 20% gluten diets were significantly higher than those fed 5% gluten diet in experiments MI and LI. Broken-line regression analyses on urchins in experiment II estimated the protein requirement for somatic growth to be 2% regardless of the urchin size, which is well below the range of feed protein contents (9–50%) used in previous studies. The analyses on urchins in experiment I estimated the protein requirement for gonad production of medium and large urchins to be 13% and 15%, respectively, which was lower than that previously reported (>20%). These results indicate that previous studies overestimated the protein requirement owing to protein leaching during the immersion of feed in seawater. Our findings indicate that protein content in sea urchin feed diets can be considerably reduced irrespective of their cultivation stage from seed to market size.

Effects of Marine Microalgae on the Developmental Growth of the Sea Urchin Larviculture Anthocidaris crassipina

The sea urchin is a very important aquatic economic organism in many countries and has high food value. However, it has recently been heavily fished, and it would be of great importance to the sustainable development of coral reefs to develop large-scale aquaculture of sea urchins. Sea urchins are prone to death during larval development. Therefore, in this study, three kinds of microalgae were used as the initial food for sea urchins to evaluate whether different kinds of microalgae can improve their survival and growth rates. Chaetoceros muelleri (C), Isochrysis galbana tml (I), and Dunaliella salina (D) were fed to A. crassipina at concentrations of 5000, 10,000, 20,000, and 30,000 cell mL−1. A fasted group was used as control (N). The final body length, final body width, final stomach length, rudiment length, survival rate and morphology were measured to evaluate development and growth. The results showed that feeding with C. muelleri resulted in better growth and survival. After 9 days of feeding with C(20,000 cells mL−1), the rudiment length reached 203.33 ± 12.47 µm. The onset of metamorphosis was observed 12 days post-feeding. The survival rate after feeding C was also significantly higher than that after feeding I and D. In summary, when sea urchins are breeding, it is recommended to choose C(20,000 cells mL−1) or C(30,000 cells mL−1) as the initial feed for larvae to increase the growth and survival of sea urchin seedlings.

Ethics and Welfare in invertebrates: a stepping-stone to research and animal production

Introduction: Even though only a few species are considered to be dangerous, pests or vectors, the majority of invertebrates produce a feeling of aversion in humans. This has contributed to the delay in the development of ethical considerations as regards this group in contrast with vertebrates, with the exception of cephalopods. &#x0D; Objective: In the present study, we provide an overview of the current situation on animal ethics and welfare in order to contribute to the development of a framework for ensuring invertebrate welfare. &#x0D; Methods: Today, animal welfare is multidisciplinary in nature to a very high degree as it includes ethology, physiology, pathology, biochemistry, genetics, immunology, nutrition, cognitive-neural, veterinary medicine, and ethics. Animal welfare is a complex concept, difficult to achieve successfully from one perspective. &#x0D; Results: As a consequence, we propose to include the five domains (nutrition, environment, health, behaviour and mental state) along with the three conceptions (basic health and functioning, affective state and natural living), as well as the 5R Principle (Replace, Reduction, Refinement, Respect and Responsibility) in seeking to achieve a comprehensive welfare state. &#x0D; Conclusions: We consider that in both research and animal production, the individual and collective ethical concerns coexist and, in fact, the main moral concern to account for is the collective one and that, within that collective view, the individual moral concern should be applied with responsibility and respect for the individual. Finally, we propose a practical example of invertebrate welfare production in sea urchin aquaculture with the aim of including animal production of invertebrates in this important discussion.

Scale-Up of an Aquaculture Plant for Reproduction and Conservation of the Sea Urchin Paracentrotus lividus: Development of Post-Larval Feeds

Paracentrotus lividus gonads, often referred to as “roe” or “uni” for gastronomical purposes, are among the most appreciated seafood delicacies in the Mediterranean area and worldwide. However, the increasing demand for human consumption has caused a growing pressure on its wild stocks, prompting the need to develop efficient aquaculture systems for its production. The set-up of effective feeds for various life stages and optimal procedures for breeding post-larvae and adult sea urchins still need to be improved. Here, for the first time, we aim at developing artificial feeds for the post-larvae of P. lividus because a critical step to improve our productive skills is post-larval growth. We tested various natural and prepared components to speed up the growth and enhance the survival rates of post-larvae, while taking into account the abiotic and biotic factors influencing the culture conditions in three replicate sets of tanks, characterized by different volumes. We tested formulated feeds and compared them with the effect of fresh foods in the frame of canonical culture practices. Our results indicated the efficiency of a feed composed of spirulina and Ulva rigida. Statistical analyses demonstrated the positive impact of this diet on the growth of post-larvae, behavior and survival rates. In addition, we demonstrated the efficacy of prepared feeds in the sea urchin aquaculture system, because they facilitated manipulation and control of the culture procedures for the satisfactory growth of P. lividus post-larvae.

The effect of a formulated feed on the body growth and gonads quality of purple sea urchin (Paracentrotus lividus) aquaculture produced

Sea urchin gonads are a prized gourmet product in many areas of the globe, and wild populations are threatened by increasing demand, making this species a very desirable product in aquaculture. Due to the unique needs of each stage of the life cycle, a viable food protocol that seeks to satisfy each stage while optimizing production profitability is required. The objective of this work was to test a formulated feed for sea urchins, through the analysis of somatic growth, gonad development and their fatty acid profile. These results were compared with sea urchins fed natural food (Ulva spp.) At the end of the trial Paracentrotus lividus juveniles fed inert diet had higher total wet weight gain, total specific growth rate, and gonadosomatic index than those fed with macroalgae. However, histological observations did not reveal differences in the maturation state of the gonads. In comparison to sea urchins fed fresh Ulva spp., inert diet showed higher total wet weight gain and higher total specific growth rate. Fatty acid contents of the gonads of each treatment were found to be similar. The DHA levels in the gonads of sea-urchins fed the formulated feed were significantly higher. It was possible to record the biosynthesis activity of some fatty acids such as 20:4 ω 6, 16:4 ω 3, and 20:3 ω 3. It was found that the presence of some essential fatty acids, such as DHA and EPA, in the gonads is only dependent on the food profile. The addition of a DHA-rich ingredient in the formulated feed may have been preponderant in the constitution and development of the sea-urchins’ gonads.

Comparative Lipidome and Transcriptome Provide Novel Insight Into Polyunsaturated Fatty Acids Metabolism of the Sea Urchin

The sea urchin Strongylocentrotus intermedius is one of the most economically important echinoids harvested from northeast Pacific Ocean coastal waters. The gonads of sea urchins have high nutritional value and are primarily a candidate source of polyunsaturated fatty acids (PUFA). PUFAs are essential for human health, and the biological synthesis and industry production of PUFA have attracted more and more attention from the scientific community. Moreover, PUFAs are important necessary nutrients that determine not only the nutritional value of sea urchins but guarantee their normal growth and reproduction. In this study, we divided 178 sea urchins into three groups (high, medium, and low concentration PUFA groups) according to the concentration of PUFAs, and conducted integrative lipidomics and transcriptomics analyses of different PUFA abundances of S. intermedius to determine the critical genes related to PUFA metabolism in sea urchin gonads. Illumina sequencing generated 894,295,712 clean reads (133.28 Gb) in 18 cDNA libraries. Among all of the unigenes, nine up- and seven down-regulated unigenes were found in a comparison of the “high vs low” concentration PUFA groups of gonads. Interestingly, we found that tudor domain-containing protein 3 (TDRD3) was up-regulated in the high concentration PUFA group, and this gene was significantly related to eicosapentaenoic acid (EPA) in the correlation analysis (p&amp;lt;0.05), and may be used as a candidate marker for EPA biosynthesis and metabolism in the sea urchin. The lipidome and transcriptome information will provide a basic resource for further studies designed to elucidate the molecular mechanism of PUFA metabolism in marine invertebrates, and act as a valuable resource for the practical applications and regulation of the sea urchin aquaculture industry in the future.

Effects of water temperature, age of feces, light intensity and shelter on the consumption of sea urchin feces by the sea cucumber Apostichopus japonicus

The Integrated Multi-Trophic Aquaculture (IMTA) of sea cucumbers and sea urchins has high commercial values. The consumption of sea urchin feces by sea cucumbers is important but largely unknown. The present study aims to evaluate and subsequently improve the fecal consumption in sea cucumbers. Sea cucumbers ingested the feces of sea urchins at both 15 °C and 5 °C, suggesting that the feces of sea urchins has potential to be an appropriate diet for the aquaculture of A. japonicus. Because feces has a complex process after the egestion, the age and temperature significantly affected the fecal consumption by sea cucumbers. The optimal ageing time after egestion was 0–48 h at 15 °C, 0–72 h at 5 °C, respectively. Thus, we recommend aqua-farmers feed A. japonicus with feces at the optimal ageing hours and remove the feces in time. Further, light intensity significantly affected the fecal consumption by A. japonicus. Sea cucumbers had significantly more fecal consumption in low light intensity than that in high light intensity at both 5 and 15 °C. Further, sea cucumbers fed significantly more in low light intensity with shelters than those in low light intensity without shelter, suggesting that shelter provides extra benefits for the fecal consumption by sea cucumbers besides the low light intensity. In addition, significant feeding benefits were found in both low light intensity and shelter at low temperatures. This may solve the problem that sea cucumbers cease feeding at 5 °C in winter. Organizing IMTA in sheltered environment and low light intensity can improve fecal consumption at both 15 °C and 5 °C. The present study provides valuable information in evaluating and improving consumption of sea urchin feces by A. japonicus in the IMTA of sea cucumbers and sea urchins.

Ⅱ-2. Suppressing maturation in sea urchin aquaculture: potential benefits and methods

Ⅱ-2. Suppressing maturation in sea urchin aquaculture: potential benefits and methods

Blue Growth: Sea Urchin Sustainable Aquaculture, Innovative Approaches

Introduction: “Blue Economy” refers to ocean-based economies with a sustainable approach. It focuses in smaller carbon footprints and efficiency, principles that can be applied to aquaculture. However, it has been difficult to develop successful blue economy projects in sea urchin aquaculture. Objective: To compare URCHINOMICS (Norway) and ARBACIA (Argentina), two aquaculture projects with different business models. Methods: We used publicly available information to compare both companies on the basis of their value proposition and tensions (e.g. cultural, social economic and technological). Results: To be successful, sea urchin aquaculture requires development of appropriate technology, open innovation and cooperation of people with different academic, business and organizational backgrounds. Conclusion: The ultimate success of these and similar companies will depend on free interaction of experts from multiple fields and on technological innovation.

Stocking density and rearing environment affect external condition, gonad quantity and gonad grade in onshore sea urchin roe enhancement aquaculture

Finding the ideal density to optimise growth, health and welfare of aquaculture species reared in cage or tank environments allows farmers to produce the best quality product per unit area. Appropriate stocking densities are well known for most major aquaculture species, but limited information exists for the developing sea urchin aquaculture industry. The temperate purple sea urchin Heliocidaris erythrogramma is a prime candidate for aquaculture, yet how stocking density and/or the rearing environment influence urchin health and roe production remain unknown. Here, we tested whether stocking density (low vs. high) and rearing environment (individual vs. group) influences urchin external condition, gonad index (GI) and roe grade in H. erythrogramma after 12-weeks of roe enhancement during autumn-winter (April–June) and winter-spring (July–September) periods. Across rearing environments, high density reduced the proportion of urchins with healthy external condition by 26–30% during autumn-winter and 7–20% in winter-spring compared to low density. During the autumn-winter period, while higher density resulted in lower GIs in the group reared treatments, higher density did not affect the GI of individually reared urchins. Rearing environment affected gonad grade in the autumn-winter period, with a higher proportion of quality (B-grade) roe produced in individually reared treatments compared to group reared treatments. Our results highlight the importance of stocking density and rearing environment for onshore urchin roe enhancement. Maximising production will require a trade-off between investing in greater infrastructure cost to individually rear urchins at high density to ensure higher GIs versus investing in less expensive infrastructure, but group rearing urchins at lower densities to ensure high GIs after enhancement.

Ready to harvest? Spine colour predicts gonad index and gonad colour rating of a commercially important sea urchin

An important problem limiting productivity and profitability of sea urchin aquaculture is the inability of producers to predetermine if sea urchins are ready for harvest. One way to overcome the 10–100% of lost production due to inopportune harvest times is to use external morphological characteristics to determine harvest readiness. To determine whether spine colour may be a useful indicator of harvest readiness, we tested whether there are relationships between spine colour and the size and colour of gonads of the commercially important sea urchin Tripneustes gratilla. Adult T. gratilla were grown in all combinations of three densities and three seawater exchange rates, simulating a range of environmental conditions occurring in culture systems. After six weeks, we measured the size and colour of gonads using standard protocols, quantified spine colour using colour rating and RGB (red, green, blue) intensity, and tested for relationships among these variables using linear models. The models identified significant positive relationships between spine colour predictors and gonad index and gonad colour rating. Our models indicated higher gonad indices were associated with brighter coloured spines, whilst gonads with the highest colour ratings were associated with stronger orange or red coloured spines. Patterns in spine colour identified by our models may reflect variation in colour producing pigments, carotenoids and naphthoquinones, in the epithelium. It is not clear why colour pigments in spines may depend on the colour and size of gonads, but it may be that healthy sea urchins that can grow large gonads also have sufficient energy to obtain and store colour pigments. Alternatively, colour pigments may provide health benefits that facilitate greater gonad size. Overall, our findings suggest that spine colour may be a suitable proxy for determining the harvest readiness of T. gratilla and possibly other sea urchins, but improvement in the reliability of our models and full automation of colour assessments are required before this novel technique can be implemented at commercial scales.