Optimizing Prepared Feed Ration for Gonad Production of the Green Sea Urchin Strongylocentrotus droebachiensis

Adult green sea urchins Strongylocentrotus droebachiensis were fed three different quantities (0.25, 0.50, 1.00% body weight/d) of a prepared feed during a 12‐wk experiment to determine the effect of food ration on gonad quantity and quality. A diet of kelp, Laminaria longicruris and/or L. digitata, fed at satiation (3% body weight/d) and urchins taken from the wild at the beginning and end of the experiment served as controls. Urchins fed prepared feed or kelp increased their percent gonad yield significantly over the experimental period. Affer 12 wk, individuals fed the prepared diet at 0.50 or 1.00% body weighffd had significantly higher percent gonad yields (mean ± SEM: 23.5 ± 0.6% and 23.4 ± 0.7%, respectively) than urchins fed at 0.25% body weight/d (18.0 ± 1.0%) or control animals given kelp (18.3 ± 0.8%). There was no significant difference in gonad yield between the 0.50 and 1.00% feeding levels. All feeding treatments had significantly higher percent gonad yields than urchins sampled from the wild at the end of the experiment that had recently spawned (2.8 ± 0.5%). There was no significant difference in gonad taste among urchins fed the prepared diet at 0.25% body weight/d, those given kelp, or those collected from the wild at the end of the experiment (good to very good ratings), but all of these treatments had significantly better tasting gonads than urchins given the prepared feed at 0.50 or 1.00% body weight/d (satisfactory ratings). Gonad taste rating of urchins fed a prepared diet was dependent on ration with greater feed amounts leading to worse tasting gonads (linear regression: r²= 0.68, P < 0.01). Gonad color, texture, and firmness did not differ significantly among any of the feed ration treatments or kelp control. Results suggest that the best ration for prepared feed would be 0.50% body weightld since this would optimize gonad yield while minimizing feed costs. Further research on prepared feeds is required to optimize both gonad color and taste.     

A comparison of the effect of urchin size and diet on gonad yield and quality in the sea urchin <Emphasis Type="Italic">Evechinus chloroticus</Emphasis> Valenciennes

We compared the gonad-enhancing effects of two diets (NIWA and NIFA diets) in two size classes of sea urchins (Evechinus chloroticus): small and large urchins with a test diameter of 75.6 ± 1.2 mm and 93.8 ± 0.5 mm, weighing 174.8 ± 7.9 g and 315 ± 5.6 g, respectively. After eight weeks being fed prepared diets, urchin gonad index (GI) had significantly surpassed that of the initial and final samples of wild urchins. Urchins in the NIWA/small treatment had a larger GI than the NIFA/small and NIFA/large treatments. The NIWA/large treatment had a larger GI than the NIFA/large treatment. The overall percentage increase in GI for the NIWA/small, NIWA/large, NIFA/small and NIFA/large treatments were 183%, 135%, 132% and 85%, respectively. In terms of gonad colour (CIELAB), there were no significant differences in gonad redness (a*) or yellowness (b*) between experimental treatments, but there was a significant difference in gonad lightness (L*) with small urchins fed both diets having lighter-coloured gonads than the large urchins fed both diets. Sensory assessment of gonads revealed that gonads from small urchins fed both diets were rated as being of better colouration and more uniform in colour than gonads from large urchins. Gonads of urchins fed the NIFA diet were rated as being less bitter and of better overall taste than gonads from urchins fed the NIWA diet. This study shows that feeding prepared diets to E. chloroticus can significantly increase gonad yield but that different diets can affect the magnitude of GI increase and the taste of gonads, and that smaller urchins appear more suitable for gonad enhancement.     

A comparison of three land-based containment systems for use in culturing green sea urchins, Strongylocentrotus droebachiensis (Müller) (Echinodermata: Echinoidea)

Worldwide, most sea‐urchin populations are in decline. Future market demands will likely be met through aquaculture, which may consist of gonad enhancement of wild‐caught sea urchins. In this context, we examined three land‐based containment systems for suitability in maintaining commercial‐size green sea urchins (Strongylocentrotus droebachiensis). Mortality rate, gonad quantity, gonad quality (colour, brightness, firmness, texture) and cleaning efficiency associated with each containment system were the criteria for comparing the effectiveness of the systems (large raceways, small raceways and washtub tanks). After 6 weeks, urchins maintained in large raceways displayed significantly higher mortality rates than urchins maintained in either the small raceways or washtub tanks (mean±SD: 24.3±10.4%, 8.0±3.5% and 4.3±1.5% respectively). Significant differences in cleaning time were detected among the three systems with washtub tanks requiring significantly more cleaning time (0.11±0.02 min urchin^?1) than the other two systems and large raceways requiring significantly less cleaning time (0.06±0.02 min urchin^?1) than the other two systems. No significant differences in gonad characteristics were detected among the three containment systems. Because of the higher mortality rate in the large raceways and the increased cleaning time required for the washtub tanks, the small raceways were considered to be the best of the three systems tested.     

The relationship between feed intake and gonad growth of single and stocked green sea urchin (Strongylocentrotus droebachiensis) in a raceway culture

This study provides a robust relationship between feed intake (FI), gonad growth (GG), and feed conversion ratio (FCR) of cultured adult green sea urchin Strongylocentrotus droebachiensis. Sea urchins (test diameter: ∼ 54 mm and live weight: ∼ 70 g) were collected in the wild and cultured either individually or subjected to one of three stocking densities, i.e. low 2.5 (N = 36), medium 3.7 (N = 54), or high 7.3 (N = 108) kg animal per m². Animals were fed a prepared diet in excess for 56 days at 6.5-4.5 °C. The gonad index (GI) more than doubled during the 56 day trial. The final mean values of GI (17-18%), FI (0.3-0.4 g feed per animal per day), and FCR (∼ 3 g feed per g increase in gonad weight) were statistically similar between individual and stocked animals. Based on data from the individually cultured sea urchins, the relationship between daily FI (g feed per animal) and GG (g gonad increase per animal) could be described by the equation: GG = 0.619FI − 0.097 (R² = 0.533, P < 0.001). In conclusion, marketable sizes of green sea urchin perform well in raceways at densities of 7-8 kg animal per m² without adverse effects on FI, GG, and FCR.     

Cu2+对中间球海胆生长、免疫及性腺发育的影响

为探讨铜离子(Cu2+)对中间球海胆生长和性腺发育的影响及调控机制,在室内水槽(200 L)中进行为期60 d的浸泡实验。实验设置测试组(0.02 mg/L Cu2+)和对照组(自然海水),每个处理设置3个重复,每个水槽养殖20只海胆(13.58±0.79)g。实验中期和末期分别测定海胆增重率(WGR)、性腺指数(GI)、抗氧化酶活性和主要卵黄蛋白基因(MYP)表达量。结果显示,30 d时,测试组的WGR和GI与对照组差异不显著,而60 d时测试组的WGR和GI显著低于对照组;60 d时,测试组海胆体腔液中过氧化氢酶(CAT)和谷胱甘肽巯基转移酶(GST)活性均显著低于30 d时的对应值,而丙二醛(MDA)含量较30 d时有所升高;60 d时,测试组抗氧化能力总体高于对照组,其中体腔液中CAT活性显著高于对照组。2次取样中,测试组性腺中MYP基因的表达量均显著低于对照组,而测试组消化道中MYP基因的表达量却显著高于对照组。60 d时,测试组海胆体腔细胞中总蛋白含量显著高于对照组,而体腔液上清液中总蛋白含量在测试组和对照组之间差异不显著。研究表明,铜离子能够引起氧化应激,降低海胆的增重率和性腺指数,这可能是通过抑制性腺MYP表达量及阻碍MYP从消化道向性腺正常转运所致。     

The effect of fresh seaweed and a formulated diet supplemented with seaweed on the growth and gonad quality of the collector sea urchin,Tripneustes gratilla,under farm conditions

This gonad enhancement study investigates the effect of different fresh and formulated feeds and feeding regimes on the growth and gonad quality of wild‐collected adult sea urchin, Tripneustes gratilla, under farm conditions for over 18 weeks. In the first 12 weeks (phase 1), urchins were fed fresh Ulva rigida (U); a 50:50 mixture of fresh U. rigida and Gracilaria gracilis (UG); fresh G. gracilis (G) and a formulated diet 20U (containing 20% U. rigida), and in the final 6 weeks (phase 2) of the study, diet was changed to a formulated feed (20U diet). By the end of phase 1, urchins fed the 20U diet produced gonads (50.72 ± 5.4 g) that were significantly heavier (p < .001) than the gonads of urchins fed the fresh seaweed diets (U, UG & G). By the end of phase 2, gonad weight of urchins in treatment groups UG‐20U and G‐20U were similar to those fed the 20U‐20U diet. Gonad colour of urchins in the G‐20U treatment became significantly lighter (ANOVA, p = .029) and poorer quality, compared with urchins in the U‐20U group. This gonad enhancement study, conducted on wild‐collected adult T. gratilla, has shown that a formulated feed (20U diet) can enhance gonad growth and produce commercially acceptable gonads. This farm‐based study supports previous findings from aquarium‐based studies by our group and indicates that short‐term sea urchin gonad enhancement can be carried out under farm conditions in South Africa.     

Formulated Feed Supports Weight Gain and Survivorship in Juvenile Sea Urchins Lytechinus variegatus

In adult sea urchins, formulated feeds can support both weight gain and gonad production; however, studies demonstrating the effects of formulated feeds on juvenile sea urchin growth are limited. In this study, juvenile sea urchins (test diameter: 3.20–7.33 mm, N = 12 per treatment) were reared individually in artificial seawater and fed with one of four experimental feeds: (1) mixed‐taxa algal biofilm (MTAB), (2) freeze‐dried MTAB, (3) a commercial, small‐mammal feed (Friskies^® cat treats), or (4) a semipurified feed formulated for sea urchins. The MTAB and sea urchin feed supported weight gain and survival throughout the study; however, those individuals fed with the sea urchin feed exhibited a short lag period at the onset of feeding. This short lag period may be, in part, because of an initial lack of attraction of the urchins to the formulated feed. Furthermore, we hypothesize that gut physiology or gut flora must acclimatize to a new diet (all sea urchins were reared initially on the MTAB diet). The freeze‐dried MTAB and mammal feed did not support substantial weight gain. This study suggests that sea urchin juveniles as small as 3–4 mm can utilize formulated feeds for growth.     

Long-term effects of stocking density on somatic growth,gonad index and survival of the juvenile sea urchin, <Emphasis Type="Italic">Strongylocentrotus droebachiensis</Emphasis>

Juvenile Strongylocentrotus droebachiensis (average wet weight = 4.0 g) were held at three initial stocking densities (15, 30 and 60 animals per tray, which equates to 0.25, 0.5 and 1 kg sea urchins/m² surface area, respectively) under constant light and temperature conditions (LD 24:0 and 8.8°C) for 380 days. The somatic growth and survival of the urchins were monitored during this period, and the gonad index (GI) was measured at the conclusion of the experiment. The sea urchins in the two lowest stocking density groups had 100% survival after 380 days in contrast to the highest stocking density group, which only had 67% survival at the conclusion of the experiment. Somatic growth was significantly higher in the lowest density group than in the medium density group, and this in turn was significantly higher than in the high-density group. The injury occurrence was highest in the high-density group (20%), lower in the medium group (7%), and there were no injuries observed (0%) in the low density groups. There were no significant differences in GI between the groups at the end of the experiment. In conclusion, the present study showed that stocking density has significant effects on somatic growth and survival of juvenile green sea urchin, S. droebachiensis and should be taken into consideration when designing sea urchin holding systems.     

Effects of dietary carbohydrate on weight gain and gonad production in small sea urchins,Lytechinus variegatus

In experiment 1, juvenile sea urchins (n = 80, 0.088 ± 0.001 g wet weight and 5.72 ± 0.04 mm diameter) were held individually and fed ad libitum one of three semi‐purified formulated diets (n = 16 individuals treatment^?1). In the diets, protein was held constant (310 g kg^?1 dry, as fed) and carbohydrate level varied (190, 260, or 380 g kg^?1 dry, as fed). Wet weights were measured every 2 weeks. Total wet weight gain was inversely proportional to dietary carbohydrate level and energy content of the respective diet. In experiment 2, sea urchins (5.60 ± 0.48 g wet weight, n = 40) fed 190 g kg^?1 carbohydrate consumed significantly more dry feed than those fed 260 g kg^?1, but not more than those fed 380 g kg^?1 carbohydrate. Based on differential feed intake rates, sea urchins that consumed more feed also consumed higher levels of protein and had the highest weight gain. Consequently, protein content and/or protein: energy ratio may be important in determining feed utilization and growth among sea urchins in this study. The average digestible energy intake was approximately 70 kcal kg^?1 body weight day^?1, suggesting daily caloric intake of juvenile Lytechinus variegatus is lower than in shrimp and fish.     

Ingestion, Absorption, and Gonad Production of Adult Strongylocentrotus franciscanus Fed Different Rations of a Prepared Diet

Abstract.— Feed costs are a major portion of aqua-culture operations. Accurate estimates of daily ration are vital to prevent overfeeding which results in wasted feed. poor water quality, underfeeding, and reduced growth. Understanding the relationship of ingestion rate and absorption efficiency of Strongylocentrotus franciscanus should improve the cost effectiveness of aquaculture of this candidate species. Adult S. franciscanus were collected from a subtidal area devoid of algae and fed two rations of an extruded diet for 62 d. Mean test diameter and whole weight of an initial sample were 91 ± 2 mm and 295 ± 18.4 g (mean ± SEM; N = 16). The two rations used were l-g dry feed/d or 3 g/d. An unfed control group was also maintained. Eight urchins per treatment showed significant differences in food ingestion rate, total organic absorption, gonad index, gut index, and moisture content of the gonad (P < 0.001). Food intake was greatest in the high ration treatment, while total organic absorption was greatest in the low ration treatment. The gonad index of S. franciscanus in the high food ration was significantly greater than the initial gonad index and was also greater than the index of animals in the low ration and unfed treatments. The gonad index of animals in the low food ration treatment was significantly greater than the index of the initial sample and the index of animals in the unfed treatment. The gut index of urchins in the high food ration treatment was significantly greater than initially and was also greater than the gut index for animals in the low ration and unfed treatments. The gut index for urchins in the unfed treatment was significantly less than the initial index. The moisture content of the gonad of urchins fed the prepared diet was significantly greater than the gonad moisture content of the initial sample or unfed group. Test diameter. whole animal weight, and gonad production efficiency (increase in g dry gonad weight/g dry feed intake) were not significantly different (P > 0.200). Histological examination of the gonads showed S. franciscanus in the two ration treatments developed from the spent to the growing or premature stage while the unfed controls lost nutritive tissue and contained only relict gametes or remained in the spent condition. The results suggest S. franciscanus from food-limited environments can be fed appropriate rations to control gonad production.     

Effects of biofilms as the main and as a supplementary food on the survival,somatic growth and gonad enhancement of sea urchin Strongylocentrotus intermedius

Cultured sea urchins of similar size (mean ± SE = 4.33 ± 0.48 g in body weight) were fed biofilms only, kelp (Laminaria japonica)+biofilms (biofilms as supplementary food) and a control diet of kelp only for 7 months in the laboratory. The somatic growth and the survival rate of the sea urchins were measured monthly, and the gonad wet weight and gonad color difference were determined at the end of the experiment. The results show that diet did not significantly affect survival rate (P > 0.05), but had highly significant effects on somatic growth from the first month to the end of the experiment (P < 0.01). Sea urchins fed biofilms only showed negligible or even negative somatic growth at the end of the experiment. Sea urchins on the kelp+biofilms grazed biofilms and consumed kelp during the experiment, and showed sustained greater increase in body weight than those of fed kelp only after the fourth month (P < 0.05). The biofilms may have supplied micronutrients. At the end of the experiment, gonad production of sea urchins fed biofilms was too little (0.11 ± 0.09 g) to identify sex and measure color. Gonad wet weights of males and females and gonad color fed kelp+biofilms did not differ significantly from those of fed kelp only (P > 0.05). However, sea urchins fed kelp+biofilms were more uniform in gonad color than those fed kelp only (P < 0.01), indicating biofilms supplementation could reduce the percentage of low-grade roe. This study therefore reveals the potential of biofilms as a supplementary food in the culture of sea urchins.     

Long-term effects of stocking density on survival,growth performance and marketable production of the sea urchin <Emphasis Type="Italic">Strongylocentrotus intermedius</Emphasis>

Sea urchins were stocked at a density of 15 (D15), 30 (D30), 45 (D45) and 60 (D60) urchins/cage (0.3 m long × 0.2 m wide × 0.4 m high) in a laboratory culture environment for 16 months. The wet body weight (BW) and test diameter growth were monitored at 2-month intervals during the experiment. At the conclusion of the experiment, the surviving sea urchins were counted and the gonad wet weight (GW) and gonad color were measured. Specific growth rate (SGR) of body weight, survival rate (SR), gonad index (GI), gonad color difference (ΔE ₀₀), coefficients of variation (CV) of BW, GW, GI and ΔE ₀₀, total biomass yield (TY) and total gonad yield (TGY) per cage were calculated. Two marketable yield variables, graded according to gonad index, i.e., marketable biomass yield (MY) and marketable gonad yield (MGY), were also calculated. Coefficient of variation of final body weight (FW) and final test diameter (FTD) of sea urchins increased as the stocking density increased, indicating the existence of adverse social interactions. These adverse social interactions detrimentally affected FW, FTD, SGR, GW and GI (P < 0.01). Although SR decreased with the increasing densities, no statistical significant difference was detected. Sea urchins at D15 had the lowest gonad color difference (ΔE ₀₀) (P < 0.05). However, statistically equal CV of ΔE ₀₀ indicates this density effect was not a result of adverse social interactions. TY and TGY increased with increased density and can be described by the following equations: TY = 84.18X ^0.64, R ² = 0.999 and TGY = 24.16X ^0.38, R ² = 0.979. However, the MY and MGY were not significantly different among stocking densities. The results of this study demonstrate that in intensive culture S. intermedius at low stocking density can achieve high growth rate, gonad index and desirable color without decreasing the marketable yield. Farmers should choose to culture S. intermedius at low stocking densities.     

Increased gonad growth of the purple sea urchin (Strongylocentrotus purpuratus) fed the giant kelp (Macrocystis pyrifera) and the sea lettuce (Ulva lactuca) enriched with nutrients

Adult (Strongylocentrotus purpuratus) purple sea urchins were fed giant kelp (Macrocystis pyrifera) and sea lettuce (Ulva lactuca) macroalgae that were unenriched and enriched with nutrients. Urchins were fed over 10 weeks (5% body weight per day) under laboratory conditions to determine the effect of macroalgae species and treatment (enriched and unenriched) on growth, gonad index and gonad quality. Significant differences were observed when urchins were fed enriched Macrocystis pyrifera (MPE). Gonad weight increased from 0.7 ± 0.1 g (mean ± SD) to 5.9 ± 1 g, and gonad index increase from 3.5 ± 1.5% to 14.9 ± 2.3% over 10 weeks. Significant differences were also noted in gonad quality, and gonad colour and firmness were better in urchins that were fed unenriched M. pyrifera (MPUE) and MPE – whereas texture did not differ between M. pyrifera treatments and unenriched U. lactuca (ULUE). With regard to taste, gonads were sweeter in MPE‐fed individuals. Enriched U. lactuca (ULE) failed to grow gonads significantly; as a result, their quality was unacceptable for the market. These results suggest that S. purpuratus experience increased gonad production and quality in short periods when fed nutrient‐enriched M. pyrifera.     

The effects of tank system,water velocity and water movement on survival,somatic and gonad growth of juvenile and adult green sea urchin,Strongylocentrotus droebachiensis

The effects of water velocity and tipping frequency (water movement) on survival, somatic and gonad growth of juvenile and adult green sea urchin, Strongylocentrotus droebachiensis were investigated. Juvenile and adult urchins were held in ‘laminar’ or ‘tipper’ tanks. Both were supplied with three inlet water flows (1.5, 3.0 and 7.5 L min^?1) which converted to water velocities of 0.28, 0.57 and 1.43 cm s^?1 in the ‘laminar’ tanks and tipping frequencies of 30, 10 and 5 s in the ‘tipper’ tanks. Juvenile sea urchins had significantly lower mortality and greater somatic growth when held in ‘laminar’ flow tanks compared with ‘tipper’ tanks. The varying water velocities tested in the ‘laminar’ flow treatment had no effect on the growth of juvenile sea urchins. The juvenile sea urchins in the ‘tipping’ treatment held at high tipping frequency had significantly slower growth than those in the medium and low tipping frequency treatments. There were no differences in mortality or gonad growth in the adult sea urchins regardless of treatment. The ‘laminar’ flow tanks retained significantly more organic material compared with the ‘tipper’ tanks. The authors discuss the effects of water velocity and tipping frequencies in system design for aquaculture of sea urchins.     

Effect of Feed Protein and Carbohydrate Levels on Feed Intake,Growth, and Gonad Production of the Sea Urchin,Lytechinus variegatus

In this study, we evaluated protein and carbohydrate levels in cold‐extruded dry diets. Sea urchins (12.6 ± 0.12 SE g wet weight, 29.5 ± 0.11 SE mm diameter) were collected from St. Joseph Bay, Florida (30°N, 85.5°W), and transported to the Texas Agrilife Research Mariculture Laboratory in Port Aransas, Texas. Urchins were held individually in replicated enclosures within a recirculating seawater system (32 ± 2 ppt and 22 ± 2 C). Urchins (n = 16urchins) were fed diets that differed in protein : carbohydrate levels (31:33%, 25:39%, 21:44%, and 17:47% dry weight) for 12‐wk. Survival was 100% in all diet treatments. Urchins fed the 31:33% protein : carbohydrate diet consumed less feed, more dry protein, less dry carbohydrate, less energy, and had lower feed conversion ratios than urchins fed other diets. Urchins fed the 31:33% protein : carbohydrate diet had larger test diameters, total wet weights, production efficiencies, and gonad production efficiencies than urchins in the other diets. Weight gain varied directly and significantly with protein intake. Sufficient energy was available for maximum weight gain as protein was spared. Growth rates and production efficiencies for the urchins in this study were higher than in previous feeding studies with adult Lytechinus variegatus.     

Assessment of magnesium chloride as an anaesthetic for adult sea urchins (Paracentrotus lividus): incidence on mortality and spawning

During this study different concentrations of magnesium chloride (MgCl₂) were tested on adult wild‐caught sea urchins (Paracentrotus lividus) immediately after their collection in the field in order to assess whether MgCl₂ can act as an anaesthetic during their transport and prevent unplanned spawning. Such accidental spawning is a stress response associated with transport of this species. The mortality and gonadal indices were recorded after a 1‐h submersion in different strength solutions of MgCl₂ (5, 20, 40, 80 and 100 mmol L⁻¹ MgCl₂), followed by 5 h of dry transport under two different temperatures (19 and 25 °C). The effective concentration of MgCl₂ was defined as one that does not induce mortality and gonad mass loss following sea urchin transport and laboratory conditioning. Treatment of sea urchins with 5 mmol L⁻¹ MgCl₂ prevented mortality and unplanned spawning; however, elevated concentrations of magnesium (40, 80 and 100 mM) were toxic to sea urchins, inducing a massive mortality and gonad mass decrease during the acclimatization period, essentially when sea urchins were transported under an elevated temperature (25 °C). It is concluded that MgCl₂ is a suitable non‐toxic anaesthetic, easily available for adult sea urchins (P. lividus) when it is used at its optimal anaesthetizing concentration.     

Effects of Hyperoxic Conditions on Growth Performance in Juvenile and Adult Green Sea Urchin,Strongylocentrotus droebachiensis

The effects of hyperoxic conditions on survival, gonad growth, feed intake, and food conversion of adult and somatic growth and survival of juvenile green sea urchin, Strongylocentrotus droebachiensis, were examined. Juvenile and adult sea urchins with initial diameters of 11.5 and 75 mm, respectively, were reared in water with constant oxygen saturations of 100 (control), 115 and 130% for 42 d (juvenile) and 51 d (adult sea urchin) at 8 C and 33‰ salinity. During the experiment the gonad indices of the adults tripled from 7.3% (±1.5) to 21.4% (±4.3), 19.4% (±4.7), and 22.0% (±4.4) for the groups kept at 100, 115, and 130% oxygen saturation, respectively. At the end of the experiment, the differences in gonadal size among the groups were not significant. Neither were there any significant differences in food intake or food conversion ratio among the groups. Only one animal died during the experiment. The juvenile sea urchin kept at 100, 115, and 130% oxygen saturation doubled their test diameter from initially 11.5 mm (±1.5) to 19.9 mm (±1.4), 21.4 mm (±2.1) and 20.6 mm (1.0), respectively, but there were no significant differences in growth among these groups. There was no mortality during the experiments in these groups. Overall, the findings suggest that juvenile and adult S. droebachiensis are unable to utilize hypersaturation of oxygen to increase somatic or gonad growth, but can be reared at hyperoxygenated water for prolonged periods of time without harmful effects.     

The effects of stocking density on gonad growth, survival and feed intake of adult green sea urchin (Strongylocentrotus droebachiensis)

In this study the effects of different stocking densities on survival, gonad growth and feed intake in adult green sea urchin (Strongylocentrotus droebachiensis) were examined. Two size groups of sea urchins with respective initial mean weight of 45 g (S) and 70 g (L) were used. The experiments were carried out in 755 l plastic tanks divided into chambers by vertical fibreglass lamellae. In the two experiments stocking densities of 6, 12, 14 and 16 kg m^− 2 (Exp I) and 3, 6 and 8 kg m^− 2 (Exp II) were used. Sea urchins reared individually in compartmentalised raceways were used as controls in both experiments. All groups were fed a formulated moist feed ad libitum for 60 days at 8 °C (± 0.5). Mortality was observed in all groups, except for the control group and the lowest density group of large sea urchins (3 kg m^− 2, L). Both mortality and occurrence of injuries increased significantly with increasing stocking density in both experiments and for both size groups. In the highest density groups mortality was 60% (L) and 80% (S). There was a significant increase in gonad index during the experimental period in both experiments. Increased stocking density had a significantly negative effect on gonad growth in both size groups while feed intake was unaffected. The results show that adult S. droebachiensis can maintain high survival rate and high gonad growth at stocking densities up 6 kg m^− 2 in holding facilities of the design used in the present study.     

The value of sea urchin,Lytechinus variegatus,egesta consumed by shrimp,Litopenaeus vannamei

Sea urchins produce high‐energy, membrane‐bound fecal pellets that contain residual nutrients and large quantities of microbiota. These egesta are readily consumed by the shrimp, Litopenaeus vannamei. Egesta of the sea urchin, Lytechinus variegatus, were evaluated as a feed supplement or total replacement for a commercial shrimp diet. Shrimp were stocked at 0.49 g ± 0.06 g initial body weight and housed individually in 2.8‐L tanks in a commercial recirculating zebrafish system. Shrimp were assigned to one of six diets: commercial shrimp feed, reference sea urchin feed, collected dried sea urchin egesta, collected wet sea urchin egesta, half ration of shrimp feed and half collected wet sea urchin egesta, and egesta naturally produced by two sea urchins in polyculture. Equivalent dry matter amounts of each diet were proffered to shrimp in each treatment twice daily, except for those that had complete access to natural egesta excreted by sea urchins in polyculture. Sea urchins were proffered a reference sea urchin feed at 2% body weight daily. After 27 days, shrimp proffered collected dried or wet egesta did not differ significantly in percent weight gain and showed the lowest weight gain. The percent weight gain of shrimp fed the commercial shrimp diet did not differ significantly from that of the shrimp fed half commercial shrimp diet and half egesta. The highest weight gain was recorded for those shrimp that consumed the untouched egesta produced by sea urchins in polyculture. These data suggest that consumed egesta have noteworthy nutritional value and therefore would be beneficial to the culture of extractive species in an integrated multitrophic aquaculture system.     

Effect of different feed formulations on feed efficiency, gonad yield and gonad quality in the purple sea urchin Heliocidaris erythrogramma

The nutritive values of three pelleted prepared diets, based on animal (AP), vegetable (VP) and yeast protein (YP) were studied for the sea urchin Heliocidaris erythrogramma (Val.). Fresh macroalga Ulva australis was used as a natural control diet. Triplicate groups of five animals were fed one of the four diets ad libitum every second day for 85 days. Sea urchins fed pelleted feeds had significantly higher food consumption rates (dry basis) and significantly lower total and protein absorption efficiencies compared with the algal diet. The gonad yield and gonad production efficiency in sea urchins fed the natural diet were significantly higher compared with initial group (gonad yield only) and urchins fed animal and vegetable diets, but did not differ significantly from those of the animals fed the yeast diet. Percent protein and lipid in the gonads were not affected by the dietary source. The taste and smell of gonads were generally better in sea urchins collected from the wild or fed yeast and natural diets than in sea urchins fed animal and vegetable diets. The animal protein diet was the most stable in seawater while the yeast protein diet had the poorest water stability. The results of this study suggest that development of a more stable, single‐cell, protein‐based diet has a potential to promote gonad production of H. erythrogramma.