Christopher M. Pearce

Effect of protein source ratio and protein concentration in prepared diets on gonad yield and quality of the green sea urchin, Strongylocentrotus droebachiensis.

Adult green sea urchins (Strongylocentrotus droebachiensis) were collected from the wild and held in laboratory tanks where they were fed a number of prepared diets or a control of kelp (Laminaria longicruris and/or L. digitata) for a period of 12 weeks. Twelve different prepared diets were formulated in order to examine two experimental factors: (1) protein concentration at three different levels [19%, 24%, and 29% (percent dry weight of all dietary components)] and (2) protein source ratio at four different levels [rockweed meal, wheat meal, corn meal, soybean meal, fish meal in the following four ratios: 0:30:30:25:15, 15:20:20:35:10, 30:10:10:45:5, 45:0:0:55:0, respectively (percent dry weight of all meals)]. Each concentration was present at each source ratio in a completely crossed experimental design. Gonad colour, percent gonad water, and percent gonad yield of experimental urchins were determined approximately every week while gonad texture, firmness, and taste were subjectively evaluated at the end of the experiment. Results were contrasted with those of wild specimens collected from the source population at weeks 0 and 12 of the experiment. After 12 weeks, all prepared diets produced significantly higher percent gonad yields than kelp-fed urchins or wild controls, the best-prepared diet giving a mean weekly increase of 1.3% in percent yield. Percent gonad yield was not significantly affected by protein concentration, but was significantly affected by protein source ratio; the 15:20:20:35:10 diet gave significantly higher yields than the 0:30:30:25:15 or 45:0:0:55:0 diets (30:10:10:45:5 being intermediate). Gonad colour of urchins fed prepared diets was, generally, pale yellow/orange to yellow-brown/orange-brown at the end of the experiment and not significantly different from kelp-fed urchins or wild controls. Gonad colour was not significantly affected by protein source ratio, but was significantly affected by protein concentration; the 19% and 24% levels produced significantly better coloured gonads than the 29% level. At the end of the experiment, gonad texture of urchins fed prepared diets ranged from smooth to very smooth with distinct gonad segment halves while gonad firmness ranged from firm to very firm. Gonad texture and firmness of prepared diet treatments did not differ significantly from kelp-fed urchins or wild controls and neither protein concentration nor protein source ratio significantly affected gonad texture or firmness. At the end of the experiment, gonad taste of urchins fed prepared diets ranged from bitter to sweet with all prepared diets producing significantly worse tasting gonads than the kelp-fed urchins. Gonad taste was not significantly affected by protein source ratio nor protein concentration, but there was a general trend of worsening taste with increasing protein levels. Based on these results, a 19% protein concentration and a 15:20:20:35:10 (rockweed meal/wheat meal/corn meal/soybean meal/fish meal) protein source ratio are recommended for further dietary research.

Effect of binder type and concentration on prepared feed stability and gonad yield and quality of the green sea urchin, Strongylocentrotus droebachiensis

Abstract Adult green sea urchins, collected from the wild, were held in laboratory tanks and fed one of eight prepared feeds—varying solely in the type and concentration of binder used in the diet (i.e. gelatin, guar gum, sodium alginate, or corn starch each being present at 3% or 5% dry weight)—for a period of 12 weeks. Two control treatments, kelp and a commercially available salmon feed, were also included. Gonad colour, percent gonad water, and percent gonad yield of urchins in the 10 feeding treatments were determined approximately every week while gonad texture, firmness, and taste were subjectively evaluated at the end of the experiment. Results were contrasted with those of wild specimens collected from the source population at weeks 0, 4, and 12 of the experiment. Pellet coherence and amount of feed lost were examined in separate feed stability trials. After 12 weeks, all prepared feeds produced significantly higher percent gonad yields than kelp or wild controls. Binder type significantly affected percent gonad yield at week 9, the highest yield being attributed to feeds made with gelatin. By week 12, however, there were no significant differences in percent gonad yield among the different binders and this was attributed to yields reaching a physiological maximum. Binder concentration significantly affected percent gonad yield at the end of the experiment with the higher concentration producing greater yields. While gonad colour was significantly affected by binder type (starch producing better colour than any other binder), all prepared feeds generally produced gonads that were cream or tan in colour. This contrasted with kelp-fed or wild controls that typically had pale yellow or orange gonads. Binder concentration did not significantly affect gonad colour. While the texture of gonads from urchins fed prepared feeds was statistically similar to that of gonads taken from kelp-fed or wild individuals, firmness and taste were significantly poorer. Binder type and concentration did not significantly affect gonad texture, firmness, or taste. Feed stability was significantly affected by binder type (gelatin producing more stable pellets than any other binder), but not concentration. Amount of feed lost from pellets was not significantly affected by binder type or concentration, but this was most probably due to the fact that flow rates in the tanks were not sufficient to wash broken feed out of experimental units. Based on these results, gelatin is the binder recommended for use in further dietary experiments and commercial-scale feed operations.

Role of dissolved and particulate cadmium in the accumulation of cadmium in cultured oysters (Crassostrea gigas)

Pacific oysters (Crassostrea gigas) collected on the coast of British Columbia, Canada have occasionally shown cadmium (Cd) concentrations at or above 2 microg g(-1) (wet weight), which has resulted in the loss of some international markets. This study investigated the source and transfer of Cd to oysters by focusing on the role of dissolved and particulate Cd in seawater. Parameters monitored for 1 year at two oyster farm sites on Vancouver Island included: oyster tissue mass and shell length, Cd in oysters, dissolved Cd, particulate Cd, temperature and salinity. Results show that dissolved Cd was the main source of Cd to the oysters and that Cd was mainly concentrated in the gut tissues. A seasonal trend was observed in Cd in oysters, in which levels were lowest during periods of higher temperatures. Results also indicate that the local oceanographic inputs and sediment diagenesis directly affect dissolved Cd and thereby influence the Cd levels in oysters. Particulate matter was not found to be a source of Cd in oysters, and was actually negatively correlated. This was likely due to the uptake of dissolved Cd by phytoplankton and the effect of phytoplankton on oyster tissue mass.

Fertilization and Embryonic Development in the Basket Cockle, Clinocardium nuttallii

Abstract Sperm motility, fertilization, and embryonic development were investigated in the hermaphroditic basket cockle, Clinocardium nuttallii. Motility of the sperm was more prolonged over a 2-h storage period at 4°C than at 19°C. The sperm-to-egg ratio resulting in the highest fertilization rate was 10,000:1, or an equivalent final sperm concentration of 6 × 105 cells mL−1, using a density of 60 eggs mL−1. However, at least some degree of self-fertilization appeared to be unavoidable during the release of the eggs from the broodstock. The biological zero point, below which embryonic development ceased, was estimated to be 2.8°C to 2.9°C for C. nuttallii.

Growth Rate of the California Sea Cucumber Parastichopus californicus: Measurement Accuracy and Relationships between Size and Weight Metrics

Abstract Management of the fishery for California sea cucumbers Parastichopus californicus in the Pacific Northwest is limited by a lack of natural growth rate estimates. Growth rates of caged juvenile California sea cucumbers (from Departure Bay, British Columbia) consuming a natural diet for 12 months (September 2008–September 2009) were examined. Growth was low between September and March but significantly increased thereafter, appearing to follow seasonal physiological processes, temperature, and natural sedimentation rates. Over the 12-month period, whole wet weight in air (WWA) increased by an average of 164%, immersed whole weight (IWW) increased by 251%, and the size index (SI) increased by 85%. Average standard growth rates were 0.267%/d for WWA, 0.346%/d for IWW, and 0.169%/d for SI. Measurement accuracy, effects of body content, and relationships between size and weight metrics are discussed. These findings are an important addition to the knowledge of California sea cucumber biology and are va...

Broodstock Conditioning in the Basket Cockle, Clinocardium nuttallii

Abstract Factors affecting broodstock conditioning in the hermaphroditic basket cockle, Clinocardium nuttallii, were examined in laboratory experiments. Although a 13-wk experiment conducted at 16°C failed to bring C. nuttallii broodstock into spawning condition under different dietary treatments, initiation of gametogenesis was apparent for those broodstock maintained at 2.5°C. Condition indices were significantly greater when broodstock were fed a combination of Isochrysis galbana (Tahitian strain, T-iso) and Chaetoceros gracilis (CG) or T-iso and Thallasiosira pseudonana (3H) than when fed a combination of Tetraselmis suecica (TS) and 3H or TS and CG, indicating that T-iso may be a better food source than TS for cockle broodstock conditioning.

The Canadian Integrated Multi-Trophic Aquaculture Network (CIMTAN)—A Network for a New Era of Ecosystem Responsible Aquaculture

ABSTRACT The Canadian Integrated Multi-Trophic Aquaculture Network (CIMTAN) is a Natural Sciences and Engineering Research Council strategic network that was initiated in 2010. It was triggered by the fact that aquaculture, though the world fastest growing food production sector, is associated with environmental, economic, and societal issues. Integrated multi-trophic aquaculture (IMTA) offers an innovative solution for the environmental sustainability, economic stability, and societal acceptability of aquaculture by taking an ecosystem-based management approach. IMTA is the farming, in proximity, of aquaculture species from different trophic levels, and with complementary ecosystem functions, so that one species’ excess nutrients are recaptured by the other crops and synergistic interactions among species occur. CIMTAN is providing the interdisciplinary research and development and highly qualified personnel training in the following linked areas: (1) ecological design, ecosystem interactions, and biomit...

Does Method of Kelp (Saccharina latissima) Storage Affect Its Food Value for Promoting Somatic Growth of Juvenile Green Sea Urchins (Strongylocentrotus droebachiensis)

ABSTRACT Harvested for their gonads, sea urchin populations are declining worldwide primarily as a result of overfishing. Consequently, research is now focusing on full life cycle aquaculture of these organisms. If juvenile or adult sea urchins are to be fed macroalgae (a preferred food of echinoids) in commercial-scale operations, suitable methods for storing large amounts of algae will be required. In this study, the effect of various storage methods for the kelp Saccharina latissima on somatic growth of juvenile green sea urchins, Strongylocentrotus droebachiensis, was evaluated. Juvenile S. droebachiensis (initial test diameter, 4.5–10.7 mm) were held in laboratory tanks, supplied with flow-through seawater, and fed ad libitum one of the following S. latissima treatments: (1) frozen long term (>2 mo), (2) frozen short term (1 wk), (3) air-dried, or (4) fresh. Measurements of test diameter and whole wet weight of the sea urchins were taken monthly for 16 mo. Mean (±SE) final sizes in the treatments ranged between 17.7 ± 0.4 mm and 21.7 ± 0.4 mm for test diameter and between 2.9 ± 0.2 g and 4.9 ± 0.2 g for wet weight (sea urchins fed long-term frozen kelp and air-dried kelp, respectively). There were no significant differences in growth rate—for either test diameter or wet weight—among sea urchins fed short-term frozen, air-dried, or fresh kelp, but those individuals fed long-term frozen kelp grew significantly slower than those on any of the other 3 diets. It is unclear, however, whether this difference is the result of the long-term freezing process per se or the result of differences in the biochemical nature of the kelp plants when they were collected for freezing. Because air drying should be relatively cheaper than freezing (in terms of energy cost), and air-dried kelp may be more easily stored and transported than frozen or fresh kelp, air drying is an obvious choice for long-term storage of kelp if it is to be used as a food for juvenile green sea urchins.

The role of phytoplankton in the modulation of dissolved and oyster cadmium concentrations in Deep Bay, British Columbia, Canada.

We previously identified dissolved cadmium (Cd(diss)) as the main source of this metal in cultured Pacific oysters, Crassostrea gigas, in Deep Bay, British Columbia, Canada (Lekhi et al., 2008). Total suspended particulate Cd (Cd(part)) was not found to be a significant source of oyster Cd (Cd(oys)), with Cd(part) >20 μm negatively correlated with Cd(oys) concentration. High phytoplankton abundance in spring and summer was hypothesized to reduce Cd(oys) indirectly by drawing down Cd(diss) and increasing oyster growth. In the present study we expanded on these results by examining specifically how the phytoplankton community composition modulates both Cd(diss) and Cd(oys) concentrations in Deep Bay. Based on calculations of nutrients and Cd(diss) drawdown, phytoplankton accounted for approximately 90% of the overall summer reduction in Cd(diss) in the bay. Diatoms were the dominant phytoplankton group, being correlated negatively with Cd(oys) and positively with Cd(part). This suggests that diatom growth mediates the transfer of Cd from the dissolved to the particulate phase, resulting in lower Cd(oys). Spring blooms and sporadic harmful algal blooms may mediate a large flux of Cd(part) to the sediments. Thus, phytoplankton act as a sink, rather than a source, of Cd to oysters in Deep Bay and have a crucial role in the seasonality of Cd(oys) by reducing the concentration of Cd(diss) during the summer. Based on environmental variables, two descriptive models for annual Cd(oys) concentrations were developed using multiple linear regression. The first model (R(2)=0.870) was created to explain the maximum variability in Cd(oys) concentrations throughout the year, while the second (R(2)=0.806) was based on parameters that could be measured easily under farm conditions. Oyster age heavily affected both models, with the first model being secondarily affected by temperature and the second one being more sensitive to changes in salinity.

Ecological effects of co-culturing the sea cucumber Apostichopus japonicus with the Chinese white shrimp Fenneropenaeus chinensis in an earthen pond

Using net enclosures in an earthen pond, we established three culture treatments with the sea cucumber Apostichopus japonicus and the Chinese white shrimp Fenneropenaeus chinensis: monoculture of sea cucumbers (C), monoculture of shrimp (S), and co-culture of the two species (CS). We measured levels of suspended particulate matter in the water column; total organic matter, total organic carbon, total nitrogen, and carbon/nitrogen ratios in both settling particles and the sediment; and chlorophyll a levels in the sediment. We then compared these variables between the three treatments. We also examined growth, survival, and yield of the two species in the different treatments. From June to September, the mean monthly suspended particulate matter sedimentation rates in the CS and S treatments were significantly (P<0.05) greater than those in the C treatment. From August to November, the mean monthly total organic matter, total organic carbon, total nitrogen, and chlorophyll a contents in the sediment in the CS and S treatments were significantly ( P <0.05) greater than those in the C treatment. Final wet weight, specific growth rate, survival rate, and total yield of sea cucumbers in co-culture were all significantly greater than those of sea cucumbers in monoculture. There were no significant differences among any of these variables for shrimp reared in the two systems. The bioturbation of the sediment and fecal production of the shrimp likely supplied natural food for the sea cucumbers. Co-culture of the two species is a viable option for increasing yield per unit area, maximizing use of the water body, and diversifying crop production.