Zealand Geoduck Research Articles

Carry-Over Effects of Broodstock Conditioning on the Salinity Tolerance of Embryos of the New Zealand Geoduck (Panopea zelandica)

The New Zealand geoduck (Panopea zelandica) has seen considerable interest from the NZ aquaculture industry. A major bottleneck in culturing P. zelandica is early life stages mortality (e.g., embryo). Therefore, in this study, we investigated the embryonic performance and their transition to the first feeding larval stage (D-veliger) under different salinities (26, 30, 32, and 35 ppt) of four different offspring groups generated from broodstock being fed different ratios (25 : 75, 50 : 50, 60 : 40, and 75 : 25) of the haptophyte Tisochrysis lutea (formerly Isochrysis galbana) (ISO) and the diatom Chaetoceros muelleri (CM) during gametogenesis. Broodstock within all diet ratio treatments successfully conditioned, producing viable embryos. Average egg size ranged between 75 and 80 µm and was not affected by the diet ratios of the broodstock. Survival 48 hr postfertilization, D-veliger larvae yield, and incidence of abnormalities depended on both the embryo rearing salinity and broodstock feeding ratios. The combined salinity of 32−35 ppt and a feeding ratio of 50 : 50 and 60 : 40 (ISO:CM) had the highest survival of embryos (56.0%–77.5%), highest production of D-veliger larvae (>65%), and lowest incidence of abnormalities within D-Veliger (<47%). The size of the larvae decreased with decreasing salinities, with the largest found at 35 ppt (101.22 ± 0.49 µm in shell length). Embryos and larvae did not survive at salinity 26 ppt. These results suggest that diet during gametogenesis can play a role on the offspring ability to cope with environmental stressors at least during the critical first few days after fertilization. These findings provide important information on transgenerational effects due to broodstock diet, especially during the early life stages.

Behavioural and physiological responses of juvenile geoduck (Panopea zelandica) following acute thermal stress.

Climate extremes, such as heatwaves, are expected to become more intense and of longer duration in the near future. These climatic conditions may have a significant impact on the prospects of establishing a new aquaculture industry for the endemic New Zealand geoduck, Panopea zelandica. This study focused on characterising animal behaviour, haemocytes , and heat shock protein (HSP70 & HSP90) mRNA expression following exposure to elevated temperatures, such as those encountered during marine heatwaves around 20°C and an extreme scenario of 25°C, contrasted to an ambient temperature of 17°C. After 24h of heat challenge, P. zelandica were found to be significantly influenced by the thermal changes, as there were differences recorded in all the responses examined. With increasing temperatures, juvenile geoduck were observed to fully emerge from the sediment a behaviour that has not previously been quantified nor associated with stress in this species. The ability of P. zelandica juveniles to re-bury still warrants further investigation, as adults are unable to do so. Haemocyte analyses revealed an increase in the abundance of granulocytes, cellular aggregations, and size of these aggregations at the highest temperature exposure. Increased expression of the hsp70 gene in the haemolymph after exposure at 25°C for 24h was detected and attributed to attempts to mitigate protein denaturation caused by thermal stress. The inter-individual variability in the response of heat shock proteins recorded could aid in future selective breeding programs if it is reflected in net thermotolerance. P. zelandica shows great potential for growing in subtidal habitats around New Zealand, and this study highlights the importance of temperature considerations when selecting potential farm and reseeding locations.

Physiological responses of juvenile New Zealand geoduck (Panopea zelandica) following emersion and recovery

The New Zealand geoduck clam is a unique seafood delicacy, with animals selling for up to $US 220–330/kg. Stress accumulated during transport of juveniles to grow-out sites represent a bottleneck in the aquaculture process. In this study, the physiological responses of juvenile geoducks following emersion (3- and 8-h), and recovery (1- and 5-days) were investigated. An integrated approach of flow cytometry, osmolality and metabolomics, along with behavioural assessments was used. Both cellular and chemical haemolymph parameters and metabolite profiles were recorded for P. zelandica juveniles and are reported herein for the first time. An increase in haemolymph osmolality was experienced with an increase in emersion period, with significant differences seen between the 3- and 8-h emersion groups after 5 days of recovery. Viability measures of haemocytes varied insignificantly between experimental groups, creating baseline ranges. The proportion of haemocytes undergoing respiratory burst activity did not appear to be affected by emersion and re-immersion. Haemocyte mitochondrial membrane potential was highest following 1-day of recovery, likely linked to metabolic readjustment, and increased glycolysis, taking place following emersion. Metabolomics analyses suggest that protein, lipid and carbohydrate metabolite classes assist with energy production in geoducks. Activation of anaerobic metabolic pathways, with a high dependence on succinate, were prominent in the 8-h exposure group, with metabolic recovery still taking place following 5-days of immersion, mainly due to proteins restoring energy reserves. Elucidating the physiological responses of juvenile geoduck subjected to transport stress can aid cultivation methods already underway to develop a novel, high value aquaculture industry.

Effects of temperature on early development of the New Zealand geoduckPanopea zelandica(Quoy & Gaimard, 1835)

Ambient seawater temperature is an important factor during the early life stages of marine invertebrates. Temperature is often manipulated in hatcheries to shorten the incubation period before the larval rearing phase. In this study, the effect of temperature on the early development of the geoduck Panopea zelandica was investigated over a 48-hr period to identify the optimum temperature for fertilization and development in a controlled environment. Eggs and sperm collected from broodstock were exposed to ten temperatures ranging between 11.8 and 23.7°C, and fertilization and subsequent development were monitored over 48 hr. Highest percentages of fertilization were achieved at 23.7°C, which was the highest temperature tested in this study. However, the development of P. zelandica embryos was greatly hindered at temperatures >18.5°C due to a range of abnormalities arising from uneven cell division and cellular blebbing. All larvae died at the highest temperature of 23.7°C within 48 hr of exposure. The combined fertilization success and embryo development data indicate that 18.5°C is the optimal temperature for incubating P. zelandica embryos under hatchery conditions.

Allometric scaling of physiological rates in the New Zealand geoduck clam, Panopea zelandica

The New Zealand geoduck clam Panopea zelandica (Quoy and Gaimard, 1835) is among the largest burrowing clams throughout the world. However, the effects of size scaling on physiology have not been studied for any geoduck species. In this study, we determined the allometric coefficients of respiration rate (RR) and clearance rate (CR) for P. zelandica. The allometric coefficients (β) of RR and CR in P. zelandica were 0.73±0.03 and 0.62±0.07, respectively. Since the clearance rate and oxygen consumption of bivalves are known to scale with dry weight, these coefficients may be used as mass exponent correction in physiological studies for P. zelandica.

Establishing the thermal window for aerobic scope in New Zealand geoduck clams (Panopea zelandica).

Geoduck clams (Panopea spp.) are the longest-lived and largest deep burrowing bivalve. Their unique morphology allows them to live buried in the sediment at depths of up to 1m. The endemic New Zealand geoduck (Panopea zelandica Quoy and Gaimard, 1835) has recently been identified as a potential species for aquaculture. However, very little is known about the biology and physiology of this entirely subtidal geoduck species. Currently, the New Zealand geoduck fishery relies entirely upon wild harvests, but farms are expected to emerge as cultivation protocols are established. A key step in the optimization of cultivation procedures is the identification of optimal temperature and food rations. One method for establishing thermal optima is to identify the temperature window that supports the widest aerobic scope: the degree to which metabolic rate can be increased to support elevated activity demands. Thus, we investigated the aerobic scope for activity at five different temperatures representative of typical environmental conditions (8, 11, 15, 19, and 23°C) for juvenile and young adult P. zelandica. Clearance rate was also measured at all temperatures. Comparisons of aerobic scope for activity and clearance rates between size classes revealed that juvenile geoducks had a narrower thermal optimum than young adults (15-19 versus 11-19°C, respectively). Temperatures higher than 19°C resulted in a reduction of aerobic scope for activity and clearance rate for both juvenile and young adults, which may lead to reduced performance and elevated mortality. These findings provide the first measures of aerobic scope in P. zelandica, a key step towards a meaningful understanding of the ecophysiology of this unusual species.

Functional morphology and performance of New Zealand geoduck clam (Panopea zelandica) larvae reared in a flow-through system

Understanding the parameters required for a reliable hatchery seed production of the endemic geoduck clam Panopea zelandica (Quoy and Gaimard, 1835) is crucial if New Zealand is to develop a geoduck aquaculture industry. To provide the foundation for routine geoduck larval rearing practices, this study reports on physiological, morphological, and behavioral characteristics throughout the larval developmental process. P. zelandica larvae were reared at 17°C and 35ppt, and fed continuously with Tisochrysis lutea and Chaetoceros calcitrans in a flow-through system. The initial veliger stocking densities ranged from 50 to 200larvaemL−1, while residual algal levels were maintained at 20,000 to 80,000cellsmL−1 in three rearing batches. Larval behavior and morphology were described through observation using video recordings, photomicrographs and scanning electron microscopy. The larval development took 16–19days from first D-veliger and metamorphosis occurred across a wide size range (300–375μm shell length). The increase in shell length was linear over time and correlated with the deposition of striae in the prodissoconch II. The ingestion rate followed a power function with time and was closely correlated with the development of the alimentary system, including mouth, esophagus, stomach, style sac, intestine, and digestive gland. Rearing with an initial stocking density of 100larvaemL−1 and residual algal background of 20,000cellsmL−1 resulted in about 76% survival and 15μmd−1 growth rate. The results of the preliminary production trials inform rearing practices and provide biological descriptions that appear to be effective as a baseline protocol for the successful commercial production of P. zelandica larvae. Statement of relevanceThis is the first detailed study of larval development within hatchery conditions for the New Zealand endemic geoduck clam (Panopea zelandica). We identified timing of larval developmental stages, including metamorphosis and growth and feeding parameters that are relevant for successful rearing practices of this species for commercial production.

Effect of neuroactive compounds on larval metamorphosis of New Zealand geoduck (Panopea zelandica )

We present here the first laboratory study on the effects of pharmacologically active compounds on the larval metamorphosis of the New Zealand geoduck, Panopea zelandica (Quoy and Gaimard, 1835). Two batches of competent hatchery-reared larvae were exposed to acetylcholine chloride, epinephrine hydrochloride and excess potassium ions in the form of KCl and K2SO4. None of the tested chemicals increased the proportion of metamorphosed geoducks, and in some cases, the chemical caused significant mortality, despite having been used extensively with other species, such as mussels and oysters. This might indicate that geoduck larval physiology and development differs from other bivalves. Geoducks may have evolved distinct chemoreceptor patterns that facilitate metamorphosis under environmentally favourable conditions for subtidal soft sediment habitats suitable for burrowing. Thus, further research is needed to identify alternative cues (e.g. conspecific adults, sediment characteristics and surface biofilm) and understand their role in settlement and metamorphosis. This information will aid the design of reseeding methods and contribute to the development of reliable hatchery production of geoduck spat.

Aerobic scope and oxygen regulation of New Zealand geoduck (Panopea zelandica) in response to progressive hypoxia

Recent efforts to cultivate subtidal New Zealand geoducks (Panopea zelandica Quoy and Gaimard, 1835) in intertidal areas have been challenged due to daily hypoxia. Hence, further understanding of physiological responses of geoducks of different sizes under different oxygen partial pressures (PO2) is required to optimize their husbandry. Without this knowledge, the risk of increasing cultivation costs due to growth depression and mortality may increase in both magnitude and frequency. Hence, this study investigated the respiration, aerobic scope, critical oxygen partial pressure (PcO2), and oxygen regulation capacity from normoxia to hypoxia in two size classes of fed and starved P. zelandica. The PcO2 was determined to be ~4kPa for all geoduck groups. The respiration rates of fed small geoducks decreased significantly from normoxia (16.7–~21kPa) to mild hypoxia (PcO2–16.7kPa). Conversely, the respiration rates of starved geoducks from both size classes, and large fed geoducks were maintained at a constant level when exposed to the same change in oxygen concentration. However, all geoducks experienced decreased respiration rates during severe hypoxia (0kPa–PcO2). In addition, overall oxyregulatory capacity, assessed using a regulation index, was affected by size rather than by nutritional stress. Large geoducks maintain oxygen consumption across an oxygen gradient more effectively than small geoducks. Also, the aerobic scope of small geoducks decreased significantly with declining PO2, while large geoducks maintained their aerobic scope under hypoxia. Hence, to avoid stress and maximize growth potential of cultivated geoducks, smaller individuals should be grown in areas that remain normoxic, whereas larger individuals may be transferred to on-growing sites that experience periodic hypoxia, potentially including tidal emersion. Statement of relevanceThe New Zealand geoduck clam (Panopea zelandica) has been identified as an emerging aquaculture species. However, efforts to cultivate geoducks intertidally have been challenged due to daily hypoxia. Hence, this study reports on physiological responses (respiration, aerobic scope, critical oxygen partial pressure, and oxygen regulation capacity) of geoducks of different sizes under different oxygen partial pressures to optimize their husbandry.

Biochemical composition of New Zealand geoduck clam broodstock (Panopea zelandica ) conditioned under different temperature and feeding regimes

Geoduck clams are amongst the most valuable cultured shellfish available on the world market, driving interest in the establishment of the native New Zealand species, Panopea zelandica (Quoy & Gaimard, 1835), as a candidate for aquaculture. A critical element of domestication is the effective management of breeding stock to optimize gamete and offspring quality. To develop a reliable broodstock conditioning protocol for P. zelandica, we investigated the biochemical composition of geoducks exposed to nine factorial treatment combinations of temperature (7.5, 11.5 and 16.5°C) and feeding ration [10 000, 50 000 and 100 000 cells mL−1 of a (1:1 cell count) mixture of Tisochrysis lutea and Chaetoceros muelleri]. In addition, a reference group of geoducks was conditioned in an aquaculture pond-nursery system, providing a dilute, mixed phytoplankton culture at ambient temperature. Glycogen, protein, lipid and fatty acid contents of flesh and viscera were measured at days 0, 36 and 73 of conditioning. Glycogen, protein and lipid analyses indicated that geoducks within all treatments achieved a positive energy balance, except for those in the treatment combining the highest temperature and lowest feeding ration. Comparisons of fatty acid profiles of animals among treatments and with the reference group revealed that eicosapentaenoic (EPA, C20:5n-3), docosahexaenoic (DHA, C22:6n-3) and arachidonic (ARA, C20:4n-6) fatty acids were important contributors to gametogenic development for geoduck conditioning.

Broodstock conditioning of New Zealand geoduck (Panopea zelandica) within different temperature and feeding ration regimes

Two-year-old New Zealand geoducks (Panopea zelandica) were conditioned within combinations of three water temperatures (7–8, 11–12 and 16–17 °C) and three feeding rations (10,000, 50,000 and 100,000 cells mL−1 of Chaetoceros mulleri and Isochrysis galbana) for 73 days. Similar percent matured and dry condition index values were observed among temperatures. However, significantly higher dry gonadosomatic indices (GSIdw) were recorded at 8 and 12 °C. Although no difference was detected in percentage of spawned individuals and connective tissue occupation indices, a higher percent matured were recorded when fed 10,000 and 50,000 cells mL−1. A reference group conditioned in pond water became matured 2 months later than the other nine experimental groups, but GSIdw were similar. To maximise reproductive output, we suggest that 2-year-old P. zelandica may be conditioned in pond water for a month and then in 8 or 12 °C seawater with 50,000 cells mL−1.

Fertilization success of the New Zealand geoduck,Panopea zelandica: Effects of sperm concentration, gamete age and contact time

Valuable aquaculture and fisheries industries for the North American geoduck, Panopea generosa, have driven interest in developing similar ventures for other geoduck species including P. zelandica from New Zealand. However, little is known about the fertilization kinetics of this species, or the conditions under which the amount and quality of larvae can be maximized. We determined the effects of sperm concentration, gamete age and contact time on the fertilization success of P. zelandica using an extended-Vogel-Czihak-Chang-Wolf (EVCCW) model. The model provided a good fit to laboratory data when applied to individual contact times. For a contact time of 10 s, optimal fertilization was achieved at concentrations of approximately 10 4 sperm lL � 1 , but this decreased to as little as 10 2 sperm lL � 1 for contact times of several minutes. Optimal fertilization was always <100% (max. observed 70%) and the proportion of fertilized eggs decreased rapidly at sperm concentrations above the optimal. According to the model this was due to a slow block to polyspermy. If commercial hatchery facilities ensure that broodstock are in ripe condition, and use sperm <30-min old, then optimal fertilization can be expected at sperm densities of 10 2 –10 3 sperm lL � 1 at contact times of 5–10 min.

19. Cryopreservation and fertility of geoduck (Panopea zelandica) sperm and oocytes

Geoducks are large salt water clams. They are currently farmed in North America. In New Zealand, there is a small wild fishery for the native geoduck, Panopea zelandica . More recently, there is increasing interest in farming this high value species in New Zealand. Already a small batch has been reared and is ready to be experimentally on-grown on existing mussel farms. Cryopreservation can be a powerful tool for hatcheries and selective breeding programmes for aquaculture. In hatcheries, cryopreservation allows year-round spat supply without the need to condition broodstock for out of season production. This is particularly useful with new species where optimized conditioning regimes have not been established. Spawning techniques may also need development and cryopreservation can enable hatcheries to capitalize on single sex spawnings where gametes would otherwise be wasted. In selective breeding, cryopreservation enables breeders to make crosses on demand; providing them with complete flexibility and enabling faster genetic gains. Towards this goal, we investigated cryopreservation and fertility of gametes from the New Zealand geoduck, Panopea zelandica. Geoducks were induced to spawn during their natural spawning season using thermal shock and serotonin injection. Sperm was collected as concentrated as possible by aspiration and stored at 4 °C before being used in experiments. Oocytes were maintained at either room temperature or 4 °C. For both sperm and oocytes, three cryoprotectants, ethylene glycol, dimethyl sulphoxide and propylene glycol were made up in Milli-Q water and evaluated at final concentrations of 10% and 15% with or without 0.2 M trehalose. For sperm, a simple freezing method utilizing a rack attached to a polystyrene frame which floated the rack 3 cm above the liquid nitrogen surface was evaluated as a method of freezing. Sperm were diluted 1:1 with cryoprotectant solutions and loaded into 0.5 mL straws and frozen on the rack for 10 min before plunging into liquid nitrogen. For oocytes, two cooling regimes were evaluated. Oocytes were diluted 1:1, loaded into 0.25 mL straws and placed into controlled rate freezers that were programmed to hold at 0 °C for 5 min then cool at 1 °C min −1 to −10 °C, hold for 5 min then cool at either 0.3 or 0.5 °C min −1 to −35 °C. Upon reaching −35 °C, straws were plunged in liquid nitrogen. Straws containing sperm were thawed at room temperature. Straws containing oocytes were thawed at 28 °C until the ice had melted. Overall, unfrozen sperm obtained from serotonin injection had slightly higher fertility with fresh oocytes than sperm obtained from thermal shock (70% vs 50% at sperm concentration of 10 5 mL −1 ) The addition of bovine serum albumin to the fertilization assay improved sperm fertility by 30%. Sperm frozen in either 10% dimethyl sulphoxide or 10% or 15% propylene glycol gave the highest post-thaw fertilization rates (>70% at sperm concentration of 10 6 mL −1 ). Oocytes were lysed upon thawing prior to dilution for fertilization. Further work will investigate: optimization and development of cryopreservation methods for both gametes and larvae; the longevity of geoduck gametes and a larval assay to assess subsequent development.

Protandry in the New Zealand geoduck, Panopea zelandica (Mollusca, Bivalvia)

Summary Unequal sex ratios favouring males, especially in younger or smaller animals, is a feature of many infaunal bivalve species, including geoducks. Size and age at sexual maturity, sex ratios, and growth rates of the New Zealand geoduck, Panopea zelandica (Quoy and Gaimard, 1835), were investigated in specimens collected from Kennedy Bay, Coromandel Peninsula, and Shelly Bay, Wellington, from June 1999 to March 2001. Analyses of internal growth bands of polished shell sections were used to determine age at sexual maturity, and to construct von Bertalanffy growth curves for males and females in both populations. Patterns of sexual maturity were equivalent for both populations with 50% maturity calculated to be at ~55 mm and ~57 mm at Shelly Bay and Kennedy Bay, respectively. Length-frequency analysis of geoducks in Kennedy Bay indicated that females became more prevalent as the size increased, with significantly more females occurring in the largest size classes for both populations. However, sex ratios were equal with respect to age after about age 5 years. Similar patterns were observed in Shelly Bay, although the population was made up of larger, older individuals. Protandric development of P. zelandica for a significant proportion of individuals is considered likely for this species as all immature geoducks matured into males in their third year of life. Differences in growth rates could not be used as an explanation for the observed sex-ratio patterns as they were very similar for both sexes in each population. This paper suggests that functional protandric dioecy exists in P. zelandica. This finding may help to explain apparent sex ratio disparities reported in other geoduck species.

Larval development of the New Zealand geoduck Panopea zelandica (Bivalvia: Hiatellidae)

The larval development of the New Zealand geoduck, Panopea zelandica, grown under culture conditions, was described through measurements of shell morphometry using video image analysis, photomicrographs, and scanning electron microscopy (SEM). Gametes were stripped from ripe broodstock and eggs fertilised with a dilute sperm solution. Developing larvae were maintained at 17 ± 1°C. Fertilised eggs developed into trochophores within 12 h and to D‐stage larvae (105.3 μm shell length) within 24 h. Larvae spontaneously settled after c. 16 days at c. 247 μm shell length. Measurements of shell morphology, including total length, total height, hinge length, length of anterior end, and umbo length and height were adequate descriptors of larval development. SEM indicated that the provinculum of D‐stage and developing veliger larvae lacked any teeth, although there was some development of a small lamelliform tooth on the hinge structure of newly settled post‐larvae. Prominent spines common on dissoconch shells of other hiatellid clams were absent in newly settled post‐larvae of P. zelandica. The data presented here are the first description of the larval development and larval biology of P. zelandica. The relative ease of spawning and rearing of P. zelandica suggests that the development of commercial hatchery technology for this species warrants further investigation.