Nursery System Research Articles

Biological filters in aquaculture: Trends and research directions for freshwater and marine applications

Factors such as limitations in water quality and quantity, cost of land, limitations on water discharges, environmental impacts and diseases, are driving the aquaculture industry toward more intensive practices. This will force producers to adopt environmentally friendlier technologies. Recirculating systems, with a biofilter as the most prominent characteristic, treat internally the water contaminated with dissolved organics and ammonia and reduce the amount of water use and discharge from aquaculture operations. This paper reviews the implications of the changing use of recirculating aquaculture systems (RAS) on biofiltration research for freshwater and marine operations. Demand for cost effective biofilters will increase with the expansion of recirculating systems, both as a complement and replacement of traditional ponds. For freshwater aquaculture, emphasis should be placed in cost competitiveness, low head operations, intensification of ponds with RAS biofiltration and the evaluation of suspended growth systems. In the marine systems, an increase in demand of oligotrophic and ultraoligotrophic systems is expected, particularly in the nursery systems. Sizing and cost efficiency of biofilters for nursery operations should be addressed. Problems in marine biofilter acclimation appear to justify the development of new acclimation procedures. Biosecurity concerns, land cost and storm threats will drive nursery systems inland, where saltwater supply and disposal will force an increased water reuse. Denitrification strategies will need to be redefined and optimized for the marine nursery environment.

Coping with third parties in a nursery pollination mutualism: Hadena bicruris avoids oviposition on pathogen‐infected, less rewarding Silene latifolia

In nursery pollination systems, pollinator offspring usually feed on pollinated fruits or seeds. Costs and benefits of the interaction for plant and pollinator, and hence its local outcome (antagonism-mutualism), can be affected by the presence of 'third-party' species. Infection of Silene latifolia plants by the fungus Microbotryum violaceum halts the development of fruits that provide shelter and food for larvae of the pollinating moth Hadena bicruris. We investigated whether the moth secures its benefit by selective oviposition on uninfected flowers. Oviposition was recorded in eight natural populations as a function of plant infection status, local neighbourhood, plant and flower characteristics. Oviposition was six times lower on flowers from infected than on those from uninfected plants. Oviposition decreased with decreasing flower and ovary size. Moths could use the latter to discriminate against diseased flowers. Although moths show an adaptive oviposition response, they reduce the future potential of healthy hosts because they still visit infected plants for nectar, vectoring the disease, and they reduce any fitness advantage gained by disease-resistant plants through selective predation of those plants.

(61) Pot-in-pot Production of Intermountain West Native Herbaceous Perennials

Low water landscapes are increasing popular and important in the urban areas of the Intermountain West (IMW). Perennial wildflowers are an essential part of low water landscapes, and are a dominant plant type in IMW native habitats. We compared pot-in-pot (PIP) vs. conventional above-ground (CAG) production of six IMW native wildflower species, Mirabilismultiflora, Aquilegia caerulea, Penstemon palmeri, Polemonium foliosissimum, Sphaeralcea grossularifolia, and Penstemonstrictus in #1 (4-L) containers. Media temperature, container-plant water loss, stomatal conductance, and growth were measured during two production cycles per year over 2 years. Growing medium temperatures in the PIP system averaged 10 °C cooler than in the CAG system. Consistent with cooler growing media, overall water loss of PIP-grown plants averaged 10% lower than plants grown in the CAG production system. Lower growing media temperatures apparently affected transpiration, as stomatal conductance was about 60% higher in the PIP system as compared to the CAG-grown plants. The integrated effect of lower growing media temperatures on plant performance resulted in about one-third greater top and root growth for plants growing in the PIP system compared to those in the CAG system. Pot-in-pot production may be an economically suitable nursery system for producing IMW native perennial wildflowers by reducing water loss and enhancing growth.

Effect of stocking density on survival and growth of critically endangered mahseer, Tor putitora (Hamilton), in nursery ponds

Effects of stocking densities on the growth, survival and production of mahseer ( Tor putitora) fingerlings were examined in a single-stage nursery-rearing system. The experiment was conducted for 8 weeks in six earthen nursery ponds having an area of 0.012 h each. Four-day-old hatchlings stocked at 0.6 million/ha was designated as treatment-1 (T 1), 0.8 million/ha as treatment-2 (T 2) and 1.0 million/ha as treatment-3 (T 3). At stocking, all hatchlings were of same age group with a mean length and weight of 1.18 ± 0.04 cm and 0.012 ± 0.003 g, respectively. Hatchlings in all the treatments were fed with Saudi Bangla (SABINCO) commercial fish feed viz., nursery (32.06% crude protein) for the first 14 days and starter-I (31.53% crude protein) from days 15 to 56. Physico-chemical parameters (temperature, secchi disc transparency, dissolved oxygen, pH and total alkalinity) and plankton populations (phyto- and zooplankton) were at the optimum level for fish culture. Highest weight gain was observed in T 1 and lowest in T 3. Final length, final weight and survival of fingerlings also followed the same trends as weight gain. Fingerlings in T 1 produced significantly higher specific growth rate than T 3, but not than T 2. Feed conversion ratio was significantly higher in T 1 followed by T 2 and T 3 in that order. Significantly higher number of fingerlings was produced in T 3 than in T 2 and T 1, respectively. Despite this, consistently higher net benefits were obtained from T 1 than from T 3 and T 2. Overall, highest growth, survival and benefits of fingerlings were obtained at a density of 0.6 million hatchling/ha. Hence, of the three stocking densities, 0.6 million hatchling/ha appears to be the most suitable stocking density for rearing of mahseer fingerlings in single-stage nursery system.

Flow, stocking density and treatment against Polydora spp.: Influences on nursery growth and mortality of the oysters Crassostrea virginica and C. ariakensis

Triploid Suminoe oysters, Crassostrea ariakensis, are currently being considered for culture on the mid Atlantic coast of the USA. Despite studies comparing the performance of C. ariakensis with the native oyster, Crassostrea virginica, at the grow-out stage, growth and mortality of C. ariakensis and C. virginica have not been compared during nursery rearing in upwellers. If, as in grow-out bags, triploid C. ariakensis in upwellers grow at significantly faster rates than diploid C. virginica, they may suffer food limitation in intensive nursery systems at flows and densities where diploid C. virginica do not. If a consequence of the rapid growth of C. ariakensis is a thinner shell with greater susceptibility to boring worms, it may require potentially stressful treatment against Polydora spp. These hypotheses were tested in an orthogonal experiment, done in fall 2003, in which triploid C. ariakensis and diploid C. virginica were grown in upwellers with high (11.34×10 −3 m 3 s −1) or low flow (3.56×10 −3 m 3 s −1), that were treated or untreated against Polydora spp. (by hypersaline dip and drying) and stocked at high or low densities. In the first 2 weeks of the experiment, during which both species grew rapidly, growth of C. ariakensis was up to seven times greater than C. virginica. This difference was reduced in subsequent weeks, when water temperature began to decrease and rates of growth of each species slowed. Contrary to expectation, neither species displayed sizeable reductions in growth at high as compared to low density. Mortality of C. ariakensis was, however, 1–2% greater at high than low density. C. virginica appeared more susceptible to decreased growth at low flow, although the effect of flow in this experiment was small. Both species suffered greatest mortality when previously treated against Polydora spp. The treatment was, however, effective in reducing infestation, to which C. virginica, contrary to expectation, appeared most susceptible. Thus, it appears that similar conditions are suitable for the culture of triploid C. ariakensis in upwellers as for diploid C. virginica.

SUSPENSION CULTURE OF THE GREAT SCALLOP PECTEN MAXIMUS IN GALICIA, NW SPAIN-INTERMEDIATE PRIMARY CULTURE OF HATCHERY PRODUCED SPAT

A technique for growing small P. maximus spat in suspension culture from rafts is described. Hatchery produced spat of initial size 3.0- and 4.3-mm shell height were transferred to a sea-based primary nursery system in May. Scallop spat (3.0 mm) grew to 16.8 ± 3.0 mm during 85 days. Survival was 70.0 ± 8.1%, but decreased due to presence of predators in 33.4% of the sampling units, to between 0 and 37.4%. Important predators were the crabs Atelecyclus undecimlineatus, Liocarcinus arcuatus, and Necora puber and the starfish Asterias rubens. A significant negative correlation was found between Asterias rubens arm length and survival of scallops. Initial shell height affected growth and survival significantly whereas stocking density (50–400 spat quarter−1 and initial coverage of 1% to 17%) had significant effect on growth. Spat of 4.3 mm initial size were significantly bigger than the spat of 3.0 mm after 34 and 57 days, whereas survival was 96.4 ± 4.4% versus 71.4 ± 12.8% after 37 days. No mortality occurred during the second sampling period, but growth was negatively correlated to increased density of spat. The results give important information regarding development of economic production of scallops and showed promising opportunities for optimizing stocking density in intermediate primary culture. The choice of production methods in the next production step (secondary nursery stage) can be based on the results obtained.

Small-scale forestry development in Leyte, Philippines: The central role of nurseries

This paper presents results of survey research into the role of the forestry nursery sector in the development of smallholder forestry in Leyte, Philippines. Seedling production in the province is basically carried out by three categories of nurseries: individual, communal and the government. Seedlings in the government nurseries are primarily raised for free distribution to landholders but the extension scheme fails to reach the majority of the smallholder farmers. Seedling demand of landholders is mostly catered for by the more numerous and accessible individual and communal nurseries. However, problems of capital outlay, sources and supply of germplasm, technical knowledge in nursery management for both timber and fruit trees and low sales are among the major impediments in the sustainability of small-scale nurseries. Most of the communal nurseries fail to sustain the operation after the withdrawal of supporting agencies. Knowledge on site-species matching is needed not only by small-scale nursery operators but also by the managers of government nurseries. It is concluded that the seedling industry in the province is not well established and there is a need to organise better the overall nursery system so as to improve the availability of seedlings and promote appropriate site and species combinations.

Effects of Artificial Substrate and Stocking Density on the Nursery Production of Pacific White Shrimp Litopenaeus vannamei

AbstractNursery production may be enhanced by the addition of artificial substrate to increase the surface area upon which shrimp graze and to serve as refuge. The objective of this study was to assess the effects of the artificial substrate, AquaMatsTM, on the performance of postlarval Pacific white shrimp Litopenaeus vannamei stocked at three densities. Eighteen 230‐L tanks were stocked with 10‐d postlarvae (mean weight < 0.01 g). Six treatments were evaluated and consisted of shrimp stocked at three densities (778 shrimp/m2, 1,167 shrimp/ m2, and 1,556 shrimp/m2) with and without access to artificial substrate. Shrimp in all treatments received a commercial diet ad libitum. After 6 wk, shrimp were harvested from each nursery tank, counted, and batch weighed. Mean final weight, survival, production, feed conversion ratio, and water quality parameters were analyzed by 2‐way ANOVA. There were highly significant (P < 0.001) density and substrate effects on final weight, but there was no significant interaction effect. Final weight was 26.0, 17.4, and 34.5% greater in treatments with substrate than without substrate when stocked at 778, 1,167, and 1,556 shrimp/m2, respectively. There was no significant density, substrate, or interaction effect on survival or water quality. Mean survival was ± 89.1% for all treatments. Increased shrimp growth in the presence of added substrate was likely due to the availability of attached particulate organic matter on the AquaMatsTM that served as an additional food source. Results from this study indicate that artificial substrate can be used to mitigate the potential negative effects of high stocking density on growth of L. vannamei in nursery systems.

The influence of flushing rates, terrestrial input and low salmon escapement densities on paleolimnological reconstructions of sockeye salmon (Oncorhynchus nerka) nutrient dynamics in Alaska and British Columbia

Recent advances in paleolimnology have enabled reconstructions of past sockeye salmon (Oncorhynchus nerka) dynamics using a number of proxy-indicators, including diatoms and stable isotopes. Thus far, studies have focused on nursery lakes with high escapement densities and low flushing rates, ensuring that levels of salmon-derived nutrients (SDN) are high and are incorporated into the food chain. This study examines three oligotrophic sockeye salmon nursery lakes in Alaska (Afognak and Saltery lakes) and British Columbia (Hobiton Lake) to determine if sockeye salmon populations can be tracked in nursery systems with lower salmon escapement densities, higher flushing rates and/or higher terrestrial input. We adopted a multi-proxy approach using diatoms, stable isotopes (δ15N), organic carbon to nitrogen (C/N) ratios and pollen to draw inferences from 210Pb-dated sediment cores. δ15N showed little response to historic variation in sockeye salmon populations, even in Saltery Lake, which has a very high escapement density, and in Afognak Lake, in which average escapement is known to have increased. Dilution effects due to high flushing rates were likely partly responsible for the low δ15N and minimal variation throughout the cores, although very high terrestrial input in Hobiton Lake also dampened the salmon signal. Small changes in diatom species assemblages, however, were evident in all three lakes and may be in response to fluctuating loads of salmon-derived nutrients. Most notably, increases of mesotrophic diatom taxa, such as Asterionella formosa and Aulacoseira subarctica, corresponded to increased salmon production in Alaskan lakes as a result of enhancement (fertilization) activities and climatic changes. Changes in the relative abundance of Cyclotella pseudostelligera in Hobiton Lake may also be in response to a significant decline in sockeye salmon populations off the west coast of Vancouver Island in the 1970s. Other factors, however, such as logging and lake fertilization may also have influenced diatom species composition. These results confirm that, while salmon-derived nutrients may be of key importance in juvenile salmonid development in some lakes, this may not be the case in all systems, especially those in which flushing rates are high. Further, in these systems, diatom communities appear to respond more sensitively to fluctuations in salmon populations (and therefore nutrients) than stable isotope methods, provided that other changes in trophic status are minor.

Influence of Nursery Period on the Growth and Survival of Litopenaeus vannamei Under Pond Production Conditions

AbstractTechniques for head starting or nursing postlarvae (PL) has received considerable attention with regards to nursery protocols, yet there is little data pertaining to the effects of nursery period on the final growout of shrimp to marketable size. This study was performed to investigate the influence of nursery duration on survival and growth of Litopenaeus vannamei during subsequent pond culture. For this research, a single population of high health PL were received from a commercial hatchery and held in a tank for acclimation, quantification, and distribution to nursery tanks or ponds. Treatments included direct stocking of 10‐d‐old postlarvae (PL10) into production ponds as well as the nursing of PL in a covered greenhouse nursery system for an additional 10 or 20 d. After nursing, the PL were harvested, quantified, and transferred to growout ponds. All ponds were stocked at a density of 35 PL/m2 and maintained under standardized conditions. Shrimp were fed with a 35% protein shrimp feed, twice daily during the 112‐d growth trial. Ponds were aerated as needed using a maximum of 19 hp/ha to maintain adequate dissolved oxygen (DO > 3.0). No statistical differences (P >0.05) were found in survival, yield, or growth between treatments. At harvest, survivals during growout were generally higher in ponds with nursed shrimp (77% for PL20 and 79% for PL30) than in ponds receiving PL10 shrimp (67%). Yields were similar between treatments, ranging from 3,525 for direct stocked shrimp to 3,747 kg/ha for those that were nursed for 10 d. Although growth rates of PL under pond conditions will be faster than that of a nursery system, results suggest that a nursery period of at least 10 d helps improve survival during pond production and promotes better size uniformity. Shrimp nursed for 20 d showed little improvement in survival over shrimp nursed for 10 d but did result in a more uniform size of shrimp at harvest.

Solubility of phosphorus and heavy metals in potting media amended with yard waste-biosolids compost.

The potential risk of surface and ground water contamination by phosphorus (P) and heavy metals leached from compost-based containerized media has become an environmental concern. Solubility and fractionation of P and heavy metals were evaluated in media containing 0, 25, 50, 75, or 100% compost derived from biosolids and yard trimmings for potential impacts on the environment. As compost proportion in peat-based media increased from 0 to 100%, concentrations of total P, Cd, Cu, Ni, Pb, Zn, and Mn in the media increased whereas concentrations of total Co and Cr decreased. Except for Cu, all heavy metals in the water-soluble fraction decreased with increasing compost proportion in the media, because of higher Fe, Al, and Ca concentrations and pH values of the composts than the peat. When the media pH is controlled and maintained at normal range of plant growth (5.5-6.5), leaching of the heavy metals is minimal. Incorporation of compost to the peat-based media also decreased the proportion of total P that was water-soluble. However, concentrations of bioavailable inorganic phosphorus (NaHCO3-IP), readily mineralizable organic phosphorus (NaHCO3-OP), potentially bioavailable inorganic phosphorus (NaOH-IP), and potentially bioavailable organic phosphorus (NaOH-OP) were still higher in the media amended with compost because of higher total P concentration in the compost. Further study is needed to verify if less or no topdressing of chemical P fertilizer should be applied to the compost-amended media to minimize P effect on the environment when compost-amended potting media are used for nursery or greenhouse crop production systems.

トマトの低段密植養液栽培に適した底面給液式育苗システムの開発

To increase the efficiency of double-truss tomato cultivation with root-zone restriction, a subirrigation nursery system with row-tray was developed and the growth of tomato seedlings was investigated. The row-tray, a plug-tray for producing seedlings, consists of twenty planting furrows. An irrigation drain sheet (IDS) was placed in five or seven furrows per tray, and both edges of IDS were hanging out of the furrows. After setting the root protection sheet (RPS) and substrate sheet (SS) into the furrows, three seeds were sown at the center of SS and one each 100 mm away from the center on both sides. The row-trays were placed on the subirrigation bed with a water retention sheet (WRS). When irrigation starts, nutrient solution is supplied from an irrigation pipe to WRS and is then sucked up from WRS to SS by IDS. Three tomato seedlings grown connected by SS could be planted to the hydroponics in a lump. Fewer total working hours were required to produce seedlings and planting them into row-tray system than for those using a plug-tray system. In the row-tray system, emergence, plant height and leaf number in IDS attached to the row-tray were greater than those in the non-IDS attached row-tray. There was no significant difference in terms of growth between SS and granular rockwool as a substrate. The final emergence percentage was higher than 95% and there was no positional difference within the row-tray or subirrigation bed with regard to plant height or leaf number of the tomato seedlings.

Small-scale distribution of juvenile gadoids in shallow inshore waters; what role does maerl play?

Abstract The indirect effects of demersal fisheries, such as habitat degradation, are currently thought to be impacting gadoid stocks. Maerl fulfils nursery area prerequisites for several invertebrate species, so its role in similar ecosystem service provision for gadoids has been addressed. Juvenile cod (Gadus morhua), saithe (Pollachius virens), and pollack (Pollachius pollachius) in shallow (<7 m) inshore waters were surveyed with fykenets and scuba off western Scotland over a period of 12 months. Juvenile densities were highest from September to November, and at that time, significantly more were present during the day and associated with maerl (that lacked macroalgal cover) than with heavily vegetated rocky and gravel substrata. Juvenile cod were present throughout the year, whereas saithe appeared in July, and pollack from September to January. With its abundance of food, maerl probably has a high holding capacity for juvenile gadoids, and thus is an important part of the inshore nursery system.

Development of Nursery Systems for Black Sea Bass Centropristis striata

AbstractBlack sea bass (Centropristis striata) are territorial fish and cannibalism is a concern when rearing juveniles in intensive systems. Three studies were conducted to provide information for development of suitable tank nursery systems for juvenile black sea bass (3.6–4.5 cm; 0.8–1.7 g). Studies were performed at the Marine Resources Research Institute, Charleston, SC, using 1.5‐m diameter × 0.8 m deep tanks connected to recirculating seawater systems. The studies examined growth and survival at different stocking densities, selection and utilization of habitats, and, effects of water velocity on positioning and movement of fish. In study 1, fish were stocked at biomass densities of 126.7, 253.3, and 506.7 Wm3 and reared for 56 days with no habitats. No difference in growth was detected although fish reared at the lower densities had significantly lower mortality (mean 7.9%) as compared to those at the highest density (28.0%). At the highest density, cannibalism appeared to be a substantial cause of mortality. In study 2, three habitat types were used, (1) two‐tier structure constructed from plastic grating with 15 mm square openings (volume = 0.015 m3); (2) PVC pipe bundle (volume = 0.004 m3); (3) rock aggregate (volume = 0.008 m3). Of the habitats, the most utilized habitat (62.9%) was the two‐tier layered structure that allowed movement in all directions. The next utilized type was the pipe bundle (25.6%) with the openings inhabited by the largest juveniles in each tank. Overall, a mean of 18.2% of the fish were observed using habitats. Study 3 examined water velocities ranging from 0.01 to 0.12 m/sec. Most fish became concentrated in the tank bottom area having a water velocity in the range of 0.040.09 m/sec. At these velocities there were few aggressive interactions. Smaller fish inhabited the areas outside this velocity range. At the higher velocities, the small fish swam vigorously to maintain their position in the water column. At the low velocities, sporadic incursions of larger fish occurred presumably to attempt to cannibalize or to defend territory. Results from these studies help to define characteristics of nursery systems for rearing juvenile black sea bass.

United States Department of Agriculture-Agricultural Research Service research on alternatives to methyl bromide: pre-plant and post-harvest.

Methyl bromide is a widely used fumigant for both pre-plant and post-harvest pest and pathogen control. The Montreal Protocol and the US Clean Air Act mandate a phase-out of the import and manufacture of methyl bromide, beginning in 2001 and culminating with a complete ban, except for quarantine and certain pre-shipment uses and exempted critical uses, in January 2005. In 1995, ARS built on its existing programs in soil-borne plant pathology and post-harvest entomology and plant pathology to initiate a national research program to develop alternatives to methyl bromide. The focus has been on strawberry, pepper, tomato, perennial and nursery cropping systems for pre-plant methyl bromide use and fresh and durable commodities for post-harvest use. Recently the program has been expanded to include research on alternatives for the ornamental and cut flower cropping systems. An overview of the national research program is presented. Results from four specific research trials are presented, ranging from organic to conventional systems. Good progress on short-term alternatives is being made. These will be used as the foundation of integrated management systems which begin with pre-plant management decisions and continue through post-harvest processing.

Growth stimulation of ectomycorrhizal fungi by root exudates of Brassicaceae plants: role of degraded compounds of indole glucosinolates.

Brassicaceae plants are nonmycorrhizal. They were found to inhibit VA mycorrhizal infection in their host plants. We tested if they can influence growth of ectomycorrhizal (ECM) fungi. When roots and leaves of Brassicaceae plants and ECM fungi were cultured together in the same petri dishes, the root exudates of turnip (Brassica rapa), swede (B. napobrassica), cabbage (B. oleracea, var. capitata), broccoli (B. oleracea, var. italica Plenck), kohlrobi (B. caulorapa Pasq.), mustard (B. juncea), radish (Raphanus sativus), and choy (B. napus) significantly stimulated hyphal growth of the ectomycorrhizal fungus Paxillus involutus. Root exudates of turnip and cabbage stimulated hyphal growth of Pisolithus tinctorius and two isolates of P. involutus. Colony area of P. involutus was increased by 452 and 414%, respectively, in the presence of turnip and cabbage germinants. Root exudates of turnip increased the biomass of P. involutus and P. tinctorius by 256 and 122% and cabbage by 220 and 82%, respectively. The stimulatory effect was not affected by autoclaving the root exudates. Root exudates had chemical reactions with glutathione and lysine, which resulted in a reduction of the growth stimulation of ECM fungi. Myrosinase enhanced further the stimulatory effects of turnip on the ECM colony diameter growth by 23%. Autoclaved roots and leaves of turnip did not stimulate fungal growth, but mechanically ground roots and leaves of turnip stimulated growth of P. involutus by 147 and 135%, respectively. After desulfuration with aryl sulphatuse, the glucosinolates (GLSs) in turnip roots and leaves were identified by HPLC. The major ones were indole GLSs. Prominent compounds identified were 1-methoxy-3-indolymethyl GLS and4-methoxy-3-indolymethyl GLS. The finding provides an opportunity to field test the use of Brassicaceae plants in enhancing ectomycorrhizal formation in conifers by interplanting conifers with Brassicaceae plants in forest tree nursery and agroforestry systems.

Conflicts between plants and pollinators that reproduce within inflorescences: evolutionary variations on a theme

The high diversity of mutualisms has probably limited the development of a general theory about their evolution and their stability. Here we review conflicts of interests occurring in the 13 known nursery pollination systems, where pollinators reproduce within the inflorescence they pollinate. We found three main conflicts of interest between mutualists that correspond to the following evolutionary questions: 1) Why do plants not kill their pollinators’ larvae? 2) Why do pollinators visit deceptive flowers? and 3) Why do pollinators pollinate? We show that the reproductive system of the plant is strongly correlated not only with the set of conflicts of interests that actually occur but also with the proximal resolution of these conflicts. In many cases the evolutionary stability of nursery pollination mutualisms relies on the avoidance of intra‐specific competition among pollinator larvae. This stabilizing factor could perhaps also explain the absence of overexploitation in other mutualisms.

Mycorrhizal Fungi in Rooting Substrate Influences the Quantity and Quality of Roots on Stem Cuttings of Hick's Yew

In a commercial nursery propagation system for hick's yew (Taxu×media `Hicksii'), we assessed whether or not the addition of inoculum of the vesicular-arbuscular mycorrhizal fungus (VAMF) Glomus intraradices into the rooting substrate during cutting propagation increased rooting, and how the quantity of inoculum influenced rooting. At 15 and 22 weeks (108 and 156 d) after cuttings were treated with root hormones and stuck, root initiation was higher on cuttings stuck in the rooting substrate containing VAMF inoculum. Increasing the quantity of inoculum in the rooting substrate increased root growth during the early stages of rooting. However the highest level of inoculum tested increased adventitious root initiation without increased root growth. Our results indicate that if VAMF inoculum is used during propagation from cuttings, there are optimal levels required to alter the initiation and growth of roots. For hick's yew, 1:100 or 2:100 (by volume) rates of G. intraradices in the rooting substrate increased the number of primary roots and growth of adventitious roots on cuttings above that achieved by using rooting hormone alone.

Intensification of redclaw crayfish Cherax quadricarinatus culture : I. Hatchery and nursery system

Intensification of an indoor hatchery and nursery system for the Australian redclaw crayfish Cherax quadricarinatus (von Martens) (Decapoda: Parastacidae) was obtained by increasing the surface area available for the crayfish juveniles and by synchronizing the age of the hatchlings held in each tank. The former improvement was facilitated by distributing an artificial seaweed-like material throughout almost the entire volume of small (275 l) hatching tanks. As the number of egg-bearing females was increased from 3 to 8 per hatching tank, the number of juveniles per liter also increased to as many as 6.5 juveniles/l, without reaching an apparent upper limit. The hatchlings were kept in the tanks for 75 days from the day females were found to be gravid and then harvested and graded according to size. The average juvenile weight at harvest was 0.34±0.04 g. The weight distribution of the juvenile males was not significantly different from that of the juvenile females on the day of harvest, and in both the distribution was positively skewed.

Alternative means of nursery culture for commercial scallop ( Pecten fumatus Reeve) spat

Difficulties in controlling settlement densities of hatchery-produced Pecten fumatus larvae on mesh-filled collector bags prompted an evaluation of two alternative nursery-rearing protocols. In both cases, larvae were initially settled and on-grown on mesh downweller screens in the hatchery. In the first protocol, spat were retained on conventional downweller screens until it is large enough to be transferred to a field nursery system comprising tiered stacks of mesh screens located in upwelling systems. Mean growth rates were greatest for spat held on the first (most upstream) of eight screens within each stack and exhibited a progressive decline in successive downstream screens at all densities tested. Daily rotation of screen position within stacks overcame differential spat growth and significantly increased overall mean biomass gains. Stocking density per unit surface area of screen is critical in determining growth rate of P. fumatus spat in field upwellers. Irrespective of other growth-limiting factors such as food, the upper limit of stocking rate at which maximum growth rate is maintained is approximately 70% screen coverage. Although only marginal reduction in growth occurs at stocking rates of up to 100%, screen stocking rates above 70% coverage are not recommended because of the problem of death and damage that occurs through inadvertent clamping at higher densities. Maximum growth rates recorded for P. fumatus spat held in a single tier upweller screen coincided with high flow (l min −1) to biomass (kg) ratios of 20 to 30:1. Reuse of seawater via tiered upweller stacks enabled in the case of an eight-tiered stack up to a doubling of yield per unit of seawater flow. Optimised production efficiency would appear to coincide with use of about six to eight tiers per stack and daily alternation of screens from the top to bottom locations within the stacks. In the alternative nursery-rearing protocol, P. fumatus were settled on mesh screens using inexpensive nylon curtain material and retained in the hatchery for periods of 1–5 weeks post-settlement. The mesh from each screen was removed and was cut into sections with the desired number of spat attached. Each section was placed in a spat collector bag stuffed with conventional coarse plastic netting and was then deployed to the field. Subsequent survival of scallops after 30 days was found to depend on spat size at the time of deployment and upon handling methods used during deployment. The percentage of 500–750 μm spat (2–3 weeks post-settlement) recovered at a size of >5.0 mm, suitable for transfer to grow-out facilities, was 25–30% and comparable with that achieved in tiered upweller nurseries. However, screen to collector bag transfer requires less capital outlay and is less labour-intensive than tiered upweller systems.