Multi-level aquaculture device for benthic organisms such as bivalves, aquaculture method, and biofilter using same

An elongate rectangular cultivation box having an open top, is configured so as to allow an outer tank, which serves as a cultivating water storage part, and an inner tank, which serves as a receptacle for bivalves (benthic organisms) S that are to be cultivated, to be both combined and separated. A gap that serves as a water supply opening and a gap that serves as a space in which sediments can accumulate on the bottom of the outer tank are defined when the inner tank is accommodated in the outer tank. Water passage holes are provided in the bottom of the shellfish receptacle (inner tank) and a mesh filter such as netting is stretched across the top face of the bottom. The cultivation boxes are arranged in a vertically stacked manner, with the front portions and rear portions thereof staggered so that cultivation water W that overflows over a front ledge of a shellfish receptacle flows downward into the supply water storage part of a lower cultivation box.

BACKGROUND OF THE INVENTION

The present invention relates to technology for farming benthic organisms such as bivalves, and particularly relates to an apparatus used for farming benthic organisms living in an environment exposed either saltwater or freshwater tides such asvenerupis philippinarum, meretrix lusoria, and corbiculidae, to a farming method and to a biofilter using the same.

Bivalves, of whichvenerupis philippinarum, meretrix lusoria, corbiculidae and the like are representative, are typical popular Japanese seafoods, and are sources of marine protein that can be inexpensively consumed by the general public. Today, however, loss of sand beaches, tidal flats, and the like, due to pollution of ocean waters and rivers, coastal bank reinforcement and the like, has resulted in sharp declines in reserves and catches. Currently, in order to preserve reserves and catches of bivalves, farming is underway in various regions, and in many of the farming methods, spats are artificially seeded on the sea coast and the like and then cultivated in natural environments. However, these conventional farming methods are influenced by changes in the surrounding environment, have high production costs, and cannot provide the market with a stable supply.

Meanwhile, the activities of benthic organisms such as bivalves have an impact on the environment, as they feed by filtering minute phytoplankton that floats suspended in the water and detritus, which is broken pieces of the same, with their gills. In terms of the filtration capacity thereof,venerupis philippinarum, which has a shell length of approximately 3 cm, filters approximately 3 liters of seawater per day, and thus contributes to purification of the ocean waters, from which materials contributing to eutrophication are removed.

Conventional shellfish farming can be divided into mariculture and land-based farming. In terms of farming apparatus in the ocean, spats are cultivated by surrounding a plate or the like, to which spats are attached, with a net and lowering this into seawater, which has the advantage of easily providing an environment that is comparatively close to natural habitat conditions (see JP-3913669-B and JP-3979746-B). However, because the selling price for bivalves is low and production costs are an issue, bivalves remain in a low position in terms of farmed seafood. In particular, costs are presently a problem in terms of achieving land-based farming, and thus this has seen almost no implementation.

For example, in JP-3493357-B, farming facilities for abalone on land are described. In these farming facilities for abalone, an abalone breeding tank is arranged in multiple levels, and the abalone breeding tank is provided with a water supply pipe that supplies seawater and an overflow pipe, while an air supply pipe and a feed supply area are also provided in the breeding tank. Furthermore, in addition to causing seawater to flow into the water supply pipe with a pump, by lowering the overflow pipe, the seawater flows to the lower level water tank, so as to promote the flow of seawater. Furthermore, air is sucked into the air supply pipe with a blower, and compressed air is sprayed out in a froth. Thus, dissolved oxygen is supplied.

SUMMARY OF THE INVENTION

However, with conventional land-based farming apparatus for shellfish, achieving a clean water-environment as one in which tide passage is good, such as is the case where shellfish live, is difficult. Specifically, because the water tended to stagnate, the quantity of dissolved oxygen in the water would decrease and removal of residual feed and excrement was difficult, so that there was a problem in that disease readily occurred. The present invention is directed to solving the problems of the conventional farming technology that could depend only on the natural environment, and an object thereof is to provide a farming apparatus and a farming method that can not only inexpensively and stably provide the market with benthic organisms, such as bivalves, but can also create a flow of fresh water, provide a water environment similar to the natural habitat, and increase the cultivation quantity per unit area, and which can promote the growth of inexpensive and high-quality bivalves without using material such as sand as farming medium.

In order to achieve the objects described above, a first characteristic of the multilevel drawer-type apparatus for farming benthic organisms such as bivalves of the present invention is that of being configured in the form of a rack wherein a plurality of box-type containers are vertically stacked, which serve as cultivation beds for benthic organisms such as bivalves, and which are supplied with cultivation water or immersed in a cultivation water area, and which can be moved between said cultivation water and the air. Furthermore, a second characteristic is that of housing and cultivating the benthic organisms in a densly packed manner in the box-type containers. Moreover, a third characteristics is that of causing the lighting environment of at least the box-form containers to range from indoor daylight conditions to blackout conditions and adjusting the light in accordance with the feeding conditions of the benthic organism being cultivated. Furthermore, a fourth characteristic is that of use as a biofilter, by making use of the filtering capacity of benthic organisms so as to separate a raw liquid containing suspended matter that has been introduced to a farming tank into clean water with low suspended matter, which will serve as recirculation water or aquaculture water, and water with a high concentration of organic pollutants, which will undergo fermentative decomposition and serve as liquid fertilizer.

In contrast with conventional coastal farming methods, which might be referred to as “one-story housing,” the present apparatus can be called “a high-rise housing complex,” whereby production efficiency is dramatically increased. Moreover, in order to improve production efficiency, the stacked cultivation beds are formed as boxes, which are stacked in multiple levels and configured as drawers that can be pulled out of, and pushed into, a water tank or water, which is very convenient for seeding spats, observing cultivation progress, cleaning and harvesting. Furthermore, the bivalves are placed in the box-type containers in a densly packed manner, or slits are provided in the bottom of the containers, in which the bivalves are fitted so as to be upright, whereby groundbreaking effects are achieved in so much as materials such as sand, which were considered to be necessary in the past, are no longer required, and observations of the progress of the shellfish and determinations concerning cultivating conditions can be made at a glance. That is to say, the amount of water supplied and discharged is adjusted in order to control the artificial cultivating environment, but this also facilitates regulation of amounts of pollutants and feed in the water tanks, which dramatically improves productivity. Furthermore, by installing a series of such farming apparatuses, a large-scale farming plant can be developed.

In particular, land-based farming is made possible, but this can also be used on coasts and in rivers, or in paddy fields; for example, this can be used as an ancillary facility in various industries such as by way corbiculidae farming that makes use of paddy fields, or by way of using organic sludge discarded from food industries and the like as feed so that, in addition to obtaining the shellfish as a product, this sludge is purified. Furthermore, because this apparatus can be configured as a single device or as a large scale system of thousands of devices, the range in which it can be used is great, not being limited simply to the field of aquaculture, but rather extending to the supply of raw materials for the pharmaceutical and food industries, ornamental biotope facilities, and from leisure industries such as clam digging activities to large scale production plants.

DETAILED DESCRIPTION OF THE INVENTION

Hereafter, modes of embodiment of the present invention are described on the basis of the working examples illustrated in the drawings.

As shown inFIG. 1toFIG. 3, an elongate rectangular cultivation box2having an open top, which is used as a cultivation bed in the farming apparatus10according to the present invention, is configured as a box-type container in which an outer tank2b, which serves as a cultivating water storage part, and an inner tank2a, which serves as a receptacle for bivalves (benthic organisms) S that are to be cultivated such asvenerupis philippinarum, meretrix lusoria, corbiculidae and oysters, can be both combined and separated. The inner tank2ais formed so as to be shorter in the lengthwise direction than the outer tank2band shallower than the outer tank2b, and is formed so that a gap D1that serves as a water supply opening for water supply from a cock4a, and a gap D2that serves as a space in which sediments can accumulate on the bottom of the outer tank2bare defined when the inner tank2ais accommodated in the outer tank2b. Furthermore, a drain cock (not illustrated) is provided on the bottom of the outer tank2b, so that water containing high densities organic pollutants can be separated and discharged at will. In other words, the relationship between the inner tank2aand the outer tank2bis based on the principle of a water tank configured so as to be partitioned by a raised bottom and a divider plate.

Here, a plurality of water passage holes2eare provided in the bottom of the shellfish receptacle (inner tank)2aand a mesh filter such as netting2cis stretched across the top face of the bottom. Next, the cultivation boxes2are arranged in a vertically stacked manner, with the front portions and rear portions thereof staggered so that cultivation water W that overflows over a front ledge2dof a shellfish receptacle2aflows downward into the supply or cultivating water storage part (outer tank)2bof a lower cultivation box2.

If a plurality of cultivation boxes2are stacked in multiple levels, it is preferable to use a partitioned framework stand (rack)1that allows for stacking without direct contact between the cultivation boxes2, as shown inFIG. 2. The material for the rack1may be any of wood, synthetic resins, metals or the like, but in view of rigidity and durability, it is preferable that this be made from a material such as stainless steel, which has good corrosion resistance. Furthermore, by providing rails on the rack1so that the cultivation boxes2can be inserted and withdrawn on the rack1in the manner of drawers, ease of use will be dramatically improved in terms of observing the cultivated organisms and in terms of harvesting, washing and the like.

The cultivation boxes2according to this working example can be suitably modified depending on the location in which they are installed and the cultivation environment, and there are no restrictions on the shapes thereof, so long as this is a structure that allows the function thereof to be realized. Furthermore, as described above, the bottom of the shellfish receptacle2ais structured so as to allow passage of the cultivation water W that is used for cultivation by way of holes or netting, but depending on the manner in which this is used, it may also be structured so that cultivation water W does not pass through the bottom plate.

As shown inFIG. 2, a cultivating medium6such as sand, which is suited to the type of shellfish S to be cultivated, is spread in the shellfish receptacles2aon each of the stacked levels, and the shellfish S to be cultivated, such asvenerupis philippinarum, meretrix lusoriaand corbiculidae, are placed on this culture medium6.Venerupis philippinarum, meretrix lusoriaand corbiculidae will bury themselves so as to produce a stable habitat. However, as a result of observation, the inventors understood that a cultivating medium6is not absolutely necessary. This is because it was understood that the shellfish will stand upright when fitted into simple slits7, as shown inFIG. 4, and will stand by themselves, supporting each other in a closely packed state, which is assumed to be behavior with which the bivalves S are inherently endowed. Accordingly, with the method in which a cultivating medium6is not used, it is possible to harvest shellfish in a so-called de-sanded state from the beginning.

With the farming apparatus10according to the present invention, after assembling the cultivation boxes2in multiple levels, water is supplied from the top. That is to say, the cultivating area is dramatically increased with respect to the installation area of the apparatus. Note that, in order to cultivate shellfish in the farming apparatus10, aeration must be performed by way of the flow and the falling of the cultivation water (seawater or freshwater) W, and in this regard well-known methods may be suitably selected depending on the manner in which the apparatus is used, or the aeration may be performed using a method that combines these well-known methods.

The bivalves S take-up dissolved oxygen in order to breathe, and take up suspended organic matter in the cultivation water W, which serves as food; the water aspiration and filtration-feeding makes use of the cultivation water W that is directly above the shellfish, where the inhalant siphons and the exhalant siphons are exposed at the exterior of the shell. Accordingly, an important condition for raising these bivalves S is how favorable the cultivating environment of the shellfish S is made. For example,venerupis philippinarumare only capable of aspirating cultivation water W in an area of a few centimeters directly thereabove. It will be appreciated that it makes no difference how good the cultivation water is, or whether feed is present, in layers above this.

In addition, feces from the cultivated shellfish and ejected organic material aggregates known as pseudofeces, which are directly ejected from their mouths, as well as sediments from the cultivation water W, accumulate in the outer tank2b. These organic pollutants will be broken down by bacteria in the cultivation water W, but if there is insufficient oxygen in the cultivation water W, contaminants, such as hydrogen sulfide, which are toxic to living organisms, will build up as a result of anaerobic decomposition processes, and thus, in any case, the cultivated organisms will not be able to survive. In order to avoid this, it is necessary to continue to supply sufficient amounts of oxygen to both the cultivation water W and the cultivating medium6. Furthermore, elution and washout action must be continued in order to prevent the material generated by way of decomposition by bacteria from accumulating. With this apparatus10, a flow is continuously generated in the gap D2by the water that is supplied via the gap D1in each of the cultivating boxes2, so that the ceiling of the gap D2, which is to say the water passage holes2eand the netting2cat the bottom of the shellfish receptacle2a, will also be cleaned.

Thus, the gap D2in the cultivating box2plays an essential role in this farming apparatus, allowing for transport of dissolved oxygen and feed. Naturally, if the cultivation water W in the cultivating box2is not replaced, the concentration of contaminants will increase. It is necessary to replace the cultivation water W in the cultivating box2in accordance with the contamination conditions, but because of the very high ratio of cultivation water W usage by the cultivated organisms S, cultivation water W replacement ratios that would be wasteful can be lowered, and consequently it suffices to replace smaller amounts of cultivation water W, which reduces costs and expenses for equipment such as pumps that supply the cultivation water W.

Furthermore, because the amount of feed in the cultivation water W decreases as a result of the feeding activity of the cultivated shellfish S, it is necessary to provide microalgae and the like in quantities corresponding to this loss, but if there are sufficient levels of feed and oxygen in the supplied cultivation water W or in the stored water W in the cultivating box2, it may not be necessary to supply new feed and oxygen. Furthermore, if one wishes to reduce the cultivating time, an independent circulation system can be employed, wherein no new cultivation water W is injected into the cultivating boxes2from the exterior at any time. For example, as shown inFIG. 5andFIG. 6, a plurality of racks1, which accommodate the cultivating boxes2, may be erected above an aqueous suspension receiving tray3, in which a water supply pipe4is arranged, with a water pump5provided midway. An apparatus of the type that circulates cultivation water in this manner can be used as a biofilter wherein, by making use of the filtering capacity of benthic organisms such as bivalves S, a raw liquid containing suspended matter that has been introduced to the cultivating boxes2, which are farming tanks, is separated into clean water with low suspended matter, which will serve as recirculation water or aquaculture water, and water with a high concentration of organic pollutants, which will undergo fermentative decomposition and serve as liquid fertilizer.

Furthermore, given the behavior of bivalves S, which feed by extending their siphons in dark environments, it is preferable that the degree of the illumination be adjusted in accordance with the feeding conditions for the bivalves being cultivated, by way of the entire farming apparatus10, or at least the cultivating boxes2being covered with a blackout screen, or being in a culvert or the like, so as to produce a state ranging from indoor daylight at 5000 to 10,000 lux to a blackout state, or by way of adjusting the indoor lighting. In other words, situating this in an environment with no greater than indoor daylight levels and controlling the lighting are important elements in promoting cultivation and limiting the proliferation of algae.