Kel Gordon's new sci fi adventure
Kel Gordon's new sci fi adventure
a) the complete knowledge of the life cycle and,
b) developments in our understanding of fish nutrition.
These two factors are the basis of all artificial propagation.
However there are factors that seem to be consistent with most species. For example,
a) hatchery literature often notes that established hatchery reared teleost broodstock generally present fewer problems with more consistent spawning success and,
b) fish breeding techniques evolve and tend to become more simplified with established protocols and efficiencies. But most significant is the adaptation and utilisation of 'standardised' live feed techniques to the development of all larval stage nutrition requirements.
'Modern artificial propagation is a continuum of fish breeding complexities
relative to an evolving nutritional definition and the persistence of technological
refinement'. (Kel Gordon 2003)
This evolution is signified by a general increase in production of both the number of differing species and the density at which the species are cultured. It is not surprising that, the commercial demand driving modern aquaculture development is expected to continue. With declining wild catch fisheries and projected worldwide total fish consumption to reach 110 million tonnes aquaculture is set to surpass cattle production by 2010. (Tidwell 2001).
Discussion
Observations and comparisons on natural reproductive biology of various species have identified a range of strategies for guaranteeing the survival of the species. Indeed there are at least as many strategies for survival as there are species (Hughes 1980).
For example:
a) High fecundity: environmental and genetic
dispersion, significant planktonic larval cycles,
annual spawning cycle based on advantageous environmental signals, large coastal
niche.
b) significant yolk sack nutrition, reduced larval
cycles, live bearing, smaller
established niche environments, reduced genetic dispersion and diversity.
Undoubtedly the most significant commercial development, with respect to fish breeding has been the use of steroids and hormones to manipulate the endocrine system. In the wild, spawning is governed largely by environment queues such as increasing water temperature and photo period. The environmental factors trigger hormonal responses which stimulate maturation as described in the Study Guide and Lam (1982), Nagahama (1983) Yaron (1995) and summarised by Jones (1998).
Hatchery manuals covering most fish breeding
techniques of species, outline improvements in hatchery procedure such as
various barramundi hatchery protocols and Frankish (1991) oyster hatchery
manual for the Sydney Rock Oyster (Saccostrea commercialis) and the
silver perch culture manual (Roland & Bryant 1994).
As shown above, the main controlling applications of fish
breeding are endocrine manipulation and live
feed production. The placement of a species on a propagation complexity continuum
would examine the level of endocrine manipulation and live feeds required
to achieve a commercial result over time and assess this as a percentage cost
of production. Cost is the common factor to all production.
Adding to fish breeding
complexity, Lam (1982) discusses the further potential for endocrine developments
in all stages of modern aquaculture including sex control and growth enhancement
in both hatchery and growout applications. He says, “long term success
of any fish culture operation depends on control of the entire life cycle
of the cultured species”, which supports the reasoning of the continual
evolution of fish breeding
processes.
For example, sex reversal in salmonids, which is induced by addition of opposite-sex,
hormones to induce opposite gonad production. In salmonids this is done to
generate female sperm, which when used to fertilise eggs creates all female
stock with the X-X combination. The technique improves production as unprofitable
precocious males can account for 50% of stock. However the technique is only
used in approximately 50% of production stock in Tasmania (pers. com. N. Forteath).
Crustaceans
Penaeus monodon
“EMBRYO AND LARVAL PHASE Adult P. monodon are believed to spawn predominantly in inshore and to a lesser extent in offshore waters (see Section 3). The eggs are spawned by the female in the water column and soon after sink towards the bottom. The eggs develop through the embryonic phase and hatch out in approximately 12-14 hours. The larvae go through 6 naupliar, 3 protozoeal, 3 mysis and 3 or 4 megalopa substages, with each substage lasting approximately 1.5, 5, 4 to 5, and 6 to 15 days respectively. The megalopa and early juvenile stages are collectively termed postlarvae, or fry for commercial purposes. The postlarval stage begins on day 1 of the megalopa substage. The larvae remain in the plankton for 2-3 weeks and are believed to migrate towards estuaries and mangroves. Five-day-old postlarvae (PL5), approximately 16 days post-hatch at 29°C, end their planktonic phase and settle on the bottom. At this time postlarvae preferentially grasp and cling to filamentous matter, grass, twigs and the like which makes them difficult to sample accurately. It is believed that they migrate into estuaries and mangroves and remain in these nursery grounds until the following summer. (from AIMS Online Publications)”
Palinurid Species
The major aquaculture significance of the life cycle of the spiny rock lobster is time. Time is a commercial cost. And from the figure above it can be seen that each life cycle stage is of considerable time so the adult stage is only reached after approximately 9-11 years. Kittaka (1988) concludes that survival was low and rearing methods inadequate with further ecological and nutritional investigations necessary. In comparison to P. monodon, with 7 months to market size, the growth rate of spiny rock lobsters would hardly support a commercial fishery.
Distribution & Life Cycle
”Both black and greenlip
species of abalone are found around the southern coast of Australia, from
south-west Western Australia to southern Victoria. Blacklip abalone are also
found on the south-east coast, up to Coffs Harbour in New South Wales. Abalone
spawn by releasing eggs and sperm into the water. The larvae are free-swimming,
later settling among rocks to develop to maturity at about 6 years of age.
Abalone do not attach to rocks permanently, and are quite mobile. They mainly
feed on drift- and rock- algae, and the blacklip variety tends to only move
out from cover at night to feed. Their main natural predators are crabs, starfish,
lobsters, and stingrays. http://www.scieng.flinders.edu.au/biology/lm sc/lmscabl.htm”
The long culture period has focused commercial efforts, in Australia, on the sale of the cocktail sized (30-50mm) abalone, which in a wild situation is an immature and illegal size however, worldwide, this size abalone represents a substantial market.
Barramundi is a highly fecund, euryhaline, tropical fish species. It is a high commercial demand species with well-defined fish breeding techniques as shown in figure 13. At hatch, the larvae are approximately 1.6mm and yolk sack absorption is completed on day 2. From the barramundi hatchery protocol chart it can be seen that their diet commences with rotifers and algae which helps maintain water quality and nutritional quality of the rotifers. As the larvae grow their diet changes to suit their mouth size, which is very important factor in larval culture of any species.
Snapper fish breeding is similar to barramundi and is well
summarised at the following on-line site location.
“ Life history: Gonads become ripe in the late spring and in northern waters these fish spawn during the summer months (Oct to Feb, peaking in Dec and Jan) when sea surface temperatures reach over 18°C. During cold years, snapper spawn erratically, with poor results. They are group spawners and gather in large schools, near an entrance to an estuary or in a bay or gulf. While rising and falling in unison in the warm surface waters each fish releases huge numbers of eggs or sperm into the water. It has also been observed that large groups of snapper drift lazily just below the water's surface, barely moving, except to roll over and discharge their gametes into the water. All fish in the group spawn at the same time. Snapper are serial spawners, producing many batches of gametes and spawning several times in one season.
The larvae and very young fish are presumably midwater or bottom-dwelling,
since none have been taken in surface plankton hauls over known spawning grounds.
The smallest snapper generally seen are about 2cm long and probably several
months old. At this small size they are already perfect miniatures of the
adult fish, complete with tiny blue spots along their backs. Snapper grow
slowly and reach a length of 10cm at the end of their first year and do not
mature until they are about 4 years old and about 30cm long. During their
3rd and 4th year, about half of them change sex, going through a hermaphroditic
stage, to become males. By counting annual rings in the ear bones or otoliths
it has been established that the average school snapper is between 4 and 10
years old and that some large snapper may be almost 60 years old. Growth rates
vary considerably depending on local conditions of food, temperature, and
the density of other snapper and a 5Kg fish may be anything between 20 and
50 years old. The oldest snapper are some 60 years old”.
Identify Your Commercial Hatchery Protocol
With a commercial spawning of species such as Barramundi, Snapper
or Silver Perch, especially where outdoor larval ponds are used to on-feed,
the breeding process has to be orchestrated to within a few days to take advantage
of the size and nature of the phytoplankton/zooplankton bloom and how that
relates to larval survival.
An induced spawning may take several days of preparation with tanks and broodstock and ponds and staff. Hypophysation can induce spawning time to within a few hours, which allows much greater control for hatchery management and productivity than to try to duplicate natural spawning conditions for these species. (400um dia. egg 1000-2000iu LHRH-a barramundi/42hour ovulation/280C), (300iu HCG/kg/36 hour silver perch ovulation/260C). See below for an example of hatchery protocol with silver perch and how significant hypophysation is to that procedure.
SAMPLE
Broodstock
Broodstock were maintained in several ponds within 50 km of the hatchery.
Broodstock totalled 400-500 with 2 distinct body shape variations. One short
fattish body and the other being longish and slender in appearance Generally
the shorter fish grew better and were used for commercial farm orders. Records
were kept on the transfer and identification of different batches so as to
maintain a healthy genetic pool.
Broodstock were usually naturally in spawning condition from November until
the end of February although they could be conditioned in the hatchery in
mid winter. Two seasonal spawning runs were possible
Broodstock Capture
Using 120mm mesh gill net usually between 3.30 and 7pm.
Fish were immediately cut from net and sedated with cove oil at 7 drops per
60 litres with aeration. Visual examination confirmed spawning potential of
both males and females.
Fish were removed to the transporter tank in a sedated state.
Back at the hatchery fish were again heavily sedated (4ml/1000litre) and a
sample of eggs and sperm taken by glass pipet.
Hypophysation
If eggs were opaque and not clumped (stage II maturation) the fish was weighed
and injected at 300iu/kg.
Sperm was examined for motility (about 1 per season is non-motile)
Injection time was usually at approximately 9pm. (9pm + 36hrs = 9am)
Males were given a 50% dose injection. But usually males express quite freely.
1 male and 1 female were placed in 1000 litre oval tanks with high aeration
and no water exchange.
Spawning
Spawning occurred 36-42 hours later at 24-260C.
Spawning time was noted and eggs removed 1 hour later (water hard) by dip-net
scooping method.
The eggs were rinsed and volumetrically counted. Average count was 9-13 eggs
per 0.2mls, which averaged 55,000 per litre. With 3-3.5 litres per 2kg female.
Fertilisation was usually better than 95% assessed 12 hours after spawning.
Commence filling ponds at confirmation of fertilisation.
Larval Rearing
Hatching and larval tanks consisted of 200litre plastic barrels with 1 litre
of eggs maximum and vigorous fine bubble aeration. (but not too aggressive)
No water exchange over 3-5 day pre-feeding larval period.
At jaw function/yolk sack absorption, larvae were siphoned and or scooped
and concentrated into outdoor ponds (25,000 larvae/0.25Ha/25-40% survival)
or transferred to 1000litre recirculating tanks for 3-4 weeks of nursery rearing.
They immediately feed on fine dust formulation. However growth was retarded
significantly but once released into ponds 4 weeks later survival percentage
was usually better than 70-80%. Like most larvae they are extremely sensitive
to being handled and dip netting will kill them instantly.
Broodstock Recovery
Spent broodstock again sedated with clove oil and injected with 1 Chloromycetin
dose (3mg/500g) if damaged. Broodstock were kept in tanks for 3-4 days and
then again sedated and returned to broodstock ponds. Spawning mortality was
variable and undefined.
In contrast NSW Fisheries Research at Port Stephens
Snapper breeding program utilises temperature and photoperiod manipulation
only. The hatchery-reared snapper are 5 years old and weigh between 5 and
20 kg. By adjusting the photoperiod and increasing the temperature to 190C
the fish spawn naturally, but “temperature is the key” (Pers com
S. Fielder 2002). “Snapper are asynchronous spawners and can be induced
with this method every few weeks as you can turn them off and on with a few
degrees Celsius”.
Such a system would require continual broodstock maintenance for the year where they are only needed for a few days. It is a costly system to set up and maintain but very efficient in spawning terms. Broodstock maintenance would be a major cost factor for a commercial hatchery, which would probably seek cheaper alternatives unless a continuous batch culture system was being used.
Interestingly, Stuart Fielder stresses that the technique appears simple but has been developed firstly by hypophysation techniques and then over time by assessing where modifications and simplifications could be made. It appears as though once domesticated mature stocks are available the need for hypophysation endocrine control is reduced. Nevertheless, for an asynchronous spawner with only a portion of vitellogenic cells processed to oocyte maturation at any time, perhaps hypophysation was the necessary way to develop the most efficient method. Which is an important point in the process of developing hatchery reared or domesticated broodstock.
In comparison, the same hatchery tanks were used to spawn and rear Australian Bass Macquaria novemaculeate. This species appears very difficult to hold and maturate (pers. com G Allen 1987) so and returned to the hatchery. Wild bass are still injected immediately (HCG at 500iu/kg) due to catch-stress factors, potentially, affecting egg viability.
Once the eggs are fertilised the hatchery processes, eg egg and larval density, types of foods and tank function are basically the same for both bass and snapper (and barramundi as well). Interestingly, due of the biological and environmental similarity, multi-species hatcheries are becoming a trend where such species can be propagated. A recent example is the newly commissioned (2000) multi species hatchery in Broome WA for tropical species.
In another example, at the Port Stephens facility, the blacklip abalone Haliotis ruber is routinely environmentally manipulated to spawn by holding at 15-170C which is similar to snapper maturation. However the water quality must be excellent and recirculating systems don’t appear good enough so water chillers, heat pumps, filtration & exchangers are necessary to duplicate species biological requirements in the flow to waste systems. Ruber can be conditioned in approximately 1200-1500 degree days, which equates to about 7 degree days per day or approximately 200 days at 160C. Spawning inducement is either by UV irradiated seawater (which creates hydrogen peroxide) or by adding hydrogen peroxide (pers. com. Mike Heasman). It is apparent that the natural reproductive cycle is stimulated to spawn (approximately 10 million eggs) with abundant sunlight and rising sea temperature, which would intensify algal blooms. Which, in turn, would be food for the veliger larval stage up until settlement in the natural environment.
Ruber broodstock can be conditioned on a formulated flake diet, which is a recent breakthrough, and maintained in total darkness. The fish breeding process, in this case, is a direct duplication of the wild event. There has not yet been any induced hormonal or steroid development and the broodstock are not yet domesticated as is true of most mollusc propagation. However the significant problem of adequate nutrition which plagued commercial enterprise and broodstock maturation appears to have been solved O’Sullivan (2000).
In comparison to abalone, the Sydney Rock oyster is also efficiently spawned using environmental shock methods. Wild broodstock are abundant but seasonal so maturation methods have also been developed by increasing water temperature to 22-230C and high densities of unicellular algae (3 x 109 cells per oyster per day for 3-4 weeks) (Frankish et. al.1991). The temperature is raised to 280C and the salinity is reduced by 10ppt with consistent results, which again duplicates natural estuarine species spawning conditions. Commercialis is a hermaphrodite filter feeder. The fecundity is very high in all bivalve molluscs and in excess of 20 million eggs per spawning for this species (Frankish 1991). However, even though the spawning procedure is successful, larval survival is still very low for this species.
Stress is a major component and can add substantially to complexity factors. For example, I was fortunate in being a member of the hatchery team for the first barramundi spawning in Western Australia in Broome 2000. It is interesting to note that even though protocols were available it took 18 months to settle the wild stock and hone the procedures before a successful spawning was possible. Certain aspects of procedure will always be site specific but can go unnoticed while following an existing broodstock protocol. Undoubtedly experience, and not just text book theory with species, breeding technique, husbandry techniques and observations of stress are very important attributes for initial staffing of new facilities.
For example, a problem factor with the Broome hatchery was the use of wild stock. It is generally known that stress factors are a major restriction for successful spawning as stress releases maturation inhibiting hormones. Which is why good husbandry techniques are extremely important in calming fish. Procedures of tank cleaning where rushed activity and banging in the tank did little to pacify the wild specimens in this situation. However with a little relaxed attention they can be calmed and hand fed within a few weeks.
In the earlier days of modern aquaculture stress relief was carried out by reduction of salinity for marine species or addition of salt for freshwater species where contact was necessary. However in 15 years of breeding and growout of various species it is obvious that there would have been no industries such as silver perch or barramundi without artificial maturation and hypophysation development. Being aware of that, the most significant single factor in successful commercialisation of hatchery as well as growout and live market procedures was the use of clove oil and other sedatives and anaesthetics. These stress reducing agents certainly revolutionised the live trade silver perch industry in the late 1980’s as handling and transport related stress and mortality were major problems.
Hatchery procedures are now well advanced with P. monodon although
the process still evolves around wild spawners. Bray and Lawrence (1992) summarise
the problem areas but mention there are over 2000 hatcheries using this technique.
They further mention that true domestication is quite rare in any marine shrimp
operation, which could be due to the life span, as they appear to only live
about 2 breeding seasons. In any case this is a highly successful industry
with 663,000 tonnes production 1989 (Bray & Lawrence) rising to approximately
912,000 tonnes in 1998 (Tidwell 2001). P. monodon production is a
major aquaculture component but in perspective represents only 2.4% of the
total aquaculture worldwide (Tidwell 2001) (DeSilva 2000).
Although this species has broodstock domestication difficulties many millions
are cultured each season. P. monodon is arguably the most commercially
successful aquaculture species and its demand continues to grow. The success
of monodon, and other Penaeid species with high demand high return culture,
is also demonstrated by its short life cycle, high fecundity and ability to
adapt to artificial diets.
However this culture has also demonstrated the significant pollution and disease associated with mass aquaculture. How these factors initially and adversely influenced aquaculture but are now causing improvements in many culture aspects is significant as this global aquaculture industry learns from mistakes. For example effluent discharge, where and how farms are constructed, large-scale environmental impact, local community impact and hatchery design and efficiency associated with larval rearing and nutrition. Such a change in strategy may intensify further developments in domestication control efforts.
Larval rearing/Live feed Production Comparisons
The successful development of larval rearing has been largely due to the development of adequate nutrition at an appropriate size food particle. In a wild situation the density of a pelagic cohort is spread over kilometres within a few days of fertilisation so water quality and feed are more a function of the environmental spawning triggers. For example floodwater is a major trigger of both fresh and marine species such as P. monodon and B. bidyanus (McVey 1983) (pers. com. Roland 1990). The nutrient rich waters establishes a slightly time lagging bloom development and consequent food supply for the hatching larval cohort. An event corroborated by the natural life cycle strategy where many species have a first stage non-feeding larval stage such as the trochophore larvae, the nauplii stage and the yolk sack larvae.
However if the same high fecundity cohort is spread over only a few thousand
litres naturally control over nutrition and water quality become critical
to prevent stress, starvation and disease. So a key element in fish
breeding is optimum density. It must be considered
carefully in relation the individual species and natural feeding behaviour.
However, the percentage survival of the cohort is directly proportional to
the quality of hatchery live feed production.
Live feed standards, i.e. unicellular algae, rotifers and brine shrimp are
routinely batch cultured and can account for 50-60% of the floor space and
a significant portion of the cost of production for species with complex larval
stages. Live feeds represent nominal feed particle sizes capable of supplying
adequate nutrition for developing larvae of all species artificially cultured
as shown below.
From the figure below, for prawn species, there are
2 larval stages and a juvenile stage that require feeding. Licop (1988) discusses
the need for unicellular algae and or yeast, for protozoea stages, rotifers
for transitional periods from protozoea to mysis and artemia for mysis to
post larvae. The use of enriched diets appears to be well established and
the use of formulated replacement diets is becoming popular in hatchery trials.
Culture density varies with low culture density “Japanese” method,
the high density “Galston” method with a newer tendency toward
larger 15000,-20,000 litre tanks and individual spawners (Colt & Huguenin
1992), (pers. com. F. Roberts 2002). However one non variable factor in culture
technique was the need to maximise the available energy by feeding the largest
allowable prey size in its highest energetic form (Leger &Sorgeloos 1992).
Disease control has become a function of larval rearing in Australia generally, and quite significant with Penaeid production using a new prophylactic approach. Basically the idea is to optimise single spawner cohorts and utilise recirculating hatch tanks (this process is similar to egg and hatch management of teleost species). The quality of the eggs and the strength of the newly hatched nauplii larvae can be visually assessed prior to transfer to flow through 10,000-20,000 litre parabolic larval tanks (pers. observation True Blue Prawn Farm 2002). Currently the industry appears to be significantly expanding with the construction of several localised hatchery facilities. This move is expected to, not only, reduce the potential for viral and bacterial disease transfer and outbreak but to identify the stronger cohorts for improving growout efficiency. At the same time research institutions are increasing efforts to “close the life cycle loop” and develop the potential of domestic stock for breeding to further reduce disease risk and increase fish breeding efficiency (pers. com. Matt Kenway AIMS).
In comparison to P. monodon studies in the
early 80’s indicated that the culture of the rock or spiny lobsters,
such as Jasus lalandii and Jasus edwardsii were too difficult
for commercial production (pers com N Forteath1983). The 11 stages and high
numbers of intermolts of the phyllosoma (figure 3) development, which lasts
11 months, were unprofitable and significant survival had not been achieved.
However by 1988 Kittaka had developed procedures and feeding regimes that gave a positive result by demonstrating the first successful culture of any member of the family Palinuridae, from egg to puerulus. That process is continually being defined and refined which is noted by work such as Bermude (2002), below, with studies of the larval physiology of each individual stage of Jasus edwardsii as “the behavioural response to environmental factors is essential to control larval distribution in tanks, in order to maximise space and food utilisation”.
One must ask the question where is such exemplary research heading? Here is
a species with an 11month larval cycle and a 2-4 year culture cycle prior
to maturity. Palinurids have a very complex life cycle, which would make it
seem that such research is pointless as the financial potential over 5 years
of culture would be insignificant certainly in comparison to Penaeid species
such as monodon where the culture cycle is 5-7 months.
Bermude 2002
Kittaka (1988) discusses the survival at 0.012% for the first 96 days, which indicates the lack of species environmental and nutritional information. Bermudes work (2002) indicates significant development in the time period but it is still a long way from commercial realisation and the high culture densities required for successful artificial propagation. However Bermudes work is defining the environmental parameters of the complicated larval life cycle, which is where all fish breeding techniques begin. Perhaps there may be a biological breakthrough result or a need to reseed large areas of coastline where such research work would come to the fore.
Demonstrated in barramundi hatchery protocols are the nutritional processes, which signify diet size and density. The size of the larval stages and mouth size are important hatchery factors and are common to all aquatic fish breeding techniques. For example goldfish larvae can commence feeding on freshly hatched and or decapsulated brine shrimp cysts as well as formulated diets. In comparison to barramundi they are quite simplistic in hatchery requirements.
The physical designs of tanks and water recirculation and flow rates etc are
important and relative to the complexity of the spawning and larval stages.
They will always reflect the specific biological requirements necessary to
sustain a cohort in a confined space. Generally however, in terms of fish
breeding complexity, the larval development functions
of a hatchery can be examined as sustaining the cohort both environmentally
and nutritionally.
The hatchery process of a barramundi hatchery protocol is similar for snapper
however the growth rate of snapper is slower which demonstrates the difference
in culture time, temperature and metabolism i.e. 280C and 190C. However the
sizes of the larvae are similar at day 1 of 1.6mm, which allows for similar
feeds and conditions for the larval development period.
Port Stephens Fisheries
Research Fish Hatchery Larval Feed Enrichment and Staging Area
Algae, Rotifers & Brine shrimp
The hatchery procedure is similar for most commercial warm water and tropical teleosts with the more complex species tending to have the smaller larvae and more delicate environmental, feeding, nutritional and feed size particle requirements. A major breakthrough was the recognition of the necessity for high quality nutrition achieved with an enrichment additive for these, more complex, estuarine and marine species. Which has also included improving egg quality by providing high quality nutrition to broodstock. Such species research, for example, barramundi, snapper, Australian bass will lead to artificial propagation of many of the potentially untapped commercial species such as the reef species, Coral Trout Plectropomus maculatus and the Red Emperor Lutjanus sebae.
The hatchery process is not too dissimilar for bivalve mollusc species up until settlement spat. For example the Pacific oyster Crassostrea gigas has a high fecundity and produces approximately 24-50 million eggs of approximate 70-80um in diameter (Loosanoff 1963) and produces a setting stage larvae of approximately 290um in 14.5 days at 270C, (Lipovsky 1984).
First feed mollusc larvae (veliger) feed on unicellular algae in the size range of 5 – 25 microns at 7,500-32,000 cells/ml optimum (Frankish 1991). The algae species, its nutritional value and the culture density of both the larvae and the algae are important factors for strong growth and high % survival. Interestingly, with filter feeders, the first feed particle size is the same throughout its entire life. With S.commercialis this varies from approximately 2-30um while with it’s successful commercial competitor, gigas, the particle size is 2-60um (pers. com. N Forteath 1987).
At settlement, oyster spat (pediveliger 300um day 18-20 at 22-250C) are gently removed from settling surfaces and on grown in upweller flow systems where comparatively high numbers of larvae can be reared in confined areas. This is one advantage factor of filter feeders and upwellers as they create minimal fowling if operated correctly and growth can be quite rapid at this quite significant culture density (pers. observation). For example, screen area = 1590 cm2 with 500um mesh held 190ml of spat which equals 600,000 actual organisms.
An interesting commercially comparative aspect dealing with molluscs applies to the Sydney Rock Oyster and can be defined by reviewing the fish breeding techniques developed overseas for the high demand of the Pacific oyster Crassostrea gigas, and Crassostrea virginica, notably Galstoff (1963) and Wilson (1981). These are complete life cycle analysis and hatchery protocols which demonstrate significant research and commercial application. This research was transferred to research of the Australian species S. commercialis. However the species appeared to be very difficult to almost impossible to artificially propagate (Frankish 1991), (pers. com W. O’connor 2002) even when millions of dollars had been invested in hatchery facilities. Commercially, one must arrive at their own conclusions as to commercial application and process viability and while farmers still rely on wild caught spat.
Wild caught spat is a backward step in aquaculture development but appears
quite valid commercially. The continued use of a method that is approximately
100 years old does seem out of context, technologically but the main culture
limitation is the growout time period.
The "commercialis" industry is an odd pun on outdated industry methods combined with inappropriate research. It is unable to capitalise on the increasing demand now being filled by C. gigas. The failure to break away from the natural life cycle has limited production and cemented a restrictive attitude, that does not reflect the progressive attitudes necessary for commercially viable applications in modern aquaculture.
In another odd technology comparison, successful spawning of Haliotis species has been possible since 1959. Abalone farming quickly became a successful business in Japan and California (Shepard 1976). However developments in Australia lagged and have only become evident as a function of the concern over potential decline of the wild catch industry. This situation is an unusual outcome as Shepard (1976) indicated that both H. ruber and H. laevigata demonstrated very high growth rates and the technology was available (Cuthbertson 1978) to develope commercial species aquaculture. As it can be demonstrated in the above diagrams the larval stages were well known (Shepard 1976) and reproducible spawning technology had been successfully applied overseas. Why the potential of this high priced, high demand export product was never developed, until recently, is an interesting quandary when thinking in terms of profitable aquaculture development. Perhaps answer lies in simple profitability?
In the simplest forms of fish breeding, aquaculture species are live bearing (viviparous) with internal development providing protection and “hatching” of miniature adult forms with functional jaws and instant survival skills. Such species occupy small localised environmental niches where egg and larval stages would not enhance survival. For example, the common freshwater tooth carps (Poecilia reticulata) or guppy, the swordtails (Xiphphorus halleri) and, the mosquito fish Gambusia affinis (Lake 1975).
Other niches require extended larval cycle development such as the spiny lobster Jasus lalandii (Kitaka 1988) and Jasus edwardsii (Bermude 2002). These species insure survival by dispersion and a multi-stage planktonic larval cycle. However such an intricate survival strategy is so complex that it is not possible either technically or financially to utilise fish breeding methods at the present time.
Generally speaking hatchery protocols define complexity and can be considered as a commercial extrapolation of research methods and published experimental data. Broodstock and hatchery protocols can be studied and used as a determining factor for an indication of the progress of the species as a commercial aquaculture species.
For example, the published development work on silver perch hypophysation
techniques Roland (1984), in comparison to Roland (1994) did not change. That
developmental research was then and still is the appropriate, applied commercial
technology. In contrast, the design and efficiency of the hatchery tanks and
larval procedures has improved as well as nutritional developments that allows
for more adequate first feed diets and less reliance on extensive pond culture.
The evolution demonstrates the influence of cost of production on refinement
of hatchery methods and procedures but also alludes to the significance of
hypophysation in fish breeding
evolution.
Endemic disease organisms can be thought of as major opportunistic predators, which exploit both reduced environment quality and increased cohort density. As such they are an ever-present threat to fish breeding and the reason why operational procedures always include prophylactic measures and significant water quality management.
Examples include the inoculation of Atlantic salmon broodstock against Aeromonas
salmonicida and the disease furunculosis, which is now, potentially, a problem
in all aquatic environments and one which is yet to impact on Australian Native
Fish production.
Vibrio disease is a major threat to marine hatchery production worldwide as
well as causing severe outbreaks in growout culture. It attacks most cultured
species at vulnerable egg and larval stages and is difficult to treat once
it has become established.
The major expansion of the cultured shrimp industry, which had little regard
for pollution loading, demonstrates the essential need for responsible production
protocols in both developing and developed countries. The disease problems
created were devastating and coined the term “boom and bust” culture
(DeSilva 2000). The significance for all artificial crustacean propagation
is the increasing incidence, worldwide, of untreatable viral infections, which
will seriously add to the complexity of propagation techniques.
Disease management/prevention is a significant component of fish
breeding and can be a major component of hatchery
technique. Disease is an unknown variable only becoming apparent as a factor
of excessive fish breeding
practices. While sometimes significant production is possible, real or sustainable
production is in providing a density buffer zone between what is possible
and what can be continuously duplicated.
Conclusion
Fish breeding in aquaculture has a considerable range of complexity. The factors that create fish breeding complexity deal mostly with varying levels of biological and nutritional control over life cycle stages necessary to support cohort survival. That control has been demonstrated to be in approximate proportion to the complexity of natural life cycle stages. However complexity issues are also directly relative to a commercial demand competition and cost comparison with existing wild caught product. It is without doubt that the decline in wild caught fisheries has fuelled the development in worldwide aquaculture and the research into artificial propagation techniques. Which incidentally, appears on the verge of major expansion. The demand is also a significant factor in relevant research which ultimately leads to complexity reduction
Increased density of fish breeding has been shown to be a common factor necessary for commercial objectives and the basis for comparing culture complexity issues. Environmental, biological and nutritional technology has developed or is continuing to develop and refine these relative processes effectively reducing fish breeding complexity per species over time.
The quite startling comments by Tidwell (2001) of aquaculture overtaking cattle
production worldwide by 2010 would create a serious argument in many Australian
country hotels. Cattle farming is a way of life here for many so are we naive
or ill informed?.
Have many of the world's problems passed us by because we are a low population density society? Tidwell projected figures for 2030 indicating 50% of worldwide fish protein will be supplied by aquaculture?
One wonders at the future, as these will be exciting times for aquaculture and commercial profits.
But; where will the aquaculture feed come from?
The real complexity is understanding the feed issue and then achieving sustainability.
But where that sustainability exists or can exists is far from the intensive end of production levels we are believing in today.
Or is there another way??? Indeed I believe there is a number of ways.
And that way is not plant protein. Nothing has been achieved in 20 years and yet the funding goes on. Makes me wonder why???
Researchers such as Mr Allen and Mr Carter should bow their heads in shame. They have done nothing for aquaculture.
However, there is no doubt that fish production per hectare is far greater than cattle or for that matter any land animal protein source. And, as well, the quality of aquatic protein is suspected of being more nutritionally in step with human protein requirements.
On a larger, more holistic scale, is aquaculture the next highest propagation complexity factor for survival of 'THE' cohort? Meaning the human population.
Have we over extended our propagation density? Tidwell also states, “it is not that there is not enough fish it is just that there are too many people”.
Perhaps density observations on a cohort survival are much more significant that we ever imagined?
Copywrite Kel Gordon: Master of Aquaculture Degree 2004
Reference Section
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