BARRAMUNDI CULTURE

The barramundi, Lates calcarifer (Bloch), is experiencing a dramatic increase in global aquaculture production due to its desirable marketing quality as an established high quality product for the restaurant sector (Figure 34, Anima, 2010).  Being an euryhaline species, its robustness under culture conditions affords the fish good performance over a wide range of environmental conditions, specifically temperature, salinity and water quality (Le Francois et al., 2010).  Fish are protandrous hermaphrodites starting life as males, reaching maturity at around 3 to 4 years of age and later changing gender and becoming females, usually at age 5 years (DPI&F, 2006).  Fish <80 centimetres are generally male, and those >100 centimetres are usually female. The exceptional growth rate of the barramundi makes it an ideal candidate for selective breeding and the implementation of genetic biotechnologies.   Priority research with a concomitant transfer to industry, is focussing on the identification of QRLs (qualitative and quantitative trait loci) which relate to aspects of growth, age at maturation and reproductive characters, environmental tolerances and disease resistance i.e. specific properties of economic value (Carter et al., 2010).  Exemplarily, a barramundi vaccine is  being developed to enable  prophylactic treatment against bacteriological diseases (Barnes, 2010).

LARVAL REARING 3. Harvesting

Figure 31 Harvest Atrium (1)

Postlarvae are acclimated to the farmer’s pond parameters particularly salinity and temperature over a three-day period before harvest.  Postlarvae 14 to 15 are harvested from the nursery tanks by draining the entire 10 tonne tank into a 200 litre harvest bowl (Figure 31).   The ten parabolic nursery tanks and four maturation tanks have outlets interposing to the harvest atrium.  A calibrated cylinder is used for accurate counting of postlarvae with an error factor of  ⁺/^-   5% (Figure 32).  Postlarvae are packed in double layered clean blue bags 490mm x 900mm x 100 microns with oxygen, sealed with an ice packet in styrofoam boxes at 10,000 postlarvae per box. Alternatively, postlarvae are transported directly from the harvest bowls in the 1350 litre transporter tank to the farm site.

Figure 32 Postlarvae Calibrated Counting Cylinder

Figure 33 Harvest Atrium (2)

LARVAL REARING 2. Artemia Production

Figure 27 10,000 Litre Parabolic Nursery Tanks, larvae gravity feed from Larval Rearing Area

Figure 28 10,000 Litre Parabolic Nursery Tank

Figure 29 70 Litre Artemia Hatching Vessels

Live Artemia nauplii are the most important food item available to the Hatchery.  The Artemia utilised should be first grade, 90% hatch rate and preferably sourced from the Great Salt Lakes in the United States of America.  The Artemia room houses six, 70 litre hatch vessels and one x 150 litre vessel (Figure 29).  Artemia cysts are vacuum sealed in 425 gram cans and the expected hatch rate is 270,000 nauplii per gram of cysts.  Cysts are added to the vessels as 213 grams per 250 litres of seawater (Figure 30). Hatching requirements are: temperature set at 30⁰C, full and constant aeration and continuous fluorescent lighting.  Nauplii hatch in 14 to 16 hours, and can be harvested from the conical vessels.  Aeration is ceased, the vessels are lidded and a fluorescent light at the clear base concentrates the nauplii to be drained into a 100 micron bag. Cysts float to the surface of the vessels. Nauplii are washed in freshwater and fed to larvae immediately or stored with aeration under refrigeration for later feeding.

LARVAL REARING 1. Controlled environment

The number of eggs released from a full spawning ranges from 300,000 to 500,000.  Partial spawnings with low hatch viability are discarded.  Egg diameter is 0.3 mm.  Aeration in the bowls is stopped allowing the eggs to settle to the base.  Water exchange is given at a level of 50%.  Ovarian tissue is cleaned from the bowl sides and a 400 micron mesh net is used to remove faeces from the water.  Strong aeration is given in the bowls to keep the eggs in suspension. 

Figure 19 200 Litre Spawning Tanks

Figure 20 1350 Litre Transport Tank

Figure 21 Maturation Tanks

Figure 22 Nauplius 6

 Number of eggs spawned is calculated by taking ten random samples at different places in the spawning bowl with a 100 ml beaker.  Nauplii hatch 12-14 hours after spawning, approximately 3 pm.  Similarly, hatch rate is calculated.  Healthy nauplii exhibit a strong phototactic response. The aeration is ceased and a grey lid is placed over the bowl with a light bulb suspended over a one centimetre hole in the top of the lid to concentrate the nauplii at the surface of the water.   After a period of ten minutes a hose is inserted through the hole and the nauplii are subsequently siphoned into the nauplii catcher bucket (Figure 22).  A secondary hose provides a constant flow of saltwater to the catcher simultaneously.  A 250 micron screen in the centre of the catcher bucket enables effective washing to occur as the nauplii are collected.  This acts to prevent the vertical transmission of viral, bacterial (Vibrio spp.), fungal, microsporidean and other diseases from the broodstock.  Siphoning is ceased before reaching the base of the bowl to leave the weaker nauplii and egg mass together which are then discarded and the bowls chlorinated.  The five tonne larval rearing tanks have been prepared with 250 micron filter screens and one tonne of seawater.  If the ambient water is < 29⁰C the one kilowatt heaters are positioned in the tanks.  The nauplii are inoculated into the tanks at a density of 150 nauplii per litre. 

Figure 23 Zoea 1

There are six nauplii stages in which no feeding occurs as nauplii are absorbing yolk supplies (Wikipedia, 2010) (Figure 23).  Chaetoceros muelleri is pumped into the larval tanks at nauplii 6 at a minimum density of 50,000 cells per mL.  Larvae metamorphose to zoea 1 the following morning and commence feeding (Figure 24).  Zoeal stages 1 to 3 are fed with algae in the ratio of 80% to 20% C.muelleri (at 80,000 cells per ml) to S.tropicum.  C.muelleri must be given at a greater concentration to zoeal 1 and 2 stages as this algae is the appropriate size for ingestion.  The larvae are given feed at 6 intervals throughout the day.  Supplementary feed for zoea 1 to 3 is Inve microencapsulated diet Car #1, at a size 5 to 30 micron.   At zoea 3 stage the larval tanks are at full capacity.  Mysis 1 commences on day 5 and at this stage Artemia salina at 1 individual per ml is added to the tanks (Figure 25). Initially water exchange is at 20%, and then increased to 30-40%.  Inve microencapsulated feed CD#2 (30-90 micron) is added when required.  The algae proportion is inversed for C.muelleri and S.costatum, 20% to 80% at mysis 3 stage (Figure 26).  Postlarvae 1 stage is reached at day 10 when Artemia is provided at 5 individuals per ml.  Bacteriological testing for luminescent Vibrio and Pseudomonas spp. is routinely undertaken by the streaking method using TCBS agar plates.  Probiotic bacteria are used to control the levels of toxic metabolites, strengthen the immune system of the cultured animal and repress the growth of pathogenic micro-organisms. The production of inhibitory compounds by the probiotic bacteria suppresses the metabolism of the pathogens, in addition to inducing competition for nutrients and other resources (Jobling, 2010). Feeding regimes are based on the specific requirements of the various larval stages validated by frequent and detailed examination of the feeding activity of the larvae in each tank.

Figure 24 Nauplii Catcher

Larvae are transferred to the Nursery Section at Postlarvae 1 stage.  The transfer is accomplished by first lowering the tank levels to the line of the conical or in the case of the 5 tonne parabolics, to the one tonne level.  The ball valve outlets of the larval tanks are connected by a section of hose to the inlet of the 10 tonne parabolic nursery tanks which have been filled with seawater to the level of entry (Figure 27).  The process is a moderated gravity flow which affords minimal stress on the larvae.  Postlarvae 1 enter a clean tank environment for the duration of their development to postlarvae 15 (Figure 28).  The feeding schedule consists of Artemia maintained at 5 individuals per ml, by four feeds daily, and supplementary nutrition of Inve Frippak PL+150 (150-200 micron) for postlarvae 1-5, and PL+300 (200 -400 micron) for postlarvae 5-15, supplied twice daily.  

Figure 25 Mysis 1

Figure 26 Mysis 3

3. broodstock

3.1 domesticated stock

A ten year research project undertaken by the CSIRO consortium in conjunction with The Australian Prawn Farmers Association to remove the barriers to domestication of Penaeus monodon (Fabricius) has resulted in major advances in the understanding of the reproductive biology and epidemiology of penaeid prawns (CSIRO, 2010).  Eight generations of selective breeding has substantially improved growth and survival rates (Preston et al., 2009).  The screening of animals for pathogenic viruses e.g. GAV, MoV and MBV using the molecular techniques , in situ hybridization (ISH) and polymerase chain reaction (PCR) assays has brought the industry to the forefront in obtaining specific pathogen fee (SPF) certification (Coman et al. 2009).  The choice of sampling tissue for RT-PCR tests is the pleopod exopodite.

2. marine algae

“Starter cultures” in 250 ml flasks of the microalgae species Chaetoceros muelleri (CS-176/6) and Skeletonema tropicum (CS-604/6) are obtained from the CSIRO National Algae Culture Collection in Hobart.  C.muelleri is predominantly a single celled diatom with a cell diameter of 8-10 microns (Kipp, 2010).  S.tropicum is a colony forming diatom of variable length with a cell diameter of 5.3-23 microns (Louisiana Universities Marine Consortium, 2009; Sarno et al, 2005).  The Algae Laboratory is fully equipped for axenic culture applications with autoclavable borosilicate glassware: volumetric flasks, pipettes, erlenmayer flasks, graduated cylinders and petri dishes.  Working stock solutions and primary stock solutions are routinely composed (Figure 14).  Sterilized seawater from the autoclave (Siltex) (Figure 15) is prepared in two litre flasks with culture medium F2. This medium is made up into stock solutions of the following chemicals:

Ø  Sodium/Potassium Nitrate

Ø  Sodium Di-Hydrogen Orthophosphate

Ø  Sodium Silicate

Ø  Ferric Chloride and Trace Elements

Ø  Ethylenediaminetetraacetic Acid Di-Sodium Salt (EDTA)

Ø  Stock Solution of Vitamins B6; B12 and Thiamine

Ø  (CSIRO Australian National Algal Collection, 2010)

MARINE PRAWN CULTURE 1. hygiene procedures

Hatchery hygiene is of major significance due to the risk of contamination of cultures from outside sources.  Strict hygiene protocols are necessary to maintain a pathogen-free, low risk rearing facility.

Biosecurity in the hatchery is maintained through an integrated management approach, and adhering to levels of quality in practice that provides the desired result. The biosecurity program encompasses these techniques:-