Case Studies on Aquaculture Health in Australia

In a presentation during a session on marine fish and larval rearing innovation, at the Australasian Aquaculture 2008, Brisbane we discussed that Bacillus probiotics are proving very beneficial for fish larval rearing in European and Asian hatcheries, The strains of Bacillus were checked for safety and selected for their ability to inhibit directly bacteria pathogenic to fish, produce exoenzymes to improve digestion and degrade waste products and to grow under a wide range of conditions, e.g. pH, temperature, salinity.

Specific mixtures of these strains of Bacillus are used in commercial products for shrimp and fish larviculture and ongrowing. Using examples from Australian barramundi (seabass, Lates calcarifer) hatcheries, we reported the benefit associated with three products: 

A water quality enhancer and green water substitute for larval fish rearing. It can replace up to 100% of live algae for green water technology, and improves water microbiological characteristics inducing a favourable microbial flora (Sanolife ALG)

 

A microbial water conditioner for fish hatcheries. It may be applied directly in the water of the larval rearing tank or administered via the live food (bioencapsulation) - (Sanolife MIC-F)

 

A microbial water conditioner and pond bottom conditioner for grow out. It is applied during the pond preparation and during the production cycle in order to maintain algal blooms and improve waste degradation (Sanolife PRO-W)

This barramundi hatchery with 4 tanks of 2,000 litres each is located inland. It relies on trucked sea water for the first 20 days of rearing. Freshwater from an underground borehole is used for the rest of the cycle. Probiotic strains that are metabolically active under a wide range of salinity conditions (Decamp et al., 2006, Moriarty et al., 2005), are an added advantage in the rearing of catadromous species such as barramundi. 

Paradise Aquafarm with larval rearing tanks with 25 day old Barramundi

Each tank of full strength seawater (1,000 litres) was stocked with 80 larvae/litre. The tanks were topped up daily with new seawater until day 15 with a maximum volume of 2,000 litres. Sanolife ALG was added daily at a rate of 4g/tonne water, in 2 doses per day, until Artemia feeding started at day 8. Rotifer feeding was stopped at day 10. Sanolife MIC-F was applied at a rate of 5 g/tonne of water, once per day from day 9 until day 24. On day 18, weaning began using Proton 2/4 (200- 400mm),a micro-particulated extruded diet formulated with highly specific raw materials, On day 24, grading commenced with 2mm grader. On day 24, 200,000 weaned fingerlings at 20mm were moved to the nursery, with an overall survival rate of more that 60%.

Overall there was a uniformity of size, with 99% at first grade. Labour was saved compared to previous runs where two to three grades were required before fingerlings reached 2mm. The hatchery owners, Dave and Lynelle McIlvernie, observed that the faeces of the weaned fish were much softer and appeared as such as the feed has been well digested. The bottom of the larval tanks was cleaner than previous runs where live algae had been used. 

Barramundi

This fish hatchery is situated on the Clarence River, and uses brackish water for tank and earthen pond culture of Australian native fish for restocking. The wild Australian bass brood stock are captured and held in tanks to acclimatize, where they are fed 8mm Lansy Breed Maturation soft pellets until spawning is induced.

Before stocking, Sanolife MIC-F was applied at a concentration of 2 g/tonne of water. On day 1 after hatching, 100,000 larvae were stocked in 2 tanks (3,000 litres) filled with green water (fresh algae). Sanolife MIC-F was applied daily at 1 g/tonne water from day 1 to day 28, when fingerlings are transferred to 250m² lined earthen pond. The first 28 days were characterized by static culture conditions: salinity 20 ppt and temperatures ranging between 18 and 20ºC.

The feeding regime included an initial period with rotifers and copepods cultured on Culture Selco High Density, then Artemia nauplii and finally adult copepods and Artemia. On day 28, 100,000 larvae and 60,000 larvae were transferred from the two tanks into two 250 m² and 1 m deep lined fertilized plankton pond. Both ponds were fed a combination of zooplankton and Artemia. Sanolife PRO-W was applied weekly at a rate of 200g/ha per 1 m depth until the ponds were harvested 10 weeks post hatch.

After 10 weeks, the first pond was harvested and 100,000 25mm bass fingerlings were captured and sold for restocking. This was 100% survival. The previous best results had been 18,000 fingerlings from the same size pond. The hatchery operator, Glen Searle, observed that, at day 28, the tank bottom was extremely clean compared to previous runs. There was no black sediment at the bottom of tank and any sediment was grey.

These results from Australia show that the addition of selected strains of Bacillus improves fish production by improving water and sediment quality, thus increasing survival and growth rate. Similarly, the benefits associated with the use of Bacillus strains in Europe (seabream, seabass, turbot) and Asia (Japanese flounder, red tilapia, grouper, rockfish, bream) have been reported elsewhere. The selected strains were from Bacillus species that occur naturally in fish, and other aquatic animals, and thus by improving the health of the animals and improving water and bottom quality, are true probiotics for fish.