Why finfish seed production was unsuccessful in Chile.

Why finfish seed production was unsuccessful in Chile

Masatoshi FUTAGAWA

CORDUNAP

February 24, 2012

There were many finfish seed production projects for decades and majority were failure, a few had produced or none. I have some points of view about the reasons why. Major problem is nutrition of rotifer, particularly feeds for rotifer.

1.      Rotifer culture and handling

1.1. Nutritional value

Rotifer is commonly used for primary live feeds for fish larva. Chile fish seed production use rotifer which is cultured by bread yeast (SMC, Saccharomyces cerevisiae, 4-7 µm) or marine chlorella (NCO, Nannochloropsis oculata, 2-6 µm) and feed to fish larva after enrichment. Besides, it is cultured by concentrated freshwater chlorella (CCV12, Chlorella vulgaris, 2-10 µm, 12 billion cells/ml, vitamin B₁₂ soluble) and NCO. Then it is fed to larva after enrichment in Japan. In 2006, 51 % of hatchery use CCV12 and 92 % use CCV12 and NCO.

Additionally, according to study shows that SMC fed rotifer were totally dead until 3^rd generation, SMC fed at 1^st generation and NCO from 2^nd generation show 20 % lower survival, development time and spawning interval were 1.1 and 1.2 times lower accordingly compare to feeding NCO rotifer. These results suggest that the effect of material diet influenced even next generation by affecting the quality of eggs. Thus, nutritional value of rotifer was low in Chile.

1.2. Size

Usually larva can take 25 to 50 % of mouth size rotifer and according to study, rotifer size composition change, average size not much change, depending on rotifer condition. Particularly, during senescent phases rotifer has no small and big size composition. It will happen if we feed rotifer during senescent phase, larva has not enough rotifer even feed correct quantity.

1.3. Tolerance

According to paper those rotifers (L and S-types) tolerate water temperature changing to maximum 5 ̊C and salinity increase from 26 to 33 pus. For example, if rearing larva in 16 ̊C, it should enrich rotifer below 21 ̊C and rearing below 26 ̊C. Also, salinity in larva tank shows 35 psu, enrichment water should be more than 28 psu and rotifer culture water should be over 21 pus approximately.

2.      Rotifer culture in Japan

2.1. History

In the start of rotifer culture, late 60’s, we fed NCO which required huge outdoor tanks for culture, lot of manpower and land for culturing. Also fed SMC for substitute feeds in early 70’s but they found that the rotifer lacked nutrition, larva had low survival and mal pigmentation even when fed NCO. Then enrichment materials were invented and applied after feeding NCO in 70’s. CCV12 was invented which fulfilled nutritional requirement and production activity was drastically minimized in late 80’s.

Three types of rotifer are cultured in Japan, L-type (Brachionus plicatilis), S-type (B. rotundiformis) and SS-type, which are fed CCV12. Detail of rotifers culture as below.

2.2. Extensive continuous rotifer culture method (ECRC)

There are four culture methods; Batch culture, Partial harvest culture, High density culture and Extensive Continuous Rotifer Culture (ECRC), are operating in Japan. ECRC method was invented lately and produces better quality of rotifer compared to Batch culture in terms of nutrition value and size distribution. Also, the method makes larva strong with high survival and it is operating at 49 % of hatchery in Japan in 2007.

The concepts of ECRC are sustainable stable production with less work activities such as feeding, filter washing and tank cleaning under mass production.

ECRC consist two duplicate large tanks, culture tank and harvest tank, which equipped of four air stones in each bottom corner and both tanks are connected by siphon hose, collecting box to gather rotifer by fine mesh bag-net, feeds tank with metering pump to feed CCV12 continually, fresh and sea water supply to add water continually.

Advantages of this system are as follows.

• ·         Continues water supply allow to long term culture, over a month, due to diluting ammonia and bacteria.
• ·         Long term culture minimizes work activities such as washing tank and restocking.
• ·         Stable production due to constant water supply and harvest.
• ·         Active and wide size rotifer production at exponential and stationary phase due to stable water condition.
• ·         No filter material required due to slow aeration makes particles settle on bottom easily.
• ·         Easy to detect rotifer condition that shows density reduction.
• ·         Harvest tank switch to culture tank, rearing tank become harvest tank, to reverse current direction when productivity down and a culture continue.

Disadvantage is that the system requires large tanks

Actual operation shows that fresh water and sea water supplied to culture tank (25 Kl) continuously, water exchange rate 50 % (12.5 Kl), and rearing water controlled to WT 20 ̊C and Sa 20 pus. Water supply volume  depends on growth rate of rotifer which flow-out to harvest tank to keep rotifer density 120 rotifer/ml. CCV12 fed continuously as volume of 6 L per day (6 ml/10⁶L-type) and harvest 600 million rotifer a daily from Day4 under 35 days culture period.

There are two important points to operating ECRC which maximum water exchange and controlling rotifer growth to adjust feeds. Water supply maintains water quality of system and water volume related to growth rate (water volume = rotifer growth) which depend on WT and Salinity as shown in the table below. However, those factors are not much different to rearing water of larva to minimize a rotifer shock. Thus, you should find ideal WT and Sa to meet maximum growth which related larva culture water.

Second point is it should give 70 % of maximum feeding (5 ml/10⁶L-type or 1.5 ml/10⁶S-type) to limit growth. Because when feeding maximum, the growth fluctuate due to variable water supply and feeds quantity, it happen during operation usually.  Once it happen it is difficult to recover. In the other hand, under feeding rotifer density settles to particular number which depends on availability of feeds without corruption of culture.

2.3. ECRC and SISP combination

Recently, ECRC in combination with SISP (Semi Intensive Seed Production) and seed quality and survival improve with sea bream and black rockfish (49-55).  The method shows that larva culture at harvest tank of ECRC with or without enrichment rotifer. The advantages are produced strong larva, grow fast with less work activities compare to intensive method.

3. Suggestion

Concentrated fresh water chlorella (CCV12) is the key item to prepare nutritious rotifer, produce strong fish larva. Unfortunately, CCV12 is not available in Chile. Bellows are my suggestions.

•    Import CCV12; CCV12 is not much expensive material but problem is to keep the material fresh, keep in cold storage and it should be consumed within a month once open bottle. Possibly, combine orders to make large quantity and minimize freight, deliver under cold chain just after arrive in Chile.
•     Dry microalga; Skretting (ORI-GO culture or green) and Biomarine (Algamac protein plus) supply dry micro alga as a substitute of CCV12. Advantage is longer life than fresh material. However, it needs to improve usage.
•    Semi intensive seed production method (SISP); The method is culture wild copepods in large outdoor tank and produce larva together, feed un-enriched rotifer and Artemia depending on availability of copepods sometime. The method will version up to recirculation SISP (RESISP) and improve survival rate.