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Stalked Ciliates in Biofloc Systems

Shrimp News: York Wang edited this summary of the Shrimp List discussion on Stalked Ciliates in Biofloc Systems.  I added some information that York did not include and lightly edited his report to bring it into conformity with the other Shrimp List discussions that I’ve summarized.

 

York Wong (york_wong@outlook.com): Hi all, I’d like to thank you guys for sharing your thoughts on ciliates (protozoans) in biofloc systems.

 

I started this topic when I found colonies of stalked ciliates on the flocs in my experimental freshwater biofloc tank.  I was not sure whether it was safe to put postlarvae in the tank because some articles suggest they are parasitic.  When I took the following pictures, my autotrophic biofloc tank was seven-days-old and contained ammonia and rice bran, but no shrimp:

 

Picture #1 Colonial ciliates with short stalks 

Picture #2 Colonial ciliates with long stalks 

Picture #3 Colonial ciliates with short stalks (left) and long stalks (right)

Picture #4 A single rotifer

Picture #5 A group of rotifers with a stalked ciliate

Picture #6 A bristle worm with orange spots

Picture #7 A bristle worm and stalked ciliates

 

Nelson Gerundo (nelsongerundo@yahoo.com): Peritrich ciliates (Vorticella, Epistylis, Carchesium and Zoothamnium) like other protozoa are always a part of any aquatic ecosystem.  They do get attached to shrimp, which regularly pluck them off with their chelipeds.  Shrimp also rid themselves of protozoa by molting.  Postlarvae with only one or a few colonies of Zoothamnium on them can still be considered healthy.

 

Giovanni Chasin (gchasin_valencia@yahoo.com.br): Bioflocs usually include ciliates.  If flocs are within the recommended concentration, shrimp will eat them without the risk of fouling.

 

Robert “Hank” Bauman (hankbauman@gmail.com): Vorticella indicates a “friendly” bacterial profile with fewer Vibrios.  I like to see Vorticella in hatchery tanks.

 

Leon Claessens (info@aquaculture-ft.com, http://www.aquaculture-ft.com/home): Protozoan fouling is a clear indicator of the health of the postlarvae (PLs), which should be free of fouling.  Fouling organisms typically attach to the exoskeleton, usually on the head and body, particularly around the gills.  Where the infections are slight, the next molt may remove the fouling without further problems, but in severe cases, the fouling will persist or reoccur in the next stage, indicating poor water quality and necessitating action.  PLs should be examined for any epibiont or organic matter fouling (usually consisting of protozoa such as Zoothamnium, Vorticella and Epistylis) on the exoskeleton or gills.

 

Mark Napulan (kram_lewor501@yahoo.com): Based on my experience with Penaeus monodon, which loves to bury itself in soft muddy bottoms and sludge areas, Vorticella and Epistylis can infect gills and block oxygen.  I saw algal fouling of the carapace when these protozoa proliferated in ponds.  But, in my opinion, wandering, non-burying P. vannamei is unlikely to get an infection.

 

Billy Setio (surijo_setio@yahoo.com): Based on my observations of hatchery tanks, Vorticella always leads to mortalities.

 

Robert “Hank” Bauman (hankbauman@gmail.com): Tilapia green water, when managed properly, will always have Vorticella or Zoothamnium.  These protozoa do not harm postlarvae.  They can be on larvae in poorly managed tanks, but the condition of the larvae is not due to their presence.

 

Eduardo Ballester (elcballester@yahoo.com.br): In one of my papers, I discovered that the number of ciliates in an intensive biofloc system ranged from 39.4 to 169.8 cells/ml, with an average of about 78.9 cell/ml.  The average number of rotifers was about 34.6±47.6 cell/ml.  The average number of flagellates was about 307,000±282,000 cells/ml.  I think those are normal densities of protozoa in microbial flocs.

 

The experiment discussed in this paper was conducted using 15 round floating cages (0.2 m2, 1.5 mm mesh size) in a 7m2 fiberglass tank.  Each cage was stocked with Farfantepenaeus paulensis juveniles (72±24mg) at a density of 250 shrimps per m2 (50 shrimp/cage).  Shrimp feed with 5 different crude protein (CP) levels (25%, 30%, 35%, 40% and 45%) was tested with 3 replicates.  The development of flocs in the fiberglass tank was promoted by strong aeration, molasses, wheat bran and fertilization with a commercial shrimp diet (40% CP).  The carbon/nitrogen ratio in the big tank was adjusted to approximately 20:1 using molasses and wheat bran.  No water exchange was carried out during the 45-day experiment.  Total suspended solids (TTS) were maintained below 500mg/L.  The feed conversion ratio (FCR) ranged from 2.17(45% CP) to 2.64 (25% CP).

 

Martin J.M. Guerin (martin.guerin@yahoo.com): Eduardo, I think that a FCR greater than two and weight gain of only 0.56 grams in 45 days is subpar and may mean that excess organic matter was present in the tanks and could have led to higher than normal microbial populations.  Maybe they were higher than what a good biofloc tank should contain.

 

Eduardo Ballester (elcballester@yahoo.com.br): Martin, Please consider that the species was Farfantepenaeus paulensis, a highly carnivorous shrimp.

 

Nelson Gerundo (nelsongerundo@yahoo.com): In another paper, Eduardo found the number of protozoa (flagellates and ciliates combined) was about 1,400 cells/ml in the biofloc tank at the end of a 30-day experiment.  The number of rotifers was about 150 cells/ml.

 

The experiment discussed in this paper had a very similar design to his 2010 paper (above), but aimed to compare the effect of biofloc as the sole food source on the growth of shrimp.  Farfantepenaeus brasiliensis PLs (25±10mg) were stocked at a density of 1,000/m3 and reared for 30 days.  Limited water exchange (not over 0.5% daily) was carried out by a central drain to prevent accumulation of sludge.  The average TSS was about 257±105 mg/L.

 

In a 2003 paper (Nutrient and Microbial Dynamics in High-Intensity, Zero-Exchange Shrimp Ponds in Belize, authored by Michele A. Burford, Peter J. Thompson, Robins P. McIntosh, Robert H. Bauman and Doug C. Pearson), the number of ciliates in 5 biofloc ponds with 120 white shrimps/m2 ranges from 86-433 cells/ml.  The number of rotifers ranged from 14-114 cell/ml.

 

York Wong (york_wong@outlook.com): Hi all, here are a couple of things I learned from this discussion:

 

Peritrich ciliates, like Vorticella and Epistylis, are part of the aquatic ecosystem.  There’s no need to panic if they are found in bioflocs.  It doesn’t necessarily mean they are on the shrimp.  Since I don’t have a background in aquaculture, I panicked when I saw them with my microscope.

 

If ciliates are found on the shrimp, a few colonies of them might not present a health problem, but dozens of colonies might affect the growth and health of the shrimp by inhibiting molting or causing respiration difficulties.

 

Sources: 1. The Shrimp List (a mailing list for shrimp farmers).  Subject: Stalked Ciliates in Biofloc Systems.  Summary of Discussion by York Wong (york_wong@outlook.com).  July 1, 2017.  2. The Shrimp List (a mailing list for shrimp farmers).  Subject: Stalked Ciliates in Biofloc Systems.  June 28 to July 2, 2017.  3. Bob Rosenberry, Shrimp News International, July 6, 2017.

 

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