SHRIMP BROODSTOCK MORTALITIES
From: Ben Williams firstname.lastname@example.org
Sent: 30 January 2003
I received a question from a friend in the
Philippines and I was hoping that the list could offer some thoughts and
opinions on what is happening. Please see below:
"We would like to ask your expert opinion, regarding the present problem being encountered by our hatchery operators wherein they experience high mortalities in their spawners (broodstock).
The mortalities occur 3 days after being caught in the wild or after they
have performed oblation of one eye to initiate egg production.
Due to this situation, hatcheries can not operate in full capacity and have caused temporary shortage of good quality spawners with prices sky high.
Some of the experienced hatchery operators are blaming it on the wide
variance of temperature between the day and at nighttime, which causes too much stress.
We are referring this to you hoping that you might have experienced similar situations in the past and have already formulated some control measures to prevent or correct this situation."
What temperature variations do they have?
A combination of ablation and temperature variations could stress the
animals and allow some pathogen to cause mortalities. What is usually done with pond raised animals is a two weeks treatments with some medicated feed (antibiotic). For wild caught animals it might take longer to eliminate stress...but if it's a virus antibiotics won't help anyway. Have you done any screening?
Don’t know much about Monodon broodstocks but there
is a chance these are wild caught animals with unknown history like Francois
says, maybe latent pathogens.
In any case I would also consider an acclimation / quarantine time of
several weeks prior entering in production but again it may not fit with
"traditional" Asian method using riped wild spawners.
My best suggestion here is to consider changing working method and purchase quality RAISED broodstocks or to implement a broodstock program within the company.
It would be important to know how long they keep the
animal between catching them in the wild and perform the ablation.
This period is very important because the wild animal must absorb the stress
to be capture in the wild before "receiving" a new stress by the
ablation. The bets is to keep them in quarantine tanks, this thank
could be outdoor lined ponds. This time is at least of ten days, but
it is no rules, daily observation will let you know, when you will be able
to transfer them in maturation and practice the eyestalk ablation.
The technique you are using could also have an influence on the mortality rate. I would recommend to realize a ligature with some chirurgical thread on the eyestalk before cutting it. This will reduce the bleeding. After the ablation, it would be suitable to disinfect the wound.
In this situation, it not the stress that stress out
broodstocks, as it now happening to mass hatchery in Phillipines. In order to rectify, is to source the Monodon broodstock from other sea area. There would not be a huge demand and high price for the broodstocks and naup, if there is no mass mortality of the broodstocks. In Monodon naup production, 60% depends on broodstocks, 30% on water, and 10% on techniques (for monodon only, not sure for vannamei).
COMMENTS 5 :
High mortality rates are common with wild broodstock,
before and after eye-stalk ablation. Mostly, mortalities are due to the
stress caused by tank transfers, ablation and sourcing. From what I
understand, the mortalities are already observed before ablation. If there
have been no changes in management practices (feeding, stocking density,
acclimation period, temperature), a sudden increase in mortalities may
indicate problems (often seasonal or dependent on lunar cycle) related to:
1. source: different source (possible solution: try to shorten the
transport time from the sea to the hatchery, cooling of transport tanks, use of individual nets rather than perforated PVC tubes)
2. water quality: increased run-off water or changed ocean currents can increase organics and/or heavy metals (possible solution: time pumping in function of water quality; use 10 to 15 ppm EDTA to chelate heavy metals)
3. disease (together with 1. and 2.): parasites, bacterial and viral
pathogens, .... may have been introduced or may just cause more harm because animals are stressed by other factors like those mentioned in 1 and 2 (possible solutions: diagnosis of the disease and treatment with chemicals, antibiotics, ...., in the worst case you need a dry-out period)
It is sometimes difficult to find one causative factor, but if this is not
just a seasonal effect that is experienced every year, there must be a way to find out what is different from the "usual" conditions and try to tackle this. Please keep us posted on how this problem evolves and/or how it was solved.
Your statement, "wide variance of temperature
between the day and at night time" raises some questions. Presumably,
these are collected on board trawlers or small boats, in which case the
temperature fluctuations will be even wider. However I think extremely high
temperatures will be more stressful than low (down to 20°C) temperatures,
but the fluctuation range will also be significant. Stress effects are
exponential so a small final stress can kill an already heavily stressed
So, to answer your own question, you need to trace the handling history of these broodstock. Also, what is the transport method to the hatchery (again, especially very high temperatures in bags) and what is the acclimation method? If the broodstock come from a low salinity area, say 10ppt (i.e. bagged water holding broodstock is 10ppt) and they are simply dumped into your maturation at 30ppt, probably 60% will die, especially when already stressed.
I got wild spawners from many areas in the
Philippines during the 80s-90s.
The most reliable, for whatever reasons, were from Masbate and Samar, Layte areas in the Central and Western Visayas. Bohol, for some reason produced low surviving nauplii. Negros area had some good, but some bad. The points others are bringing up are very important, such as handling stress etc, but I found I had little or no control on quality handling from boats catching them to spawner gathering station. My selection was based solely on performance in the hatcheries.