The Fish Vet's Blog

I’ve been asked about what the optimal stocking density for fish are. I tell them it depends.

If they’re schooling fish (e.g. sardines), then they’d be less stressed if held in higher stocking densities. However, if they are territorial fishes (e.g. male Siamese fighting fish) then the answer would be quite the opposite.

In terms of fish farming, even though the question asked may be due to pure economics, overstocking –>; stressed fish –>; unhealthy fish –>; disease –>; fish losses –>; profit losses.

So n terms of satisfying the biological-type definition of fish welfare, this work done on the cod is good.

Aquaculture
Volume 357, Number 3 (August 2012)
	Optimal stocking density of juvenile Atlantic cod (Gadus morhuaL.) reared in a land-based farm
	Authors:	Björn Björnsson, Agnar Steinarsson, Matthías Oddgeirsson, Sólveig R. Ólafsdóttir
	Author Affiliations:	no affiliations available
	Source:	Aquaculture, Volume 357, Number 3 (August 2012)
	Page Numbers:	342 – 350
	Available Full Text:	Full Text: Subscription Required to view full text Format: PDF Size: Unknown Location: Publisher’s Site Authentication: Publisher’s Site
	Abstract:	The effects of stocking density on the productivity in a juvenile cod farm were studied in a flow-through system for fish weighing initially 44g. The fish densities increased throughout the experiment from 4 to 21, 11 to 54 and 22 to 95kg/m3. Growth rates were negatively affected at densities above 50kg/m3and at the end of the experiment the mean weights were 242, 221 and 205g at low, medium and high densities, respectively. The average cumulative mortalities increased with density and were 1.8, 4.2 and 7.3% of initial number of fish at low, medium and high densities, respectively. Antibiotics were administered twice at high, once at medium and never at low density. The average feed conversion ratios were 0.81, 0.91 and 1.02 at low, medium and high densities, respectively. The average biomass increase was 16.8, 42.7 and 72.8kg/m3at low, medium and high densities. A simple economic analysis indicates a parabolic relationship between profit and density with optimal density at the peak of the curve. Given reasonable assumptions about production costs in a land-based farm, the break-even density is 35kg/m3and the optimal final density is 95kg/m3. Changes in fixed costs, such as financial costs and salaries, have no effects on the optimal final density whereas changes in variable costs, such as feed and juvenile costs, directly affect the optimal final density.
	Citation:	Björn Björnsson, Agnar Steinarsson, Matthías Oddgeirsson, Sólveig R. Ólafsdóttir . Optimal stocking density of juvenile Atlantic cod (Gadus morhuaL.) reared in a land-based farm. Aquaculture, Volume 357, Number 3 (August 2012), pp. 342-350, ;
	URL:	http://ejournals.ebsco.com/direct.asp?ArticleID=4C0A9BEB69DA67B80FF0

http://www.thefishvet.com.au

I just uploaded a video of fish showing the classic clinical signs of white spot disease.

http://www.thefishvet.com.au

Fish Vetting Essentials

This is a comprehensive guide which provides information not only on Fish diseases and medicines but also on the basic anatomy of fishes, categories of fishes, water quality parameters, diet and nutrition. Being a person who is working in the field of ornamental fishes for the last 20 years, I wish to comment that anybody who does not even have basic background of fish biology can use this book as a ready reference. Chapter on aquarium set up and water quality parameters provides very useful tips to aquarium hobbyists. Water sampling procedure and fish disease investigation are topics of great interest and use to fish farmers. Worthy of note is the photographs with which diseases can be identified. It contains a wealth of topics which has quick and easy accessibility.

Fish vetting medicines provide a wealth of information on medications that may be available for use by fish health professionals in the treatment of fish diseases. Both these books will be an asset to any fish keeper’s bookshelf/vet clinic.

Dr. T.V.Anna Mercy

Professor

Faculty of Fisheries

Kerala University of Fisheries and Ocean studies

Panangad, P.O., Kerala, India

91 484 2306001

91 484 2700598

91 9447667069

This book can be purchased from http://www.thefishvet.com.au

On Wednesday the 25th of July I attended a webinar about the research that has been conducted with the killer koi virus. It was provided courtesy of the Australian Biosecurity Intelligence Net-work (ABIN). Veterinary virologist Dr Ken McColl provided some background, and recent progress, on an Invasive Animals CRC-funded project entitled “Koi Herpesvirus – a potential biological control agent for carp in Australia”.

Despite many failed attempts at utilising biological warfare to control vertebrate “pests”, Australia seems to want to do it again. It was said that the exotic killer herpesvirus could be released into the wild in Australia in as little as 5 years if some scientists and fisherfolk lobbyists could have their own way.

Carp are thought to be the reason for the rarity of native Australian fish because in some water bodies, as they can account for up to 90% of the biomass. But are they the pest that everyone makes them out to be? Are we blindly accepting this assumption that they have out competed the native fishes of their habitat and are destroying the environment? Is that finding a cause or effect? Are carp merely scapegoats to cover the fact that natural environmental changes (decreased rainfall) and human-related activities (diverting water for irrigating farms, damming, livestock damaging river banks, recreational activities, fertiliser, herbicide, pesticide and other chemical run-offs) may have caused significant changes to the aquatic environment that only the carp can survive and flourish under such conditions?

Any fish keeper can tell you that carp have soft lips and they are not territorial or aggressive. How then can they outcompete native Australian carnivorous fishes like the silver perch and Murray cod? These native fish are among the top predators and they are highly territorial and aggressive. What’s more is that they can eat carp for a meal. And how are carp more harmful to the environment than the non-native trout and salmon (again, top predators) that are regularly stocked in pristine rivers for the purposes of fishing? The fecundity of the carp would create a ready supply of food for the native fishes.

What could it mean for the fish in terms if animal welfare? What could it mean for non-target fish such as your beloved kois in your backyard? Will the government allow us to import the vaccine to protect our prized fish from certain death?

Could Australia find a use for this fish? Live export to improve genetic stocks in their native Europe? Sustainable food fish aquaculture for local consumption or export? Fertiliser? Coarse fishing?

Australia could remain the only place in the world with a carp population that is free from so many of the killer diseases. In terms of food security, should we be protecting the humble carp rather than release the killer virus amongst them?

Before releasing this KHV, I propose several ways of studying this phenomenon of high carp populations in certain water bodies to ascertain what is actually happening:

1. Conduct a full water quality analysis and compare this with historic data and with the respective fishes’ optimal ranges.

2. Different fish species can be grown in tanks utilising the waters from the water bodies to see if it had any impact on the health of the different fish species, measuring growth rate, reproductive ability, disease resistance, etc.

3. Several different fish species could be introduced into the different waterways and tracked to see how they fare.

Australia and its aquatic fauna should not become an experiment.

http://www.thefishvet.com.au

Apparently this disease can cripple a nation’s economy that is highly dependent on shrimp farming in as little as a week if the disease is allowed to spread. WSSV has low host specificity and can infect a large number of crustaceans. This paper illustrates several ecological ways of preventing WSSV outbreak.

Aquaculture
Volume 353, Number 11 (June 2012)
	Effect of three innovative culture systems on water quality and whitespot syndrome virus (WSSV) viral load in WSSV-fed Penaeus monodoncultured in indoor tanks
	Authors:	Eleonor A. Tendencia, Roel H. Bosma, Lynbelle Rose Sorio
	Author Affiliations:	no affiliations available
	Source:	Aquaculture, Volume 353, Number 11 (June 2012)
	Page Numbers:	169 – 174
	Available Full Text:	Full Text: Subscription Required to view full text Format: PDF Size: Unknown Location: Publisher’s Site Authentication: Publisher’s Site
	Abstract:	White spot syndrome virus is the most important among the shrimp diseases. It has been devastating the shrimp industry for more than 3 decades. Previous studies reported that greater percentage of yellow colonies on thiosulfate citrate bile salt sucrose agar (yellow vibrios) in the rearing water, abundant supply of natural food such as Chlorella, and the use of the greenwater technology (GW) are some ecological ways of preventing WSSV outbreak. The aim of this study was to investigate the efficiency of the 3 systems against WSSV.
	Citation:	Eleonor A. Tendencia, Roel H. Bosma, Lynbelle Rose Sorio . Effect of three innovative culture systems on water quality and whitespot syndrome virus (WSSV) viral load in WSSV-fed Penaeus monodoncultured in indoor tanks. Aquaculture, Volume 353, Number 11 (June 2012), pp. 169-174, <http://ejournals.ebsco.com/direct.asp?ArticleID=46FF946AFA99476D73BD&gt;
	URL:	http://ejournals.ebsco.com/direct.asp?ArticleID=46FF946AFA99476D73BD

Many involved with fish health know well that quarantine is the best policy where “An Ounce of Biosecurity…Worth More Than a Pound of Cure” (phrase borrowed from an up coming conference talk title – http://www.vet.purdue.edu/2012fallconference).

But have you thought about doing something different? One of my colleagues came up with a radically new, brilliant idea that would change the way we do things and save a lot of fish lives!

At the moment, ornamental fish imported into Australia are held in quarantine for 1, 2 or 3 weeks depending on the requirements. Fish in quarantine are not allowed to be treated with any medications so that no signs of disease will be masked.
If significant deaths do occur, the entire population in the affected tanks would have to be destroyed and/or a sample of the fish will need to be tested at the government laboratories. Moreover, the current method cannot detect asymptomatic carriers of diseases.

Because the ornamental fish sector has been highlighted as a threat to Australian biosecurity, there have been moves to tighten the quarantine rules. It has been proposed that 60 or 120 individuals per species batch will have to be sacrificed for destructive testing by local authorities.

This will mean that it will significantly increase the price for fishes and more importantly, unnecessary loss of the lives of thousands of fish. So, what is this radical new method that was suggested by my colleague?

We are aware that environmentalists study sentinel species to give an indication of the health of the environment. Miners in the past used canaries in coal-mines to provide an early indication of pending danger from gas accumulation.

My colleague proposed that we apply this same methodology of using biological indicators to demonstrate disease freedom of imported fish. Here, the quarantine setup will be designed such that water from the quarantine tanks are hooked up to tanks that house several fish species that are susceptible to the diseases we want to keep out (i.e. cohabiting with sentinels). If disease is present, the sentinel fishes would show signs of illness and they can be tested. If there is no disease, then the sentinel fishes will remain in good health and there is no needless destruction of fish. Some of the fish/disease pairings can include Murray cod for gourami iridovirus; fork tailed catfish or barramundi for Edwarsiella ictaluri.

But according to my colleague who proposed the idea, he says that it’s not a novel idea but is standard practice around the world in specific terresterial animal disease monitoring.

There have been several occasions where this method of quarantine would have proven useful for my clients where recently imported fish were carrying a particular strain of pathogen that their resident fish had no immunity to. The imported fish showed no signs of disease during quarantine in a separate pond, but when introduced to the main pond, the resident fish started dying in numbers.

The other brilliant aspect of this proposal is that I believe it will have a much higher rate of acceptance and hence adoption by the industry. Other things I’d add to make this work includes microchipping of the sentinel fishes and faster turnaround time for reporting laboratory results.

Worth a try in ornamental fish? Your thoughts?

http://www.thefishvet.com.au

Having dinner at a very fancy restaurant, the waiter asked the gentleman that was eating the fish,”How did you find the salmon?”

The puzzled guest looked at the plate and then again at the waiter and replied,”I moved the garnish aside and
voilà I found the fish!”

Check out the latest review for “Fish Vetting Essentials” in Veterinary Record. This is an established and well-regarded scientific journal with a worldwide distribution.

“it really is one of the most practical fish books I have come across and it is absolutely fascinating… given the unique qualities of this book, and its comprehensive yet practical coverage of fish medicine, I would strongly recommend it to anyone keen on seeing fish, whether experienced or just dabbling. And if you’re still not keen on taking the plunge, just find the number of the nearest aquarist and recommend they get a copy.”

More information about the book can be found by clicking on the following link:

Fish Vetting Essentials

Dr Loh has also published a second book.

Fish Vetting Medicines: Formulary of Fish Treatments

You can purchase these books at The Fish Vet’s site.

Please feel free to forward it to others who may be interested.

Thank you.

Book Review – Veterinary Record

I’ve seen several aquaponics setups that utilise the flood/drain method to water the plants, and hence act as the filtration for the fishes. I had always wondered whether there is enough filtration of the water for the health of the fish especially when the water runs only 4x per day.

This is why my DIY (do-it-yourself) backyard set up is a continuous flow method (nutrient film technique) utilising a submerged biofilter to filter the fishes’ wastes. I thought it’d be better for the fish to be in a proper aquaculture setup and then have the plants as an accessory. See Facebook fanpage link here.

This paper details the work done to come up with the conclusions that:

1. Removal of organic nitrogen and ammonia was higher in flood/drain biofilters.
2. Removal of nitrites and nitrates was better in submerged biofilters
3. The use of combined flood/drain and submerged biofilters may offer the best solution to the treatment of aquaculture waste.

Having said this, I’d like to do some water quality testing of my own for those with the flood/drain design, to look at TAN and nitrite levels.

Aquacultural Engineering
Volume 50, Number 2 (September 2012)
	Nitrogen removal and changes to microbial communities in model flood/drain and submerged biofilters treating aquaculture wastewater
	Authors:	Simon P. Gregory 1, Paul J. Dyson 2, David Fletcher 3, Philip Gatland 4, Robin J. Shields 1
	Author Affiliations:	1: Centre for Sustainable Aquatic Research, College of Science, Swansea University, Singleton Park, Swansea SA2 8PP, UK  2: Institute of Life Science, Swansea University, Singleton Park, Swansea SA2 8PP, UK  3: RAS Aquaculture Research Ltd, Pen Lon, Maes y Llan, Llandwrog, Gwynedd, UK  4: 31 Spindlewood, Brough, East Elloughton, HU15 1LL, UK
	Source:	Aquacultural Engineering, Volume 50, Number 2 (September 2012)
	Page Numbers:	37 – 45
	Available Full Text:	Full Text: Subscription Required to view full text Format: PDF Size: Unknown Location: Publisher’s Site Authentication: Publisher’s Site
	Abstract:	? Flood/drain biofilters were compared to submerged biofilters for the treatment of marine aquaculture wastewater. ? Analysis of 16s rRNA and amoAgenes by T-RFLP revealed distinct bacterial communities in the submerged and flood/drain biofilters. ? Removal of organic nitrogen and ammonia was higher in flood/drain biofilters. Removal of nitrites and nitrates was better in submerged biofilters. ? The use of combined flood/drain and submerged biofilters may offer the best solution to the treatment of aquaculture waste.
	Citation:	Simon P. Gregory, Paul J. Dyson, David Fletcher, Philip Gatland, Robin J. Shields . Nitrogen removal and changes to microbial communities in model flood/drain and submerged biofilters treating aquaculture wastewater. Aquacultural Engineering, Volume 50, Number 2 (September 2012), pp. 37-45, <http://ejournals.ebsco.com/direct.asp?ArticleID=41AF998AA0FB9C7061FB&gt;
	URL:	http://ejournals.ebsco.com/direct.asp?ArticleID=41AF998AA0FB9C7061FB