Several water quality parameters fluctuate throughout the day. Dissolved oxygen is no exception, especially in planted or green ponds. On several occasions, my clients have told me that they run their pumps during the day and then turn their pumps off in the evening. I told them that in fact, it is actually more useful to turn their pumps on during the night than during the day because the plants only photosynthesize during the day. Of course, the pumps should be turned on continuously if it is used to operate a biological filter.

In extensive pond culture, you may notice that paddlewheel aerators are situated in strategic locations instead of water pumps or air pumps as they consume less energy. The other benefit of paddlewheel aerators is that through the water movement created, they can also direct wastes towards a section of the pond. I have diverged.

Anyway, it is important to maintain a minimum dissolved oxygen level at all times for improved productivity as evidenced in this paper.

Aquaculture
Volume 353, Number 11 (June 2012)
	Response of channel×blue hybrid catfish to chronic diurnal hypoxia
	Authors:	Bartholomew W. Green, Steven D. Rawles, Benjamin H. Beck
	Author Affiliations:	no affiliations available
	Source:	Aquaculture, Volume 353, Number 11 (June 2012)
	Page Numbers:	183 – 191
	Available Full Text:	Full Text: Subscription Required to view full text Format: PDF Size: Unknown Location: Publisher’s Site Authentication: Publisher’s Site
	Abstract:	Performance traits and metabolic responses of the channel×blue hybrid catfish (Ictalurus punctatusfemale×I. furcatusmale) in response to chronic diurnal hypoxia were evaluated in this 197-d study. Sixteen 0.1-ha earthen ponds were stocked with 15,169 hybrid catfish/ha (47g/fish) and managed to maintain the minimum dissolved oxygen concentration greater than 12%, 24%, 36%, or 48% of saturation. Growth and yield of channel×blue hybrid catfish were significantly related to minimum nightly dissolved oxygen concentration. The cumulative effect of nocturnal dissolved oxygen concentration and the duration of exposure to hypoxia (termed dissolved oxygen-minutes) proved to be a better independent variable for regression analysis than minimum nightly dissolved oxygen concentration. Gross and net yield and mean individual weight increased curvilinearly as dissolved oxygen-minutes increased. Chronic nightly hypoxia affected daily feed consumption and channel×blue hybrid catfish in the higher dissolved oxygen treatments grew faster because they consumed a greater percentage of their body weight at each feeding. Feed consumption increased linearly in response to dissolved oxygen-minutes during the peak production period (June–August), but curvilinearly over the entire study. Body compositional indices largely were unaffected by chronic nightly hypoxia. Lipid was the primary depot affected by hypoxia and lipid indices increased with increasing dissolved oxygen concentration and with increasing total feed fed. Citrate synthase activity was 14.6% higher in the highest compared to the lowest dissolved oxygen treatment and a strong inverse relationship between citrate synthase activity and fish body mass was observed in the highest dissolved oxygen concentration treatment. Results of this study suggest that pond dissolved oxygen concentration should be maintained at 48% saturation during the peak production period (water temperatures above 25C) and at 36% saturation during the rest of the growing season.
	Citation:	Bartholomew W. Green, Steven D. Rawles, Benjamin H. Beck . Response of channel×blue hybrid catfish to chronic diurnal hypoxia. Aquaculture, Volume 353, Number 11 (June 2012), pp. 183-191, <http://ejournals.ebsco.com/direct.asp?ArticleID=49B4AC2A2A556BCCF5BD&gt;
	URL:	http://ejournals.ebsco.com/direct.asp?ArticleID=49B4AC2A2A556BCCF5BD

 
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Aquaculture plays a “critical role for aquaculture in feeding the world, stimulating economic development, providing employment and reducing existing negative impacts on the marine environment.”

Talks about co-location with other off-shore ventures, new net-pen technology and more…

http://www.fishupdate.com/m/fullstory.php/aid/18454/Offshore_mariculture_industry_looks_to_high_seas_opportunities.html

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Yours sincerely,

Dr Richmond Loh
BSc BVMS MPhil MANZCVS (Aq & Pathol)
The Fish Vet, Perth, Western Australia.
Veterinary Medicine for fish.
http://www.thefishvet.com.au
Ph: +61 (0)421 822 383

A mix of foods seems the best. See latest research article below.

Aquaculture Research
Volume 43, Number 12 (November 2012)
	Feeding selectivity of the seahorse, Hippocampus kuda(Bleeker), juveniles under laboratory conditions
	Authors:	Fritzie T Celino, Grace V Hilomen-Garcia, Annabelle G C del Norte-Campos
	Author Affiliations:	no affiliations available
	Source:	Aquaculture Research, Volume 43, Number 12 (November 2012)
	Page Numbers:	1804 – 1815
	Available Full Text:	Full Text: Subscription Required to view full text Format: PDF Size: unknown Location: Publisher’s Site Authentication: EBSCOhost EJS
	Abstract:	This study examined the feeding selectivity of Hippocampus kuda juveniles under captive conditions and evaluates different food organisms that could be used to improve hatchery-rearing of this species. Newly born H. kuda were reared for 10 days in 60-L capacity tanks and fed rotifers (Brachionus rotundiformis), zooplankton (mostly Pseudodiaptomus annandalei and Acartia tsuensis) alone or both food sources. The size and amount of food ingested increased as seahorses grew. Selective feeding of seahorses appeared to change as they develop, preferring copepod adults over nauplii and rotifers. A. tsuensis was highly selected by juveniles over P. annandalei. Specific growth rate in terms of body weight (SGR-BW, 15% day–1) was the highest and mortality rate (9% at day 10) the lowest in seahorses fed a mixed food sources. Slowest growth rate (0.3% day–1) and highest mortality rate (60% at day 7) were observed in seahorses fed rotifers alone. These results indicate that copepods are suitable food for seahorse juveniles, but a mixture of food organisms in the rearing tank environment enhances survivorship and growth of H. kuda, thus potentially providing a source of cultured rather than wild specimens for characterizing the life history of this threatened species.
	Citation:	Fritzie T Celino, Grace V Hilomen-Garcia, Annabelle G C del Norte-Campos . Feeding selectivity of the seahorse, Hippocampus kuda(Bleeker), juveniles under laboratory conditions. Aquaculture Research, Volume 43, Number 12 (November 2012), pp. 1804-1815, <http://ejournals.ebsco.com/direct.asp?ArticleID=463A8F2B4B9DA9B5A9E9&gt;
	URL:	http://ejournals.ebsco.com/direct.asp?ArticleID=463A8F2B4B9DA9B5A9E9

Did you know that along with my YouTube channel (thefishvetdrloh), I have included the most useful ones on my website under the pictures/videos section?

Follow this link to bring you straight there –

http://thefishvet.com.au/videos.html

It took me two weeks of giving this work experience student the guilt trip before he finally LIKED my Facebook Fanpage!

SUCCESS !!!!

So, if you haven’t already done so, please do like what I’ve coined, my Facebook Fin-page!

www.facebook.com/thefishvetdrloh

Did you know that barramundi start as males and then as they get bigger, turn into females (the feminists may say,”Mature into females!”)?

The reverse is true in wrasses. The fish that live in small groups start off as females and the largest, most mature fish becomes the male. This male guards their territory and his harem. If the male meets his demise, then the next largest fish (a female) will turn into the new male fish!

Of the popular aquarium fishes, some say that some of the female swordtail fish can turn into males, developing the long caudal fin extension and modification of the anal fin to form the gonopodium.

These are just a few examples of the sex changing fishes out there.

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This recent research shows it takes on average, up to 8 years for farmers to get a return on investment. So, it really does pay to get it right, right from the start… as this paper reports.

Aquacultural Engineering
Volume 51, Number 11 (November 2012)
	Recirculating Aquaculture Systems (RAS) analysis: Main issues on management and future challenges
	Authors:	Maddi Badiola 1, Diego Mendiola 1, John Bostock 2
	Author Affiliations:	1: AZTI-Tecnalia, Marine Research Division, Herrera Kaia, Portualdea s/n, 20110 Pasaia, Spain 2: Institute of Aquaculture, University of Stirling, Stirling FK9 4LA, UK
	Source:	Aquacultural Engineering, Volume 51, Number 11 (November 2012)
	Page Numbers:	26 – 35
	Available Full Text:	Full Text: Subscription Required to view full text Format: PDF Size: Unknown Location: Publisher’s Site Authentication: Publisher’s Site
	Abstract:	? RAS companies, researchers and consultants all over the world were surveyed. ? Poor system designs, water quality issues and mechanical problems are the main constraints. ? 50% of the surveyed companies have been rebuilt or redesigned due to RAS system’s failure. ? More than 8 years are needed to get back initial investment. ? In the future, information platforms, their availability and specialized education will be required.
	Citation:	Maddi Badiola, Diego Mendiola, John Bostock . Recirculating Aquaculture Systems (RAS) analysis: Main issues on management and future challenges. Aquacultural Engineering, Volume 51, Number 11 (November 2012), pp. 26-35, <http://ejournals.ebsco.com/direct.asp?ArticleID=49E28942163732A24E42&gt;
	URL:	http://ejournals.ebsco.com/direct.asp?ArticleID=49E28942163732A24E42

 
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The topic of what’s the best antibiotics has been rather popular on my blog and also a topic of great interest at my recent presentation to the Koi Society of WA on treating fish with ulcers. So, I think this might be a good time to resurrect one of my old YouTube clips that’s pertinent to the topic.

Sentinel species are used to inform us about environmental processes that are too difficult or too expensive to measure directly. In conservation biology, an ideal sentinel species is a large-bodied, wide-ranging creature occupying top positions in local food webs.

Historically sentinel species were used on a presence-absence basis, much like a canary in a coal mine. Unfortunately, by the time such a sentinel vanished to indicate that a habitat was deteriorating, it was too late to save what remained.

In the aquatic realm, a different choice of species would be more appropriate so that we can detect when habitats are becoming degraded long before the top predator species disappears; when there is still plenty of time to work with local wildlife managers to save these habitats.

 
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