The Fish Vet's Blog

Fish density Is a very important factor when keeping fish together. Some schooling fish show preference and less stress when there is reduced ‘inter-fish’ distance. Another consideration for using stocking density is to reduce intra-specific aggression.

Aquaculture
Volume 323, Number 1 (December 2011)
	Social, stocking density and dietary effects on the failure of farmed cod Gadus morhua
	Authors:	James Treasurer, Tim Atack, Anne Rolton, Jamie Walton, Ralph Bickerdike
	Author Affiliations:	no affiliations available
	Source:	Aquaculture, Volume 323, Number 1 (December 2011)
	Page Numbers:	241 – 248
	Available Full Text:	Full Text: Subscription Required to view full text Format: PDF Size: Unknown Location: Publisher’s Site Authentication: Publisher’s Site
	Abstract:	A large proportion of cod juveniles fail following transfer to sea cages from the hatchery. Failed cod take and then eject feed and are thin and emaciated fish of low weight compared with “normal” siblings. Failed fish comprised 70% of total mortalities and 10% of fish stocked in the first eight months of production on a cod farm in Scotland. Failed cod comprised from 0 to 8% of fish reared in twelve hatchery tanks over 3months. These failed cod were graded from larger fish in five consecutive grades at four to six weekly intervals and, after being reared separately, over 90% of these fish were “recovered”. No significant differences were found in food acceptance of six alternative diets and a standard marine commercial diet by failed cod. Smaller pellets or feed moistened in seawater were offered but this did not significantly increase the rate of feed acceptance. The effects of stocking density on the development of failed cod were assessed by comparing performance at densities of 0.2, 2 and 20kgm-3. Aggressive interaction was lowest at an intermediate stocking density of 2kgm-3and highest at a density of 20kgm-3. Fin nipping was concentrated on the first dorsal fin and was not significantly different between stocking densities, but the other dorsal fins, pectoral fins and tail were also attacked more frequently at the highest stocking density. It is concluded that failed cod can be recovered by grading from the main population and feeding these cod separately. Stocking densities in sea cages should initially be similar to hatchery levels and this may be achieved by holding the cod in small enclosures within the main net.
	Citation:	James Treasurer, Tim Atack, Anne Rolton, Jamie Walton, Ralph Bickerdike . Social, stocking density and dietary effects on the failure of farmed cod Gadus morhua. Aquaculture, Volume 323, Number 1 (December 2011), pp. 241-248,
	URL:	http://ejournals.ebsco.com/direct.asp?ArticleID=48AC8C7D9ACB29C7E202

Integrated aquaculture systems is the fad at the moment, and I think it’s the only sustainable way of culturing. Very common traditional methods were pioneered by China with their chicken coups placed above fish ponds to fertilise the water body which allows vegetation to grow and feed the fish.

The more modern, intensive version is known as Aquaponics – what some of us dabble in our backyards. It is a combination of aquaculture (most commonly, edible fish) and Aquaponics (most commonly, edible vegetables).

This paper reports findings on integrating prawn farming with seaweed culture.

Aquaculture
Volume 323, Number 1 (December 2011)
	Integration of western king prawn (Penaeus latisulcatusKishinouye, 1896) and green seaweed (Ulva lactucaLinnaeus, 1753) in a closed recirculating aquaculture system
	Authors:	Le Van Khoi, Ravi Fotedar
	Author Affiliations:	no affiliations available
	Source:	Aquaculture, Volume 323, Number 1 (December 2011)
	Page Numbers:	201 – 209
	Available Full Text:	Full Text: Subscription Required to view full text Format: PDF Size: Unknown Location: Publisher’s Site Authentication: Publisher’s Site
	Abstract:	Integrating recirculating aquaculture systems with seaweeds is one of the strategies that can minimise wastes and risk of disease outbreaks. This study investigated the effect of integrating green seaweed (Ulva lactuca) with western king prawns (Penaeus latisulcatus) at varying stocking densities on the water quality, nutrient conversion rates and nutrient budget under closed recirculating culture system. The experiment was conducted using fifteen indoor tank recirculating systems and tested four different stocking ratios of prawns and seaweed with a control having prawns only. The four stocking ratios of seaweed and prawn biomass were 2, 4, 8 and 16 per tank. The mean concentrations of total ammonia nitrogen (TAN), NO3-–N and PO43-–P in the prawn and seaweed tanks were significantly lower (P<0.05) in the integrated culture systems than in the prawn monoculture. U. lactucawas highly efficient in removing the inorganic nutrients from the culture systems with TAN removal rate of 59–81% and PO43-–P removal rate of 50–55%. Integrating seaweed with prawns did not significantly alter the specific growth rate (SGR) and survival rate of the prawns (P0.05). Ratio of C:P in seaweed tissues decreased with increasing seaweed stocking densities while C:N ratio showed an adverse trend. The nutrient conversion rate into total biomass (prawns plus seaweed) in the integrated systems was significantly higher at the highest seaweed stocking density (2.00kgm-2). Nutrient budget revealed that seaweed retained about 6.5–29.7% nitrogen and 1.6–13.5% phosphorus inputs while values for prawns were 28.0–31.9% and 13.5–14.6%, respectively. Seaweed also removed dissolved inorganic nitrogen effectively in the closed recirculating aquaculture system.
	Citation:	Le Van Khoi, Ravi Fotedar . Integration of western king prawn (Penaeus latisulcatusKishinouye, 1896) and green seaweed (Ulva lactucaLinnaeus, 1753) in a closed recirculating aquaculture system. Aquaculture, Volume 323, Number 1 (December 2011), pp. 201-209,
	URL:	http://ejournals.ebsco.com/direct.asp?ArticleID=41A9A015DF0E15F5AA6D

I was listening to the radio this evening and they were talking about animal trivia. I couldn’t help but to think up of so many fallacies that have been circulated time and time again.

Do you know what a pregnant goldfish is called? Some would try to make you believe that a pregnant goldfish is called a twit, or a twerp.

In reality there is no term for a pregnant goldfish because goldfish never get pregnant! Female Goldfish lay eggs and the eggs are fertilised by male fish outside of the body.

There are however, some fishes that do get pregnant such as guppies, mollies, platies and some sharks!

I am in the midst of constructing an Aquaponics system in my backyard… I wonder if I need to paint all my tanks.

Aquaculture
Volume 323, Number 1 (December 2011)
	Tank color increases growth, and alters color preference and spectral sensitivity, in barramundi (Lates calcarifer)
	Authors:	Jeremy F.P. Ullmann, Tom Gallagher, Nathan S. Hart, Andrew C. Barnes, Richard P. Smullen, Shaun P. Collin, Shelby E. Temple
	Author Affiliations:	no affiliations available
	Source:	Aquaculture, Volume 323, Number 1 (December 2011)
	Page Numbers:	235 – 240
	Available Full Text:	Full Text: Subscription Required to view full text Format: PDF Size: Unknown Location: Publisher’s Site Authentication: Publisher’s Site
	Abstract:	This study investigated the effects of four different colored environments on the color preference, spectral sensitivity, and growth of juvenile barramundi, Lates calcarifer. Barramundi were reared for 9 weeks in one of four colored aquaria (blue, red, yellow, and green) after which their spectral sensitivities, color preference and growth were determined. Prior to the commencement of the experiment barramundi were found to possess four morphologically and physiologically different photoreceptors in their retina with ?maxvalues of cones at 472±6nm, 580±10nm, 595±10nm, and rods at 516±8nm, and they showed an inherent color preference for blue and green. At the completion of the experiment, statistical differences were seen in growth, as barramundi from red aquaria were larger than fish from green and blue aquaria (p<0.05). Spectral sensitivity results were similar to growth as barramundi from all four colored aquaria shifted the spectral absorbance of their photoreceptors towards longer wavelengths (p<0.05). Finally, barramundi color preference also changed, as fish reared in red tanks had a trend to spend less time in red and yellow quadrants. These results indicate that the effects of the ambient light environment are not straightforward and analyses of the visual system and behavior may be instrumental for improving growth rates in farmed fish.
	Citation:	Jeremy F.P. Ullmann, Tom Gallagher, Nathan S. Hart, Andrew C. Barnes, Richard P. Smullen, Shaun P. Collin, Shelby E. Temple . Tank color increases growth, and alters color preference and spectral sensitivity, in barramundi (Lates calcarifer). Aquaculture, Volume 323, Number 1 (December 2011), pp. 235-240,
	URL:	http://ejournals.ebsco.com/direct.asp?ArticleID=449382AE3E97DB7C5093

Dr Loh will be working at Boronia Aquarium today.

Routine work during the monthly trips ensure the fishes are vet checked and treated for any ailments in order to provide Boronia Aquarium’s customers with healthy fish.

You can visit me at Boronia Aquarium today or check http://www.boroniaaquarium.com.au

> Environment Agency race to save hundreds of trapped salmon after 2,000 mile journey > http://www.fishupdate.com/news/fullstory.php/aid/16679
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> Hundreds of salmon and trout unable to reach their spawning grounds due to low water levels in the River Teme at Ludlow have successfully begun migrating upstream, thanks to swift river modifications by the Environment Agency. >
> More than 200 fish on their way to spawning grounds became trapped between two weirs on the River Teme earlier this week. >
> The fish had travelled 2,000 miles across the sea and up river to spawn, but became weak as they neared the end of their journey. >
> The salmon also became a sitting target for local poachers and the Environment Agency had to set up a 24-hour guard to prevent the fish being taken. >
> In order to get the tired fish over the weir, the Environment Agency created a temporary fish pass corridor for the stranded salmon. This involved knocking the top off a section of the weir with a pneumatic chisel to lower it’s height, and creating a graduated ramp to allow fish to move up to the top of the weir more easily. >
> The salmon are very sensitive to disturbance and could not be rescued with nets, as the stress would have killed them. >
> The Environment Agency’s Head of Water Resources, Trevor Bishop, said some areas of the country have seen the driest 12 months since records began, affecting wildlife. >
> “The Environment Agency’s job is to balance the water needs of people, business and environment and we are continuing to monitor and manage the consequences of ongoing dry weather. >
> “We are taking prompt action to minimise the impacts of drought, such as fish rescues, and we are glad to have successfully helped the tired salmon and trout on their way.” >
>

Nitrate is not as benign as often thought.

Aquaculture
Volume 323, Number 1 (December 2011)
	Acute exposure of juvenile cobia Rachycentron canadum to nitrate induces gill, esophageal and brain damage
	Authors:	Ricardo V. Rodrigues, Michael H. Schwarz, Brendan C. Delbos, Eduardo L. Carvalho, Luis A. Romano, Luís A. Sampaio
	Author Affiliations:	no affiliations available
	Source:	Aquaculture, Volume 323, Number 1 (December 2011)
	Page Numbers:	223 – 226
	Available Full Text:	Full Text: Subscription Required to view full text Format: PDF Size: Unknown Location: Publisher’s Site Authentication: Publisher’s Site
	Abstract:	Cobia Rachycentron canadumis a fast growing fish with world-wide potential for aquaculture, and has been considered for rearing in recirculating aquaculture systems (RAS). Nitrate is considered the least toxic nitrogenous product in the ammonia nitrification process, but as it may accumulate in RAS, toxic levels can be reached. The objective of this study was to evaluate the acute toxicity and the histopathological effects of nitrate on juvenile cobia. Juveniles (6.87±0.36g; 11.8±0.19cm) were acutely exposed to six concentrations of nitrate (500–3000ppm NO3–N) plus a control during 96h. At the end of this period of exposure, juvenile cobia were sampled for histopathological evaluation. The estimated LC50of nitrate to juvenile cobia was equal to 2407 and 1829mg/L NO3–N at 24 and 96h, respectively. Cobia exposed to sub-lethal nitrate concentrations showed histopathologic alterations in the gills, esophagus and brain. The gills revealed epithelial hyperplasia with complete lamellar fusion, telangiectasia, and lamellar shorting induced by necrosis, and the esophagus presented hyperplasia of epithelium and mucus cells. In the brain, glial cells proliferation, satellitosis (microglial cells surrounding neurons with swollen and prenecrotic neurons), and Virchow-Robin spaces (enlarged perivascular spaces, EPVS) were observed. The results of the present study indicate that juvenile cobia have a high tolerance to acute exposure of nitrate. However, assorted histopathological responses were observed for cobia at sub-lethal nitrate concentrations. Therefore, further studies are needed to estimate safe chronic nitrate levels for juvenile cobia culture.
	Citation:	Ricardo V. Rodrigues, Michael H. Schwarz, Brendan C. Delbos, Eduardo L. Carvalho, Luis A. Romano, Luís A. Sampaio . Acute exposure of juvenile cobia Rachycentron canadumto nitrate induces gill, esophageal and brain damage. Aquaculture, Volume 323, Number 1 (December 2011), pp. 223-226,
	URL:	http://ejournals.ebsco.com/direct.asp?ArticleID=4426B202E35D90059EF8

Dear Fish Fans,

As you know, the initial print run of this book sold out very quickly. Another print run was requested and are due to arrive early next week.

In another note, I have had a few requests to autograph the book. So, for the month of December, you can request to have your copy personally autographed. Just detail in the ‘notes’ section your preferences.

You can place an order for your copy via my website’s shopping cart.
http://thefishvet.com.au/shop/shopping.html

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

Is microwaved food better for fish? Read on…

Aquaculture
Volume 323, Number 1 (December 2011)
	Effects of different modified diets on growth, digestive enzyme activities and muscle compositions in juvenile Siamese fighting fish (Betta splendensRegan, 1910)
	Authors:	Karun Thongprajukaew, Uthaiwan Kovitvadhi, Satit Kovitvadhi, Pisamai Somsueb, Krisna Rungruangsak-Torrissen
	Author Affiliations:	no affiliations available
	Source:	Aquaculture, Volume 323, Number 1 (December 2011)
	Page Numbers:	1 – 9
	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 four modified diets (gamma-irradiated, microwave-irradiated, probiotic-supplemented and carbohydrase-supplemented diets) were studied on digestive enzyme specific activities and growth performance quality of juvenile Siamese fighting fish (Betta splendensRegan, 1910) during 2weeks of critical and intensive rearing period. The modified procedures did not change biochemical compositions and gross energy of diets, but generally resulted in relatively higher in vitro digestibilities of protein and carbohydrate and fish survival rate, albeit insignificant. Only gamma irradiation significantly increased in vitro protein digestibility of the diet, and microwave irradiation increased starch gelatinization and water solubility (P<0.05). Fish fed microwave-treated diet showed highest values in all studied growth indicators and digestive enzyme specific activities (except lipase), with significantly higher amylase specific activity and activity ratio of amylase to trypsin (A/T ratio). Correlation analysis indicated significant relationships (P<0.05) among the levels of total protease, amylase and trypsin, and between SGR and A/T ratio. Muscle and body compositions of juveniles fed on microwave- or gamma-irradiated diets were similar to the control, while the juveniles fed on probiotic- or carbohydrase-supplemented diets showed lower protein depositions (P<0.05). Similar levels of RNA, RNA/Protein ratio, and Protein/Lipid ratio in body and muscle in all dietary groups fed ad libitum suggested that the improved growth performance in juvenile Siamese fighting fish fed on microwave-irradiated diet may not be only due to improved physicochemical properties of the diet but also improved fish consumption rate.
	Citation:	Karun Thongprajukaew, Uthaiwan Kovitvadhi, Satit Kovitvadhi, Pisamai Somsueb, Krisna Rungruangsak-Torrissen . Effects of different modified diets on growth, digestive enzyme activities and muscle compositions in juvenile Siamese fighting fish (Betta splendensRegan, 1910). Aquaculture, Volume 323, Number 1 (December 2011), pp. 1-9,
	URL:	http://ejournals.ebsco.com/direct.asp?ArticleID=4C9CB23C157255C4F6CC