The Fish Vet's Blog

Air exposure and mechanical agitation are commonly used methods for decreasing shell biofouling in the shellfish industry. However, these techniques cause significant stress to the bivalves. Could these anthropomorphic measures have contributed to the major decline of the Australian pearl oyster industry (see tech notes on Oyster Oedema Disease)? Some food for thought.

Aquaculture
Volume 363, Number 8 (September 2012)
	Changes in the transcriptional expression of oxidative stress response genes in Akoya pearl oysters (Pinctada fucata) exposed to air and mechanical agitation
	Authors:	Rhiannon P. Kuchel, Sham Nair, David A. Raftos
	Author Affiliations:	no affiliations available
	Source:	Aquaculture, Volume 363, Number 8 (September 2012)
	Page Numbers:	33 – 38
	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 Akoya pearl oyster is an economically important species farmed throughout Japan and China, and on a small scale in Australia. Recent proliferation of Akoya viral disease (AVD) has dramatically reduced both wild and farmed populations in Asia. It is thought that AVD is exacerbated by anthropogenic pressures associated with over-crowding and stress caused by fluctuations in the environment, as well as by husbandry and handling. To test the effects of these stressors, the differential expression of genes encoding three antioxidant enzymes (peroxiredoxin, PRx; glutathione-S-transferase, GST; glutathione peroxidase, GPx) and the generic stress biomarker heat shock protein 70 (HSP-70) was investigated using quantitative real-time PCR on mRNA extracted from gill tissues of Pinctada fucatathat had been exposed to either mechanical agitation (MA, a combination of air exposure and shaking) or air alone for 1h and 6h. We observed a significant decline (up to 50%; p<0.05) in the expression of both GST and PRx 60min after oysters were exposed to air and MA. GPx transcription declined significantly 60min after exposure to MA. Hierarchical cluster analysis and multidimensional scaling (MDS) demonstrated that, even though no significant differences were identified in the expression of these genes 6h after exposure to stress, there was still a clear differentiation between controls and the two stress treatments. After 6h, the MDS analysis showed that antioxidant enzyme expression was intermediate between the 60min time point and the non-stressed controls. The MDS plot also demonstrated that there was no clear distinction between exposure to air and MA, suggesting that air exposure (which was a component of both treatments) is the main causative agent of transcriptional stress responses. HSP-70 expression also declined when oysters were exposed to both stressors, but these decreases were not statistically significant. Overall, the data suggest that the antioxidant systems of oysters are affected by exposure to air. This contributes to a growing understanding of short-term stress responses in bivalve molluscs and their potential effects on cellular homeostasis.
	Citation:	Rhiannon P. Kuchel, Sham Nair, David A. Raftos . Changes in the transcriptional expression of oxidative stress response genes in Akoya pearl oysters (Pinctada fucata) exposed to air and mechanical agitation. Aquaculture, Volume 363, Number 8 (September 2012), pp. 33-38, <http://ejournals.ebsco.com/direct.asp?ArticleID=4BA7B78B31C5AA067019&gt;
	URL:	http://ejournals.ebsco.com/direct.asp?ArticleID=4BA7B78B31C5AA067019

I received some interesting anecdotal comments on my previous blog (www.thefishvet.com) via LinkedIn and would like to share with you.

More on the war against the crown of thorns.

http://mobile.news.com.au/travel/news/eureka-moment-in-starfish-fight/story-e6frfq80-1226490688221

http://www.abc.net.au/news/2012-10-08/scientists-inject-bovril-like-hope-into-reef-starfish-fight/4300530

What do you call a pregnant goldfish?

You don’t call it anything because goldfish do not get pregnant! They are egg scatterers and fertilisation occurs outside of the body. Fish that are very full of eggs can be called “gravid”.

A lot of mumbo jumbo for those uninitiated in science speak, but the summary is that there are hormonal changes help them to very efficiently convert everything they eat into growth during the spring/summer period.

Aquaculture
Volume 363, Number 8 (September 2012)
	Growth, osmoregulation and endocrine changes in wild Atlantic salmon smolts and post-smolts during marine migration
	Authors:	Sigurd O. Stefansson, Monika Haugland, Björn Thrandur Björnsson, Stephen D. McCormick, Marianne Holm, Lars O.E. Ebbesson, Jens Chr. Holst, Tom O. Nilsen
	Author Affiliations:	no affiliations available
	Source:	Aquaculture, Volume 363, Number 8 (September 2012)
	Page Numbers:	127 – 136
	Available Full Text:	Full Text: Subscription Required to view full text Format: PDF Size: Unknown Location: Publisher’s Site Authentication: Publisher’s Site
	Abstract:	We have examined physiological parameters associated with seawater adaptability, growth and energetics, as well as major endocrine regulators of these processes in wild migrating Atlantic salmon smolts and post-smolts from the river through the fjord, coastal areas and the open ocean. Muscle RNA/DNA ratio suggests that growth rate increases soon after entry into seawater and continues to increase after the post-smolts reach the offshore banks and the feeding grounds in the Norwegian Sea. Post-smolts prioritize rapid growth and protein deposition in spring and summer, and their energy intake during this period is so high that deposition of energy is possible in addition to muscle growth. An increase in thyroxine (T4) and triiodothyronine (T3) levels was observed, suggesting a major activation of hepatic conversion of T4to T3in post-smolts in seawater, probably related to the high metabolic activity and rapid growth and development of the post-smolts. Decreased plasma growth hormone (GH) levels were observed from the river through the fjord, with levels around 2ngml-1in rapidly growing post-smolts, concurrent with an increase in circulating insulin-like growth factor I (IGF-I). An increase in pituitary GH expression levels and hepatic GH receptor (GH-R) and local IGF-I mRNA levels suggest a physiological basis for the changes in circulating GH and IGF-I levels. Receptor expression in brain and pituitary suggests that both hormones are actively involved in the growth and differentiation of these tissues during the critical early marine phase. Gill Na+,K+-ATPase (NKA) activity increased to post-smolt levels above 20µmol ADP mgprot.÷1h÷1, probably representing long-term NKA activity levels of Atlantic salmon in seawater. Concurrent with the changes in NKA activity the expression of the NKA a1b isoform remained high in post-smolts, while the expression of the NKA a1a decreased from smolts to post-smolts. Both cystic fibrosis transmembrane conductance regulator (CFTR) I and II showed a reduction in mRNA levels from smolts to post-smolts, and remained stable at low expression levels in seawater.
	Citation:	Sigurd O. Stefansson, Monika Haugland, Björn Thrandur Björnsson, Stephen D. McCormick, Marianne Holm, Lars O.E. Ebbesson, Jens Chr. Holst, Tom O. Nilsen . Growth, osmoregulation and endocrine changes in wild Atlantic salmon smolts and post-smolts during marine migration. Aquaculture, Volume 363, Number 8 (September 2012), pp. 127-136, <http://ejournals.ebsco.com/direct.asp?ArticleID=4BB787BD8A151B2092BC&gt;
	URL:	http://ejournals.ebsco.com/direct.asp?ArticleID=4BB787BD8A151B2092BC

Anyone who has cultured or kept crustacea will know that the animals seem to “grow” much larger after immediately after moulting and nothing much seems to happen in between. This clever experiment demonstrates how different coloured lights can play a role in growth rates and moulting frequency. Such experimentation will become more practical if/when shrimp culture migrates to the predicted “super-intensive” systems.

Aquaculture
Volume 363, Number 8 (September 2012)
	Effect of periodic light color change on the molting frequency and growth of Litopenaeus vannamei
	Authors:	Biao Guo, Yingchun Mu, Fang Wang, Shuanglin Dong
	Author Affiliations:	no affiliations available
	Source:	Aquaculture, Volume 363, Number 8 (September 2012)
	Page Numbers:	67 – 71
	Available Full Text:	Full Text: Subscription Required to view full text Format: PDF Size: Unknown Location: Publisher’s Site Authentication: Publisher’s Site
	Abstract:	Six color treatments Yellow light (Y), Green light (G), Blue light (B), Blue light to Yellow light (BY), Blue light to Green light (BG), Green to Yellow light (GY) were tested to determine if light color change can promote the growth of Litopenaeus vannamai. After a 45-day experiment, shrimp in BG treatment showed the best weight gain (WG) and the specific growth rate (SGRd), which might have been caused by high food conversion efficiency (FCEd), lowest energy allocation for respiration and highest energy allocation for growth. The molting frequency in GY treatment was the highest, but the growth was not the best. These results suggest that the periodic fluctuation from blue region of the spectrum to green region of the spectrum could promote the growth of L. vannameiand this periodic light color fluctuation may be used as a pattern of regulation of light color in the commercial shrimp culture.
	Citation:	Biao Guo, Yingchun Mu, Fang Wang, Shuanglin Dong . Effect of periodic light color change on the molting frequency and growth of Litopenaeus vannamei. Aquaculture, Volume 363, Number 8 (September 2012), pp. 67-71, <http://ejournals.ebsco.com/direct.asp?ArticleID=4CD28768DFA6A9DD42E9&gt;
	URL:	http://ejournals.ebsco.com/direct.asp?ArticleID=4CD28768DFA6A9DD42E9

Sent in by my friend, Yancey, via Facebook.

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A novel approach to monitor fish health in fish farms is proposed in this study.

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Aquaculture International: Journal of the European Aquaculture Society
Volume 20, Number 5 (October 2012)
	Development of a novel histopathological gill scoring protocol for assessment of gill health during a longitudinal study in marine-farmed Atlantic salmon (Salmo salar)
	Authors:	Susan Mitchell, Emily Baxter, Celia Holland 1, Hamish Rodger 2
	Author Affiliations:	1: Department of Zoology, School of Natural Sciences, Trinity College Dublin, Dublin, Ireland 2: Vet-Aqua International, Oranmore Business Park, Oranmore, Co. Galway, Ireland
	Source:	Aquaculture International: Journal of the European Aquaculture Society, Volume 20, Number 5 (October 2012)
	Page Numbers:	813 – 825
	Available Full Text:	Full Text: Subscription Required to view full text Format: PDF Size: unknown Location: Publisher’s Site Authentication: EBSCOhost EJS
	Abstract:	Abstract Gill health and disease in farmed Atlantic salmon (Salmo salar) were studied at a marine site on the west coast of Ireland. Fish were sampled on a regular basis during the summer and autumn of 2009. A novel histopathological scoring system was devised to give a semi-quantitative measure of gill pathology. The index criteria for gill histopathology were lamellar hyperplasia, lamellar fusion, circular anomalies (necrosis or sloughing) and lamellar oedema, a score from 0 to 3 being assigned for each parameter. Ancillary criteria, such as hypertrophy, haemorrhage and the presence of specific pathogens, were assigned a score of 0 or 1. Environmental monitoring undertaken included zooplankton and phytoplankton sampling, as well as temperature and oxygen recordings for the site. Epitheliocystis was frequently observed at low levels but was not associated with any significant gill pathology. Clinically significant gill pathology was observed on one occasion during the sampling period, coinciding with the occurrence of Pelagia noctiluca, Muggiaea atlantica and Solmaris corona. Throughout the longitudinal study, the scoring system provided an accurate and effective means of assessing gill health, demonstrating the ability of this practical tool to be used in future studies of gill health and disease.
	Citation:	Susan Mitchell, Emily Baxter, Celia Holland, Hamish Rodger . Development of a novel histopathological gill scoring protocol for assessment of gill health during a longitudinal study in marine-farmed Atlantic salmon (Salmo salar). Aquaculture International: Journal of the European Aquaculture Society, Volume 20, Number 5 (October 2012), pp. 813-825, ;
	URL:	http://ejournals.ebsco.com/direct.asp?ArticleID=40A1A28A3F7E34A78647

Pelvic fins are the paired find that appear on the ventral aspect of many fishes. They’re mainly used as a rudder to help steer the fish.

Some fish such as the female Corydoras use them to cup the eggs they have just laid, holding them in position until they get milt from the males to fertilise them.

Some fish such as the gobies use these find as ‘suction cups’, attaching themselves to smooth surfaces so that don’t have to swim all the time.

However, some fishes such as the gouramis have their pelvic fins in a rather anterior position, and they don’t even look like fins! Instead, they are so very elongate and are so modified that they serve the function of “feelers”! Check them out, checking each other out, the next time you’re in the aquarium store.

Do you know other functions fish have for these pelvic fins? Please do share them.