The Fish Vet's Blog

I get asked this question a lot especially relating to what’s the best practice for killing fish. It can depend in the situation. Is it a pet fish? Is it one caught when recreational fishing? Is it one from a live holding tank as often seen in restaurants? All these have one thing in common and it’s to do with paying individual attention to each fish.

The article below is just the work needed to provide evidence for best practice.

For the moment at least, it is not yet practical to roll it out to commercial wild catch fisheries. The aquaculture industry would do well to adopt such practices.

—
Now on: Twitter – Blog – Facebook – Linkedin

Aquaculture Volume 325, Number 9 (January 2012) Conditions for instant electrical stunning of farmed Atlantic cod after de-watering, maintenance of unconsciousness, effects of stress, and fillet quality — A comparison with AQUI-S™ Authors: U. Erikson, B. Lambooij, H. Digre, H.G.M. Reimert, M. Bondø, H. van der Vis Author Affiliations:

Source: Aquaculture, Volume 325, Number 9 (January 2012) Page Numbers: 135 – 144 Available Full Text:

Abstract: Electrical stunning of farmed Atlantic cod is a method used to render the fish unconscious before further processing. However, evaluations of the stunning method at plants have shown that the electrical parameters need to be optimized to achieve instant stunning and prolonged duration of unconsciousness. One aim of the present study was to establish suitable stunning conditions for cod to comply with future fish welfare regulations. AQUI-S™ is an anaesthetic capable of producing rested fish at slaughter. In the current study, we wanted to assess some welfare aspects of using this agent. In addition, the two stunning methods were compared in terms of the magnitude of the stress response, and the resulting effect on product quality. The data show it was possible to stun cod instantly (0.5s) at 107 Vrms, 0.5+0.2 Arms. However, it was necessary to expose the fish for a longer period (e.g. 15s) to the same voltage to prolong the period of unconsciousness to facilitate killing without recovery. AQUI-S™ (68mgL-1) rendered the fish unconscious without recovery. No noticeable avoidance behaviour or distress was observed during stunning. Blood pH, lactate levels, and blood drainage, as determined after recovery, were similar for both stunning methods. The ability of the white muscle to twitch was not affected by treatment although electrical stunning caused a drop in initial white muscle pH. Hence, a tendency for a more rapid onset of rigor mortis was observed. No detrimental effects on product quality (Quality Index scores, tendency for gaping, ultimate pH, and fillet texture) were observed for either stunning method. Moreover, no blood spots and discolourations of fillets, or spinal fractures were observed. To comply with both good fish welfare protocols, and at the same time ensuring good product quality, we have fundamentally shown that this is indeed possible when cod are stunned with either of the methods described here. Citation: U. Erikson, B. Lambooij, H. Digre, H.G.M. Reimert, M. Bondø, H. van der Vis . Conditions for instant electrical stunning of farmed Atlantic cod after de-watering, maintenance of unconsciousness, effects of stress, and fillet quality — A comparison with AQUI-S™. Aquaculture, Volume 325, Number 9 (January 2012), pp. 135-144, URL: http://ejournals.ebsco.com/direct.asp?ArticleID=43ED8BDFB6A8334FA1FE

Generally speaking, tropical fishes would do well in water temperatures kept between 24-26 degrees celsius. But for other species, it’s not a simple answer. There are several ways of determining this using scientific methods. Some studies use behavioural observations – scientists create a temperature gradient in long tanks to see where the fish spends more time in. In the article below, it uses a different measure to quantify the optimal temperature range – the metabolic rate.

—

Now on: Twitter – Blog – Facebook – Linkedin

Aquaculture Volume 325, Number 9 (January 2012) Thermal optimum for pikeperch (Sander lucioperca) and the use of ventilation frequency as a predictor of metabolic rate Authors: Michael Frisk, Peter Vilhelm Skov, John Fleng Steffensen Author Affiliations:

Source: Aquaculture, Volume 325, Number 9 (January 2012) Page Numbers: 151 – 157 Available Full Text:

Abstract: Pikeperch is of increasing interest to the aquaculture industry, as a novel high value species. To our knowledge there is currently no information available on the metabolic rates of adult pikeperch. The present study determined the standard and maximum metabolic rates and ventilation frequency at six temperatures, ranging from 13 to 28°C, in order to identify the temperature where pikeperch has the largest metabolic scope (MS). Between 13 and 25°C, standard metabolic rates (SMR) increased as expected with a Q10=1.8 in response to increasing temperatures, while maximum metabolic rate (MMR) did not change significantly within this temperature range. As a result, MS was not significantly affected by acclimation temperature between 13 and 25°C. Above 25°C, SMR increased significantly with a Q10=2.5 while MMR declined, resulting in a decreased MS. In the present study, the maximum MS (MSMAX) was found at 18.8°C. Defining the optimal temperature as the thermal range where fish can maintain 80% of MSMAX, shows that adult pikeperch have a broad thermal optimum between 10.4 and 26.9°C. Since earlier studies on juvenile pikeperch have reported an optimal temperature range of 25–30°C, we show that pikeperch have an ontogenetic shift in their thermal optimum, emphasizing the importance of considering fish size when deciding the temperature in aquaculture facilities. Citation: Michael Frisk, Peter Vilhelm Skov, John Fleng Steffensen . Thermal optimum for pikeperch (Sander lucioperca) and the use of ventilation frequency as a predictor of metabolic rate. Aquaculture, Volume 325, Number 9 (January 2012), pp. 151-157, URL: http://ejournals.ebsco.com/direct.asp?ArticleID=42A78EAA7F72194E6445

Did you know that a lot of our water pipes are made of copper? Do you know the effects of copper on aquatic organisms? The answer is easily “Googleable”.

However, what I’d like to share with you is that if the incoming water’s pH is acidic or the water is warm, then there could be higher than normal amounts of dissolved copper in the water you’ll be adding to your aquatic set-ups! In fact, it may be high enough to unintentionally create problems with your aquatic critters!

This is why you should never use hot/warm water from the tap for your aquaria. Also, it’s a good idea to check your tap water’s pH when you’re conducting large water changes.

—
Now on: Twitter – Blog – Facebook – Linkedin

Aquaculture
Volume 323, Number 1 (December 2011)
	Copper bioavailability and impact on bacterial growth in flow-through rainbow trout aquaculture systems
	Authors:	Andreas Tom-Petersen, Kristian K. Brandt, Ole Nybroe, Niels O.G. Jørgensen
	Author Affiliations:	no affiliations available
	Source:	Aquaculture, Volume 323, Number 1 (December 2011)
	Page Numbers:	259 – 262
	Available Full Text:	Full Text: Subscription Required to view full text Format: PDF Size: Unknown Location: Publisher’s Site Authentication: Publisher’s Site
	Abstract:	Copper is an important additive in the aquaculture industry for control of algal growth and ecto-parasites. However, copper may impact microbial communities depending on its biological availability and hence negatively affect microbial degradation of organic matter or other microbial ecosystem services. Here we applied a whole-cell bacterial biosensor to determine copper bioavailability (proportion of bioavailable vs. total copper) in water from three rainbow trout aquaculture facilities. Copper bioavailability varied between 24 and 37% and the differences were compatible with differences in carbonate alkalinity, concentration of dissolved organic matter and amounts of suspended matter in the water. Subsequently, we determined the effect of copper on bacterial growth activity at concentrations realistic for aquacultures. Although a field exposure to ca. 0.1µM bioavailable Cu had no effect, laboratory exposure to comparable concentrations reduced the bacterial growth activity. Hence, common copper amendment procedures may lead to concentrations close to the threshold that impacts bacterial activity.
	Citation:	Andreas Tom-Petersen, Kristian K. Brandt, Ole Nybroe, Niels O.G. Jørgensen . Copper bioavailability and impact on bacterial growth in flow-through rainbow trout aquaculture systems. Aquaculture, Volume 323, Number 1 (December 2011), pp. 259-262,
	URL:	http://ejournals.ebsco.com/direct.asp?ArticleID=484CA2BB418460FAC7CC

I Frequently get interviewed by various organisations about fish welfare. Currently, I provide feedback to queries raised by the RSPCA and also, by the animal ethics committees of universities and schools. I try to provide the most up to date information, however, there remains more work to be done.

What we need to understand is that ‘fish’ are a diverse range of animals. one fish species is not necessarily the same as another and so we cannot generalise in some cases.

Let me illustrate an example using ‘birds’ as a group. When you compare what the requirements for ducks – need water to paddle and dive, ability to fly, balanced diet including greens and aquatic invertebrates… This cannot be applied to an ostrich! An ostrich would drown!

work such as the one in this article attached would be needed in a wide range of fish. And we need to be objective about things.

Aquaculture
Volume 323, Number 1 (December 2011)
	Short- and long-term effects of fish density and specific water flow on the welfare of Atlantic cod, Gadus morhua
	Authors:	Børge Damsgård, Frode Bjørklund, Helge K. Johnsen, Hilde Toften
	Author Affiliations:	no affiliations available
	Source:	Aquaculture, Volume 323, Number 1 (December 2011)
	Page Numbers:	184 – 190
	Available Full Text:	Full Text: Subscription Required to view full text Format: PDF Size: Unknown Location: Publisher’s Site Authentication: Publisher’s Site
	Abstract:	Intensive rearing of farmed fish may have potential welfare related consequences on a short-term and long-term scale. Groups of individually tagged juvenile Atlantic cod, Gadus morhua, were held in eight tanks for 9weeks at different rearing intensities, given as combinations of fish density and specific water flow (litrewaterperkg-1fishpermin-1). The control groups (LD-HF) had low density (~30kgm-3) and high specific water flow (0.84lkg-1min-1), while the other groups had high density (~60kgm-3) and either high specific water flow (HD-HF, 0.84lkg-1min-1), or low specific water flow (HD-LF, 0.17lkg-1min-1). Oxygen was added to maintain an O2level of 80% saturation in all tanks. The groups were pooled after the nine week treatment period, transferred to a sea cage and reared under standard conditions for 14.5months, until reaching an average body size of approximately 1.4kg. A combination of high fish density and low water flow (HD-LF) resulted in accumulation of CO2in the water. This, in turn was associated with significantly higher blood pCO2, a higher frequency of nephrocalcinosis, and a 20–30% reduction in growth, as compared with the other groups. The sub-optimal growth observed in the HD-LF groups was not fully compensated for after transfer to the sea cage, with the fish of the LD-HF and HD-HF groups being 5–10% larger than the HD-LF fish by the end of the experiment.
	Citation:	Børge Damsgård, Frode Bjørklund, Helge K. Johnsen, Hilde Toften . Short- and long-term effects of fish density and specific water flow on the welfare of Atlantic cod, Gadus morhua. Aquaculture, Volume 323, Number 1 (December 2011), pp. 184-190,
	URL:	http://ejournals.ebsco.com/direct.asp?ArticleID=4E76982CA2056EA97165

It’s commonly said in the aquaculture circles that if you start with cr@p, you end with cr@p. This is especially true when choosing your seed stock / fingerlings. You need to get good quality stock to get good grow out and good feed conversion, otherwise you’ll be losing valuable time and money.

In the shrimp sector, the larvae are put through challenge trials (they are exposed different salinity or exposed to formalin). If a certain threshold percentage survives, then they will be bought by the farmer.

This article details another means of objective measurement of seed stock quality by evaluating their morphometric ratios as it applies to seahorses – trunk width : trunk length.

Aquaculture
Volume 323, Number 1 (December 2011)
	Criteria for assessing juvenile quality of the lined seahorse, Hippocampus erectus
	Authors:	Dong Zhang, Fei Yin, Junda Lin
	Author Affiliations:	no affiliations available
	Source:	Aquaculture, Volume 323, Number 1 (December 2011)
	Page Numbers:	255 – 258
	Available Full Text:	Full Text: Subscription Required to view full text Format: PDF Size: Unknown Location: Publisher’s Site Authentication: Publisher’s Site
	Abstract:	Juvenile quality has been demonstrated to be the key for commercial fish production. Variations in juvenile quality leading to varying growth and mortality are often encountered and well documented in many marine fish species. It is valuable to discover simple and reliable indicators for assessing juvenile quality in fish aquaculture. In this study, we established criteria for evaluating the juvenile quality of the lined seahorse, Hippocampus erectus, a Chinese traditional medicine and popular aquarium species. We raised 18 batches for 45days from birth to determine the potential criteria for assessing the juvenile quality of the line seahorse. There was a strong and significant correlation between survival through the fifth day and that on the day 45. By comparing the ratio of trunk width at 1/2 trunk length to trunk length (TW/TL) of dead and live juveniles during the first 5days, we found that TW/TL is a reliable indicator of the juvenile quality, with the distinct threshold of 0.190.
	Citation:	Dong Zhang, Fei Yin, Junda Lin . Criteria for assessing juvenile quality of the lined seahorse, Hippocampus erectus. Aquaculture, Volume 323, Number 1 (December 2011), pp. 255-258,
	URL:	http://ejournals.ebsco.com/direct.asp?ArticleID=4DC59AE1453B881A037A