Raindow Trout fry syndrome

May | June 2014

Raindow Trout fry syndrome

The International magazine for the aquaculture feed industry

International Aquafeed is published six times a year by Perendale Publishers Ltd of the United Kingdom.All data is published in good faith, based on information received, and while every care is taken to prevent inaccuracies, the publishers accept no liability for any errors or omissions or for the consequences of action taken on the basis of information published. ©Copyright 2014 Perendale Publishers Ltd. All rights reserved. No part of this publication may be reproduced in any form or by any means without prior permission of the copyright owner. Printed by Perendale Publishers Ltd. ISSN: 1464-0058

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Salmonid aquaculture has suffered from a number of different ailments. Infectious Salmon Anaemia, caused by the Isavirus from the ortho-

mixoviridae family, led to a major crisis of the Atlantic salmon aquaculture industry in Chile, dramatically reducing production numbers.

Ectoparasitic conditions such as sea lice infestations and amoebic gill disease are affect-ing the salmon aquaculture industry through-out the world, causing major economic losses.

Bacterial infections are also common, caus-ing diseases such as Furunculosis or Bacterial Kidney Disease.

One of the bacteria that causes problems in salmonids is Flavobacterium psychrophilum. The first time it was isolated, it was from the kidney and external lesions of diseased coho salmon in Washington, USA [3].

At that time, the disease was given the name “peduncle disease” [12]. Infections with F. psychrophilium have since been labeled with many different names [3, 39, 26, 49, 7, 28, 25] but currently the names Bacterial Cold Water Disease (BCWD) [17, 22] and Rainbow Trout Fry Syndrome (RTFS) [40, 14] are commonly used in the USA and Europe respectively [1].

Until the 1980s the disease was only found in North American salmonids at low water temperatures (6°-10°C) [15]. Now it is found throughout the world.

RTFS has been identified in North America [17, 16], nearly every country in Europe [2, 43, 49, 53, 27, 38], Australia [44], Chile [52], Peru [25], Japan [52, 19] and Korea [23]. It can now

infest non-salmonid hosts, like common and crucian carp [24], European and Japanese eel [24, 20], ayu [52, 23], pale chub [19], roach [29] and tench [24].

The bacterium probably affects all types of salmonids [36] but the most susceptible species are rainbow trout and coho salmon [11, 22, 8].

The most severe outbreak of disease occurs in sac fry, where mortalities can reach up to 50 percent. In fingerlings, mortalities can range between 5-20 percent [15].

Furthermore, it has recently been noted that it is capable of causing disease at much higher water temperatures [15].

The bacteriaFlavobacterium psychrophilum are Gram-

negative bacteria cells that are flexible, weakly refractile, slender rods with rounded ends [17, 41, 30, 36]. The disease starts with the pres-ence of the pathogen in the water. Infected

fish shed bacterial cells into the water and dead infected fish shed cells at much higher numbers [31, 29]. The bacteria can also sur-vive for several months in fresh water outside the host [54, 51, 32, 35, 50]. Such infections, from one fish to another or from environmen-tal sources, are called “horizontal” pathogen transmissions. Vertical transmissions are from the parents to the offspring. This type of trans-mission is also probable with RTFS [5, 47]. The bacteria have been found on the exterior of the egg, the ovarian fluid and in milt [5, 47, 33]. Taking all this into consideration, it is assumed that the bacteria can enter the host via a combination of routes [36] and its adhesive properties can help in the successful colonisation of its tissues [36].

There are many environmental strains of F. psychrophilum and not all of them are pathogenic. There are at least three main serotypes [27, 21, 48] and several distinct genetic lineages with considerable genetic

RAINBOWTROUT fry syndrome

Table 1: Haemocytic activity of white leg shrimp

Parameter ControlEnro

10ppmOS

500ppmOS

1000ppmOS

2000ppmPool SE

Month 1 Phagocytosis (%) 13.12 10.29 10.02 13.32 15.74 1.821

Phagocytic Index 2.05 0.77 0.72 1.96 2.43 0.7281

Prophenol Oxidase Activity 0.17 0.21 0.5 0.59 0.58 0.0689







Aquaculture in its brief, modern

history has been hit by a number

of different diseases. Bacteria,

viruses and parasites can cause

serious problems for a fish farmer

by Kat Konstanti, International Technical Support Specialist, Meriden Animal Health

14 | INTERNATIONAL AQUAFEED | May-June 2014

FEATURE

and virulence variation [9, 29, 20, 45, 46, 37, 16, 38, 1]. This fact turns this disease into a bacteriology minefield.

TreatmentThe main method of treatment is use of

antibiotics. Oxytetracycline has often been used around the world against RTFS [39, 4, 22, 28]. Amoxycillin and oxolinic acid have widely been used In Europe [4, 6]. However the development of antibiotic resistance makes antibiotics an unsustainable method of treatment [15].

A lot of effort has been put into develop-ing a vaccine but little progress has been made so far [15, 1]. Some experiments with injectable vaccines, that have used either formalin-killed or heat-inactivated bacteria, have shown some promise but such vaccines

will be very impractical for farm scale fry inoculations [15, 1]. Until a viable vaccine is produced, the industry will have to rely on the use of antibiotics for treatment, along with good biosecurity and husbandry measures to possibly avoid the outbreaks.

Barnes & Brown (2011) [1] suggested that dietary research is warranted, such as an evaluation of novel dietary ingredients in feeds or improved feed formulations that lead to changes in RTFS susceptibility.

Orego-Stim Aquatract LOrego-Stim® is a natural feed additive

based on oregano, developed by Meriden Animal Health. The oregano essential oil acts as an immunity enhancer and growth promot-er, with further benefits including antibacterial and antimicrobial properties.

This section will be divided into two sub-sections. The first outlines the mode of action of oregano essential oil and the second dem-onstrates its immunity-boosting properties in aquaculture species. All the data in these sections is obtained from studies conducted by Meriden Animal Health.

Note: As the scope of this paper focuses on the antimicrobial and antibacterial effects of Orego-Stim®, growth promoting results are not shown in the main text, however results from commercial trials studying the growth promoting effects of the product on Rainbow trout, are shown in appendix 1 for reference.

Mode of ActionIndirectly, Orego-Stim® acts as a growth

promoter and an appetizer. It improves feed intake and digestion, boosts immunity and has antioxidant and anticoccidial properties. Primarily however, it is an antibacterial.

In general, gram-negative bacteria, in contrast to gram-positive bacteria, have both a cytoplasmic membrane and an outer lipid cell membrane with a much smaller peptidoglycan in between. As the ancestral types of bacteria do not have the outer-layer, it has been suggested that this extra outer-layer in the gram-negative bacteria has evolved as a protection against antibiot-ics. This is a theory that could explain why

Table 2: Phagocytosis Activity of Catfish under normal conditions

Month Parameter ControlEnro

10ppmOS

500ppmOS

1000ppmOS

2000ppmPool SE

Month 1Phagocytosis (%) 42.55 54.55 23.72 56.85 70.31 5.59

Phagocytosis index (%) 20.31 44.62 33.57 45.61 87.12 14.02

Month 2Phagocytosis (%) 9.54 10.57 14.23 14.22 17.00 4.84


Month3Phagocytosis (%) 32.73 33.34 29.77 33.85 40.42 5.53


May-June 2014 | INTERNATIONAL AQUAFEED | 15

FEATURE

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gram-negative bacteria are more resistant to antibiotic treatment.

Unlike antibiotics, OS has a very primitive mode of action. Orego-Stim contains unique levels of Carvacrol and Thymol which are natural phenols that act like disinfectants. The active ingredients of Orego-Stim® can alter the bacteria’s cell membrane, increasing its permeability and resulting in water imbalance and cell death. This inhibitory effect is not due to the transfer of any chromosomes, neither do they affect the cytoplasmic components of the cells, thus there is no risk of increasing bacterial resistance, like in the case of penicillin or streptomycin (Hui, n.d).

Immunity boostingTwo studies conducted at the Kasetsart

University in Thailand, focused on determin-ing the effectiveness of Orego-Stim® as an antimicrobial agent against pathogenic bacteria. The first study was conducted on white leg shrimp, Litopenaeus Vannamei. Five treatment groups were reared for three months. During that time, three groups were fed Orego-Stim® at different concentra-tions (500ppm, 1000ppm & 2000ppm), one group was treated with the commonly used in-feed antibiotic, enrofloxacin (10ppm) and a control group fed with the normal diet. The phagocytic index and the prophenol oxidase activity were measured monthly. Phagocytes are cells that protect the animal by ingesting foreign organisms such as bacte-ria. Prophenol oxidase activity measures the volume of enzymes produced which aid the

phagocytes in clearing pathogens from an organism. Table 1 shows the results of the study. It can be seen that the Orego-Stim® treated groups show better immune func-tion.

Following the three months, the shrimp where challenged with the virulent gram-neg-ative bacteria Vibrio harveyi. The challenge lasted for 10 days. The bacteria were intro-duced in two ways, by bath treatment and by oral administra-tion. In both cases, the vibrio bacteria count on the intestine and the hepatopancreas in the Orego-Stim® 2000ppm group was equal or lower than the control or the enrofloxacin treated groups. Furthermore, the Orego-Stim® 2000ppm group exhib-ited a significantly high-er survival rate.

A study with the same outline was con-ducted on hybrid catfish to evaluate the immune status of the fish, studied

under two conditions; normal temperature (27-32°C) and low temperature stress (22-24°C). The results are shown in tables 2 and 3.

Appendix 1: Growth Promotion Study on Rainbow Trout A commercial trial conducted by a Denmark fish feed producer studied the growth-promoting effects of Orego-Stim in rainbow trout. Table 1 shows the results after the 49-day study.

It can be seen that the inclusion of Orego-Stim in the feed increases the number of production while decreasing the FCR. On this study, it was further calculated that (including the cost of feed and Orego-Stim) the OS group added value of more than €3000

Table: Commercial Trial Data on the growth promoting effects of Orego-Stim on Rainbow Trout

ControlOrego-Stim

500ppmDifference

Average Start Weigh (g) 64.6 67.6

Average Final Weight (g) 107.3 114.3

Weight Gain (g) 42.7 46.7 +9.4%

Starting Biomass (Kg) 1,250 1,250

Final Biomass (Kg) 2,087.5 2,212.5

Biomass Gain (Kg) 837.5 962.5 +14.9%

Production of Fish (Kg) 51,450 57,330 +11.42%

Feed Used for Production (Kg) 47,849 51,597 +7.8%

Feed Conversion Ratio (FCR) 0.93 0.90 -3.2%

16 | INTERNATIONAL AQUAFEED | May-June 2014

FEATURE

It can be seen that in both the normal and stress conditions, the fish exhibit greater efficiency to enhance phagocytosis activity and percentage of phagocytosis, especially during the first month.

Subsequently they were challenged with the pathogenic bacteria Aeromonas hydroph-ila. During the bath treatment challenge, the groups treated with Orego-Stim® were as effective as the group being treated with antibiotics in preventing mortalities (100% survival rate). However the Orego-Stim® 1000-2000 groups were significantly more effective in eliminating A. hydrophilia in the intestines, without compromising beneficial lactic acid bacteria.

ConclusionRainbow trout fry syndrome has been

plaguing the salmonid aquaculture industry and has been causing severe economic losses through mortalities and cost of treatments which are becoming less effective as resistance develops. Currently this disease is in the top 5 diseases that cause economic problems in the UK aquaculture sector, possibly higher in the EU and USA sectors.

The use of antibiotics is becoming less and less sustainable. Certain antibiotics have been banned in animal use in many countries as they have been proved to be harmful for human consumption. The antibiotics that are available are becoming less effective from overuse or misuse. Furthermore, even when the antibiotics do work, their use requires what is called a “withdrawal period” to allow for any chemical residues that can be attained in the flesh to dissipate. During

this time, the fish are vulnerable to further infections.

As disease outbreaks will probably occur during a farming cycle, alternative preventative or therapeutic treatment options have to be put in place to help the farmers protect their livestock. With public opinion rapidly shifting against the use of chemicals and medications in their food, use of natural products that can fulfil that job would be the best option for both worlds.

With Orego-Stim® being this effective in combating bacteria directly and boosting the immunity of the organism, alongside its

growth promoting effects, further research on its ability to prevent outbreaks of RTFS is war-ranted. The easy in-feed application method for the farmers, along with the increased food consumption, the improved gut health and the antibacterial properties that pathogenic bacteria cannot defend against, all this turns Orego-Stim® to the 100% natural additive everyone has been waiting for.

References

Available at www.aquafeed.co.uk/ref4872

Table 3: Phagocytosis Activity of Catfish under Temperature Stress Conditions

Parameter ControlEnro

10ppmOS

500ppmOS

1000ppmOS

2000ppmPool SE





Month3 Phagocytosis (%) 28.98 31.53 31.77 33.26 34.62 3.23


More InforMatIon:Kat [email protected]

May-June 2014 | INTERNATIONAL AQUAFEED | 17

FEATURE

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