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Viral diseases of aquarium fish

April 1995
Seminars in Avian and Exotic Pet Medicine 4(2):103-110

Authors:

The Commonwealth Scientific and Industrial Research Organisation

Ornamental fish are susceptible to many viral pathogens, some of which are readily identifiable, whereas others remain obscure. Identification is not always possible owing to lack of resources or inability of the virus to grow in available fish cell lines. In many instances viral infection may remain latent until adverse environmental conditions, such as poor water quality, overcrowding, or rough handling, trigger the onset of disease. Frequently the only course is to destroy the fish and effectively disinfect all equipment. Consequently, for many viral pathogens, our knowledge of the etiology of the associated disease remains minimal. In this article we review not only those diseases of ornamental fish with a well-established viral etiology but also those conditions that may be associated with, but not necessarily caused by, a viral infection. Moreover, also included are other reports of single cases that are also important because they represent exotic incursions.

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Viral Diseases of Aquarium Fish

Eva-Maria Bernoth, DVM, and Mark StJ Crane, PhD

Ornamental fish are susceptible to many viral patho-

gens, some of which are readily identifiable, whereas

others remain obscure. Identification is not always pos-

sible owing to lack of resources or inability of the virus

to grow in available fish cell lines. In many instances

viral infection may remain latent until adverse environ-

mental conditions, such as poor water quality, over-

crowding, or rough handling, trigger the onset of dis-

ease. Frequently the only course is to destroy the fish

and effectively disinfect all equipment. Consequently,

for many viral pathogens, our knowledge of the etiol-

ogy of the associated disease remains minimal. In this

article we review not only those diseases of ornamental

fish with a well-established viral etiology but also those

conditions that may be associated with, but not neces-

sarily caused by, a viral infection. Moreover, also in-

cluded are other reports of single cases that are also

important because they represent exotic incursions.

Key words: Aquaria, ornamental fish, viruses, disease.

lthough, in recent years, there has been a

worldwide increase in both basic and ap-

plied research concerning viral diseases and vi-

ral infections of fish species important to the

aquaculture industry, the number of published

papers on viruses of aquarium fish remains

relatively low. a'2 The major reason for this in-

equity is the higher socioeconomic importance

placed on fish destined for human consump-

tion. Consequently, the vast majority of re-

search funds available for fish diseases is chan-

nelled into projects targeted at food-fish dis-

eases rather than diseases of ornamental fish.

This is especially true for viral disease research

that requires the use of sophisticated and costly

equipment such as light and electron micro-

scopes. Furthermore, there is little incentive

for private aquarium fish owners to authorize

detailed and expensive virological examina-

tions, where a positive diagnosis, in most cases,

From the AAHL Fish Diseases Laboratory, CSIRO Australian

Animal Health Laboratory, Victoria, Australia.

Address reprint requests to Eva-Maria Bernoth, DVM,

AAHL Fish Diseases Laboratory, CSIRO Australian Animal

Health Laboratory, Private Bag 24, Geelong, Victoria 3220.

1055-937X/95/0402-000755.00/0

results in destruction of the fish rather than

implementation of a treatment with the possi-

bility of a cure.

Most published information on viral dis-

eases of aquarium fish is in case reports or

sometimes in reports of incidental findings of

viruses in otherwise healthy fish. 3-9 Difficulties

in culturing viruses from ornamental fish of-

ten make transmission studies impossible,

Henle-Koch's postulates cannot be fulfilled,

and the etiological role of viruses associated

with disease conditions remains questionable. 9-17

Subclinical Viral Infections

Aquarium fish often live in suboptimal con-

ditions involving limited volumes of water in

aquarium systems with a restricted capacity to

maintain adequate water quality; unlike feral

fish, they cannot escape a potentially harmful

environment. Even the best-equipped aquar-

ium, combined with rigorous surveillance of

water quality parameters, can never truly

mimic natural conditions in the wild. Thus, the

keeping of fish in aquaria is a compromise that

usually has a negative influence on the fish's

well-being.

In this respect, Snieszko

developed the

frequently quoted graphic of three overlap-

ping circles representing the host (ie, the fish),

the pathogens, and the environment, to show

the single and combined influences of infec-

tious agents and noninfectious parameters on

fish health (Fig 1). This simple graphic illus-

trates the influence of not only the physical

environment as well as the presence of poten-

tial pathogens but also their interaction on fish

health. Aquarium fish may harbor viruses

without any clinical signs yet become diseased

with the slightest decrease in water quality. Pa-

rameters that have significant influence on wa-

ter quality include dissolved oxygen, sus-

pended solids, organic content, and nitrogen

concentration in the form of ammonia and ni-

trite. Unless these parameters remain within

Seminars in Avian and Exotic Pet Medicine, Vol 4, No 2 (April), 1995: pp 103-110

103

104

Bernoth and StJ Crane

disease

environment

Figure 1. Effect of internal and external influences

on fish health. The three circles represent the fish

(host), any pathogens or parasites, and the aquatic

environment. An inadequate environment (eg, low

water quality) compromises the fishes' health (over-

lapping of two circles); the risk of a disease outbreak

increases as soon as any pathogen or parasite enters

the environment (overlapping of three circles).

(Adapted with permission? ~)

their optimum range, they will contribute to

the overall stress experienced by the inhabitant

fish. Indeed, a stress-related outbreak of a la-

tent herpesvirus infection in angelfish

(Ptero-

phyllum altum)

has been reported by Meller-

gaard and Bloch. 12 Moreover, stress factors

other than changes in water quality include not

only poor food composition or feeding prac-

tices but also changes in an established popu-

lation of aquarium fish owing to stocking with

new specimens, overcrowding, or rough han-

dling practices.

Thus, development of a viral infection to

the onset of disease is a multifactorial process,

and there are no treatments available for spe-

cific viral infections. Early d{agnosis is critical

so that the clinician can attempt to reduce mor-

tality associated with disease by correcting any

contributory factors such as overcrowding,

poor water quality, and secondary bacterial in-

vaders

(Aeromonas

species,

Flexibacter

species,

Pseudomonas

species), a9

Subclinical viral infections in aquarium fish

not only render the fish susceptible to that par-

ticular virus, but the constant presence of an

infectious organism can also exhaust the fish's

immune system, making it more vulnerable to

other infectious agents or noninfectious prob-

lems. 6 There is also another risk involved with

subclinical viral infections. Infected fish may

have an effective immune system and not show

clinical signs of disease but may become carri-

ers of the virus. Consequently, other more sus-

ceptible fish of the same or different species

cohabiting in the aquarium system may be-

come infected. 2~ Although such a transfer may

be harmful for an established aquarium pop-

ulation, a disease outbreak could be contained

within the aquarium system. However, once

such subclinically infected fish are released

into open waterways (either inadvertently or

intentionally), the possible risk to wild fish

populations becomes unpredictable. The etio-

logical agent of a severe disease of Common

Carp

(Cyprinus carpio),

Spring Viraemia of

Carp virus (SVCV), is believed to have been

introduced into the United Kingdom with im-

ported goldfish

( Carassius auratus). 2~

When-

ever there is a new outbreak of SVCV in orna-

mental fish in the United Kingdom, strict bans

and restrictions apply to prevent spread of the

disease. 22'23 Similarly, in the United States,

carp pox caused by

Herpesvirus cyprini

had not

been seen before the importation of clinically

healthy Golden Ide

(Leuciscus idus). 24

Further-

more,

Herpesvirus cyprini,

first isolated from

diseased Ornamental (Asagi) Carp in Japan, 25

has been inoculated into an important food

fish, Common Carp, which subsequently de-

veloped papillomas. 26

Once ornamental fish are released, there is

little chance of their recapture, and the rate of

survival in the wild can be high. Cold-water

ornamental fish such as koi or shubunkin are

known to survive well in temperate climates. In

Australia's warm-water systems, even tropical

fish can build stable populations. McKay's list 27

of "exotic fishes successfully introduced into

Australian freshwater" comprises the mosqui-

to fishes

(Gambusia affinis affinis, G affinis hol-

brooki

and

G dominicensis),

guppy

(Poecilia retic-

ulata),

Sailfin Molly

(P latipina),

swordtail

(Xi-

phophorus helleri),

platy

(X maculatus),

tilapia

(Tilapia mossambica),

Spotted Tilapia

(T mariae),

Convict Cichlid

(Cichlasoma nigrofasciatum),

Jack Dempsey

(C octofasciatum),

and goldfish

(Carassius auratus).

Mosquitofishes, guppies,

Sailfin Mollies, and goldfish have also estab-

lished populations in New Zealand. 2s

It must be noted that transmission of disease

Viral Diseases of Aquarium Fish

105

agents among susceptible fish is not necessarily

restricted tO water-borne routes. Fish-eating

birds such as the Gray Heron

(Ardea cinerea)

have been shown to transmit viral pathogens

via their feces (infectious pancreatic necrosis

virus [IPNV]) or by reg6rgitation of food

(SVCV and viral hemorrhagic septicemia virus

[VHSV]) 21'29

and blood-sucking parasites such

as carp lice

(Argulusfoliaceus)

and the leech

(Pi-

scicola geometra)

can serve as mechanical vectors

for SVCV. ~~ It is possible that similar mech-

anisms, as yet undocumented, are involved in

the transmission of other viral pathogens.

The perceived risks associated with aquar-

ium fish carrying viral pathogens are most ev-

ident whenever exotic fish species are to be

imported. Fish may appear clinically healthy,

survive quarantine periods without appear-

ance of any suspicious signs of infection, and

yet may harbor a virus that poses a threat to

private collections and indigenous species of

fish. In Australia, freshwater ornamental fish

on a special Permitted Species List 32 can be

imported under provisions of the Common-

wealth of Australia legislation. During a quar-

antine period of 2 weeks, fish are observed for

clinical signs of disease, but this inspection

does not guarantee the absence of virus;

Anderson et a116 have reported incidental de-

tection of iridoviruslike particles in imported

dwarf gourami. The many examples of in-

troductions of exotic fish pathogens with im-

ports of exotic fish species, the consequences

thereof, and the means to prevent such intro-

ductions in future have become major interna-

tional issues requiring regulation. 2~ In

Australia, proposals have been considered to

extend the inspection for clinical disease dur-

ing quarantine to specific health accreditation

or to include random sampling of all imported

batches. 16 Currently, Australia's quarantine

policy on fish imports is under review, 37 and it

is possible that changes to the policy will be

recommended.

Specific Viral Diseases of

Aquarium Fish

Generally, diagnosis of viral infections can

only be presumptive in normal veterinary

practice. Sometimes (eg, lymphocystis disease),

the clinical picture may be almost sufficient to

verify the suspicion, but usually at least light

microscopic examination of tissue sections will

be required for verification. For definitive

identification, virus isolation in cell culture is

normally required but not always possible. For

details on the isolation and growth of viruses in

cell cultures, readers should consult more com-

prehensive publications which are listed in the

reference section. Moreover, it is worthwhile

noting that the response to any systemic viral

or bacterial infection often results in several

nonspecific clinical signs that include lethargy,

inappetence, darkening of the skin, exoph-

thalmia, dropsy, respiratory distress, uncoor-

dinated swimming movements, hemorrhages

in the skin (especially at the base of the fins and

around the vent), and pseudofeces (material

including mucus and intestinal epithelium

which, caused by the infection, has sloughed

off into the gut lumen and is often observed

trailing from the vent). Such signs by them-

selves cannot be used to identify the causative

agent of an ongoing infection.

There are no cures available for viral infec-

tions in fish, nor are there any vaccines avail-

able for their prevention. Rarely (eg, lympho-

cystis disease), surgical removal of affected ar-

eas may be an option, 9,~s such as when lesions

in the mouth region interfere with feeding.

However, currently the only effective means of

preventing viral disease is to restrict importa-

tion of exotic fish species, to comply with quar-

antine regulations and/or recommendations,

to implement disinfection, to observe other hy-

gienic practices in a strict manner, and to op-

timize the fishes' environment. Moreover, the

only possible means to treat viral disease is to

destroy the clinically infected fish, as well as

any other fish suspected of being infected, in a

way that prevents further spread of the agent,

either by incineration or burial and to destroy

or effectively disinfect any related equipment.

The following is a compilation of data ob-

tained from original papers and review articles

and includes the important viral diseases of

aquarium fish and also incidental virus find-

ings in otherwise healthy fish, single case re-

ports, and reports where the etiological signif-

icance of the virus remains questionable. In ad-

dition, recent detailed reviews can be found in

various chapters of the comprehensive text,

Fish Medicine,

edited by Stoskopf. 7-9'39'4~

106

Bernoth and St J Crane

Lymphocystis Disease

Lymphocystis disease, caused by iridovi-

ruses belonging to the genus

Lymphocystivirus,

a chronic disease that occurs worldwide 41'42

and is found in a broad range of warm- and

cold-water and freshwater and saltwater fish

species. The disease is typified by the occur-

rence of macroscopically visible pearllike or

wartlike nodules on the skin and fins and

sometimes in the mouth region, gills, or eye.

Although there are reports of diameters up to

15 mm, 4~ the nodules are normally 0.3 to 2.0

mm in diameter. Moreover, they can vary in

color and appear either white, cream, brown,

grey, or pink, depending on the overlying ep-

ithelium and state of vascularization. Normally

the nodules take 1 to 3 months or, sometimes,

up to a year to develop and are caused by in-

fection of connective tissue fibroblasts, usually

in the skin but sometimes on internal organs

such as the spleen. 44 These lymphocysts de-

velop as the grossly hypertrophic infected

cells 41'44'45 are encapsulated by proliferating

fibroblasts and the cysts are invaded by inflam-

matory cells (lymphocytes, plasma cells, mac-

rophages, and polymorphonuclear leucocytes).

This inflammatory response marks the begin-

ning of the healing process that can take up to

9 months. 4a The cysts eventually turn necrotic

and slough off leaving an intact epidermis. Al-

though the infection is seldom fatal, it is un-

sightly and can interfere with feeding when

the lesions are in the mouth region. It is prob-

able that infection occurs via skin abrasions,

gills, or by ingestion of infected cells, and dis-

semination of virus occurs when cysts slough

off

and/or rupture. The disease is diagnosed

by the appearance of the nodules but can

sometimes be confused with other infec-

tions 9'42 such as "white spot" caused by

Ich-

thyophthirius multifiliis.

It is of interest that a

similar condition has been reported by Mar-

tinez-Picado et a117 in the mudskipper

(Parap-

.ocryptes serperaster)

but with no evidence of cell

hypertrophy. Definitive diagnosis of lympho-

cystic disease is made by histological examina-

tion, isolation of the causative virus in cell cul-

ture when possible, and/or examination by

electron microscopy.

Viral Erythrocyte Necrosis (VEN)

As the name of the disease suggests, VEN is

an infection of erythrocytes resulting in ane-

mia indicated by pale appearance of the gills

and visceral organs and hyperactive hemato-

poietic tissue. The disease has been confirmed

in marine species such as wrasses and comb-

tooth blennies, but is present in many other

species, with young fish being more suscepti-

ble. Diagnosis is confirmed using stained blood

smears that show small eosinophilic inclusion

bodies in the red blood cell cytoplasm and vac-

uolated or degenerated nuclei. VEN has been

associated with an iridovirus 46 but, as yet, the

virus has not been isolated.

Other Infections of Aquarium Fish Related

to Iridoviridae

There is a single report of an acute disease

in imported Ramirez' Dwarf Cichlids

(Apisto-

gramma ramirezi)

from South America into the

United States, with 100% morbidity and 40%

to 80% mortality. 1~ The condition was asso-

ciated with widespread degenerative histopa-

thology in the internal organs, particularly the

spleen and eye. Externally, affected fish

showed the normal nonspecific clinical signs of

a systemic infection referred to in the intro-

duction but, although icosahedral particles

were detected by electron microscopy, no virus

was isolated nor identified.

Armstrong and Ferguson 1~ reported a sys-

temic viral disease in Chromide Cichlid

(Etroplus maculatus)

imported into the United

States from Singapore. The fish were very thin

and obviously anemic showing gill pallor and

progressive weakness leading to death. A virus,

presumptively belonging to the

Iridoviridae

and

different from Ramirez' Dwarf Cichlid Virus,

was detected but not isolated. Histological ex-

amination showed almost complete replace-

ment of hematopoietic renal interstitial tissue

by a heterogeneous population of hyper-

trophic cells and widespread occurrence of

cells at various stages of necrosis. Of further

interest is the isolation of two viruses from

healthy goldfish swimbladder cell cultures, 4

goldfish virus-1 and goldfish virus-2, with ul-

trastructural features of

Iridoviridae.

However,

there are no data from any histological or in-

fectivity studies.

Carp Pox, Epithelioma Papillosum

Carp pox, caused by

Herpesvirus cyprini,

is a

chronic disease occurring mainly in older

(greater than 1-year-old) fish. 4~ It is found in

Viral Diseases of Aquarium Fish

107

most species of carp and in a wide range of

other cyprinids and various aquarium fish spe-

cies in North America, Europe, Asia, and Is-

rael. 24-26'47 Presumptive diagnosis is based on

clinical signs (ie, macroscopically visible milky-

white/grey plaques), sometimes with a gelati-

nous appearance, which occur on the body sur-

face, including the fins, and are comparable

with drops of candlewax. Individual lesions

can be as large as 3 x 7 mmin Koi Carp as and

as they gradually increase in size, the lesions

may coalesce to cover large areas. Described as

"benign epidermal hyperplasia, ''4~ the lesions

are restricted to the epidermis and can be eas-

ily removed. 49 Although the lesions are un-

sightly and can develop into tumors after sev-

eral weeks or months, mortalities have not

been reported. Typical of herpesvirus infec-

tions, immunity is not very strong with no sig-

nificant inflammatory response, 4~ and infec-

tions can often be latent with lesions develop-

ing during periods of stress. Diagnosis can be

confirmed by virus isolation in cell cultures.

Other Infections of Aquarium Fish Related

to Herpesviridae

Another herpesvirus infection has been re-

ported in three adult angelfish

(P altum) a2

from Denmark. Although herpesvirus parti-

cles were detected in the nuclei and cytoplasm

of splenic macrophages/monocytes, no virus

has been isolated. The disease appeared to be

stress related with no specific signs, but the fish

displayed many of the nonspecific signs of a

systemic infection such as loss of equilibrium,

spiral swimming movements, and skin hemor-

rhages.

Diseases of Aquarium Fish Caused

by Birnaviridae

Infectious Pancreatic Necrosis (IPN),

caused by IPN virus (IPNV - Family

Birnaviri-

dae),

is a disease usually identified with cul-

tured salmonids. However, included in

Birna-

viridae

are other IPN-like viruses that infect

both salmonid and nonsalmonid fish species

including ornamental fish. Birnaviruses have a

worldwide distribution in a range of salmonid

and nonsalmonid freshwater and saltwater fish

and also some shellfish species; ~the precise

geographical and host distribution is not fully

known, but clearly birnaviruses are extremely

widespread. To date, birnaviruses have not

been isolated in Australia, but there is a re-

port 5~ describing the isolation of a birnavirus

from Quinnat Salmon

(Oncorhynchus tshaw-

ytscha)

returning to New Zealand from the sea.

Owing to the broad range of host species and

the many opportunities for entry into Austra-

lia, IPNV is a major concern to the Australian

salmonid aquaculture industry. Among orna-

mental fish, IPNV has been isolated from gold-

fish

(C auratus)

and discus fish

(Symphysodon dis-

cus)) In addition, an IPN-like virus has been

isolated from marine tropical reef fish. 9 For a

recent list of known hosts the reader should

consult the work of McAllister. 39

Classical IPN of salmonids is an acute,

highly contagious disease, mainly of fry, which

can cause up to 100% mortality. Survivors of

an epizootic outbreak have established an im-

munity but probably remain carriers of latent

infection with no clinical signs for the remain-

der of their lives. For information on the clin-

ical signs of classical IPN, the reader is re-

ferred to other reviews. ~9'5a In nonsalmonids,

infections can be acute with high mortalities 3'9

but with no specific clinical signs. Some non-

specific signs such as anorexia, disorientation,

swimming upside down, lethargy, and pete-

chial hemorrhages at the base of fins and

pseudofeces are common. Moreover, histo-

pathological lesions are rarely observed. Diag-

nosis is confirmed by virus isolation in a variety

of salmonid and/or nonsalmonid fish cell lines.

In salmonids, the mode of virus transmis-

sion by shedding via the feces, and excretory

and sexual products (ie, both horizontal and

vertical routes) with viral entry occurring via

the gills, or lateral line pores or by ingestion of

contaminated food is well established. In orna-

mental fish, vertical transmission has been con-

firmed experimentally in zebra fish

(Brachy-

danio rerio). 52

Spring Viraemia of Carp

Spring Viraemia of Carp, caused by the

rhabdovirus

Rhabdovirus carpiae

(RVC), is

quoted as "undoubtedly the most important vi-

rus disease of ornamental, as well as wild and

farmed carp. ''2~ It has a worldwide distribution

except for North America and Australia and

occurs mainly in young fish (less than 1 year

old) of all major cyprinid species. In addition,

guppies have been shown to be experimentally

susceptible.

108

Bernoth and StJ Crane

A variety of clinical signs have been de-

scribed,'most of which are nonspecific. These

include lethargy, darkening of the skin, respi-

ratory distress, exophthalmia, petechial hem-

orrhages of the skin andgills, pseudofeces, in-

flamed and protruding vent, and loss of bal-

ance (sometimes fish appear to stand on their

heads or their tails). Internal signs include

those typical of a viral septicemia with all or-

gans affected, ie inflammatory oedema, necro-

sis in all organs (liver, pancreas, kidney, heart,

brain, intestine, swimbladder), visceral hemor-

rhages and serosanguineous fluid in the ab-

dominal cavity. Inflammation of the swimblad-

der is the cause of loss of balance; in cases

where only one chamber of the swimbladder is

involved, head/tail standing is often exhibited,

depending on whether the posterior or ante-

rior chamber is affected. It should be noted

that the virus isolated from cases of swimblad-

der inflammation (SBIV) in carp is indistin-

guishable from

RVC. 20'40

As with other diseases of temperate fish spe-

cies, disease outbreaks often start with increas-

ing water temperatures, and survivors become

carriers of latent infection. During periods of

stress, virus is shed with mucus and feces; the

gills are considered the site of entry. The ad-

ditional problem of SVCV transmission by vec-

tors, mentioned previously9 '~a emphasizes

the need for good husbandry practices, espe-

cially in outdoor aquaria such as garden ponds.

Other Infections of Aquarium Fish Related

to Rhabdoviridae

There is a report 5~ of an acute disease with

subsequent isolation of a rhabdovirus in Rio

Grande Perch (cichlid), also known as the

North American (Mexican) Cichlid

(Cichlasoma

cyanoguttatum)--a

shipment of 50 specimens

showing signs of lethargy all died within 1

week. No further information is available from

the literature.

Striped Snakehead Skin Ulcerative disease,

causing large, deep ulcerations of the skin on

the head and body of Striped Snakehead

(Ophicephalus striatus)

in Burma and Thailand,

has been reported from two groups of au-

thors.

54-56

A rhabdovirus, serologically distinct

from other rhabdoviruses, such as VHSV of

salmonids, RVC, Pike Fry rhabdovirus, infec-

tious hematopoietic necrosis virus of salmo-

nids, eel rhabdoviruses, and perch rhabdovi-

rus was isolated, but its etiological significance

remains uncertain. Nevertheless, many species

of feral and pond-cultured freshwater and

brackish water fishes in Southeast Asia appear

susceptible, with outbreaks in Thailand occur-

ring in the cooler months.

Other Infections of Aquarium Fish Related

to Viruses

There are other reports 7-9'4~ of clinical dis-

ease signs in ornamental fish that could be re-

lated to viruses but where the etiological role of

the associated viruses remains obscure. Addi-

tionally, these reports are single case studies,

and the findings were not observed again. Re-

ports not covered in other reviews are the oc-

currence of retroviruslike particles in 20 angel-

fish

(PterophyUum scalare), 57

suffering from lip

fibromas but otherwise healthy, and the find-

ing of a reovirus associated with head and lat-

eral line erosion in a Marine Angelfish

(Poma-

canthus semicirculatus). 5s

References

1. Agius C: Virus diseases of warm water fish, in Roberts

RJ (ed): Microbial Diseases of Fish. London, Aca-

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2. Hill BJ: Virus diseases in temperate and tropical

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3. Adair BM, Ferguson HW: Isolation of infectious pan-

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4. Berry ES, Shea TB, Gabliks J: Two iridovirus isolates

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Carassius auratus

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Viral Diseases of Aquarium Fish

109

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155, 1988

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Looking for a bottleneck: Assessment of factors influencing post-stocking survival of advanced fingerling Walleye Sander vitreus

Thesis

Aug 2020

Emily E Grausgruber

Walleye Sander vitreus is a highly valued sportfish in North America. In 2001, 3.8 million anglers spent approximately 51.9 million days angling for Walleye (USFWS-USCB 2002). The popularity of Walleye has resulted in situations where demand exceeds supply, which has led to the development and implementation of stocking programs across the United States and Canada to enhance fishing opportunities (Lathrop et al. 2002), rebuild depleted stocks (Johnson et al. 1996; Li et al. 1996), and mitigate poor year classes from variable natural recruitment (Mitzner 1992; Johnson et al. 1996; Jennings et al. 2005; Logsdon et al. 2016; Reed and Staples 2017). However, mortality rates of stocked fishes can vary widely (27-95%; Stein et al. 1981; Buckmeier et al. 2005; Freedman et al. 2012; Weber et al. 2020) and small changes in survival can result in large differences in year-class strength and success of stocking initiatives. Numerous biotic and abiotic factors can influence survival during early life stages of fish, such as transportation and stocking practices (Forsberg et al. 2001; Barton et al. 2003), predation (Santucci and Wahl 1993; Buckmeier et al. 2005; Thompson et al. 2016), available forage (Johnson et al. 1996; Hoxmeier et al. 2006), competition (Le Pape and Bonhommeau 2015; Chase et al. 2016), fish origin (Kellison et al. 2000; Jonsson and Jonsson 2003; Pollock et al. 2007), body size (Litvak and Leggett 1992; Meekan et al. 2006; Grausgruber and Weber in press), and water temperatures (Akimova et al. 2016; Wagner et al. 2017). Furthermore, the aforementioned factors do not act independently of each other, making it challenging to determine their importance. The growth-predation hypothesis predicts that selective mortality should decline as individuals grow and increase in size (Anderson 1988). Increases in size are also associated with decreased predation risk (Post and Evans 1989; Miranda and Hubbard 1994), where larger body size can reduce the chances of predation due to improved maneuverability and swimming speed (Videler 1993). The argument of "bigger-is-better" (Butler 1988; Miller et al. 1988; Litvak and Leggett 1992) has led hatcheries to raise progressively larger fingerling Walleye (Halverson 2008). However, hatchery production is an expensive and labor-intensive process, where production costs are generally positively related to rearing duration and fish size (Wedemeyer 2001). Therefore, it is advantageous to evaluate factors hypothesized to limit post-stocking Walleye survival (e.g., effects of transport duration and handling practices as well as post-stocking predation and starvation) to assess whether rearing larger fingerling Walleye (hereafter referred to as Walleye) is justifiable. The objectives of this dissertation included 1) evaluating relationships between Walleye transport duration with changes in water chemistry parameters, Walleye physiology, and short-term (48 hr) mortality; 2) evaluating whether consumed Walleye total length was related to predator total length, predator gape height, or the probability of predation, as well as assessed whether length distributions varied among stocked, recaptured, and consumed Walleye, and estimate cumulative consumption for up to two months by a suite of piscivores; 3) evaluating diet composition and shifts of stocked Walleye; and 4) use mark-recapture techniques to evaluate the influence of predation, stocking environment, and Walleye physical characteristics on apparent weekly survival of Walleye from stocking until ice cover. For my first objective, I used two approaches (i.e., field and experimental evaluation) to evaluate relationships between Walleye transport duration with changes in water chemistry parameters, Walleye whole blood glucose and plasma cortisol concentrations, and short-term (48 hr) mortality. For the field evaluation, Walleye were transported between 3.5 to 6 hours and stocked into holding cages located at one of six systems. Water quality and Walleye stress (via whole blood glucose and plasma cortisol) and mortality were evaluated prior to, during, and at 0, 2, 24, and 48 hours post-transportation. During transport, water temperatures generally decreased while carbon dioxide concentrations fluctuated between 2.7 and 22.5 mg/L. Walleye whole blood glucose and plasma cortisol concentrations varied by system and time since transport. Changes in carbon dioxide concentrations were associated with changes in whole blood glucose concentrations. However, cumulative survival rates and plasma cortisol concentrations were not associated with water quality parameters or transportation duration. For the experimental evaluation, Walleye were transported either 0, 0.5, 3, or 5 hours and stress and mortality were evaluated up to 48 hours post-transport. Unlike, the field evaluation, the experimental evaluation used a staggered loading protocol to transport all Walleye on the same truck during the same day and allowed us to keep fish densities in each of the transportation truck compartments consistent throughout the experiment. Furthermore, in the experimental evaluation, I evaluated additional water quality parameters, not included in the field evaluation. In the experimental evaluation, total ammonia nitrogen, carbon dioxide, pH, and water temperature increased with transportation duration while the total alkalinity of the transport water decreased. Plasma cortisol and whole blood glucose concentrations of Walleye transported longer durations took longer to decline relative to those not transported. However, water quality parameters were not associated with changes in whole blood glucose and plasma cortisol concentrations. Despite increases in stress, Walleye mortality was low (2.5%) 48 hours after transportation. Understanding Walleye tolerance to transportation induced stress has the potential to enhance stocking programs by providing the opportunity for managers to make informed Walleye transportation practices. My second objective was to evaluate predation on Walleye, including whether consumed Walleye total length was related to predator total length, predator gape height, or the probability of predation, as well as assessed if length distributions varied among stocked, recaptured, and consumed Walleye. I also estimated cumulative consumption by a suite of piscivores (Largemouth Bass Micropterus salmoides, Smallmouth Bass M. dolomieu, Northern Pike Esox lucius, adult Walleye, and Muskellunge E. masquinongy) for two months post-stocking. During fall 2015-2017, 301 Walleye were recovered from 3,514 predator stomachs. Quantile regression models (mean = 50th percentile, maximum = 85th percentile, and minimum = 15th percentile) indicated that consumed Walleye total length was not related to predator total length or gape height (P > 0.05), but the probability of predation decreased by 0.02 for every 10 mm increase in Walleye total length. Length distributions indicated consumed Walleye were generally smaller, whereas recaptured Walleye tended to be larger than stocked fish. To estimate cumulative consumption of Walleye by Largemouth Bass, Northern Pike, and adult Walleye, I used Schnabel models to estimate predator population size and bioenergetics models to determine the biomass of consumed Walleye from stocking through ice-up (mid- November) during fall 2017 and 2018. Across years and systems, 3,272 predators were collected and 257 Walleye were recovered from predator stomachs. Northern Pike (0.12 Walleye per predator ± 0.32 SD) had the highest proportion of Walleye in their diets followed by Largemouth Bass (0.11 ± 0.30 Walleye per predator) and adult Walleye (0.04 ± 0.20 Walleye per predator). Largemouth Bass, Northern Pike, and adult Walleye collectively consumed between 2.4-27.2% of the stocked Walleye within two months of stocking, with higher proportions of smaller (<220 mm) Walleye in predator diets. In East Okoboji, highest proportions of age-0 Walleye in predator diets generally occurred 14 days after the most recent stocking event with the proportion of age-0 Walleye in predator diets decreasing thereafter. However, in West Okoboji, Northern Pike, adult Walleye, and Largemouth Bass had increasing proportions of age-0 Walleye in diets between stocking events. Collectively, results suggest that local piscivores have the potential to consume more than 27% of stocked age-0 Walleye within the first two months of stocking and that predation risk generally decreases with Walleye size. Thus, post-stocking predation can negatively influence Walleye stocking success, especially if the sizes of Walleye stocked have high predation risk. Hatchery propagation techniques, such as pellet-rearing, can result in impaired post-stocking feeding behavior of fishes. My third objective was to evaluate diet composition and diet shifts of Walleye. Specifically, my objective was to compare fall diets of wild and stocked Walleye by evaluating the proportion of empty stomachs as well as proportions of zooplankton, benthic invertebrates, and fish in diets. Percent similarity index values were also used to assess the percent similarity of wild and fingerling diets. In total, 590 Walleye were gastrically lavaged, with wild Walleye making up 9.7% and stocked Walleye making up 90.3% of the samples. The average proportion of empty stomachs differed between wild and stocked Walleye, with stocked Walleye having higher average (± 95% CI) proportions of empty stomachs (0.40 ± 0.10) compared to wild fish (0.15 ± 0.09). Proportion of empty stomachs and proportion of Walleye with zooplankton in diets decreased with days post-stocking. Stocked Walleye had a greater proportion of benthic invertebrates in their diet than wild Walleye whereas wild Walleye consumed more fish relative to stocked Walleye. However, the presence of zooplankton, benthic invertebrates, and fish in wild (TL = 129-215 mm) and fingerling (TL = 94-228 mm) Walleye diets were not related to Walleye total length. Finally, percent similarity index values for wild and stocked Walleye diets were highly variable and ranged from 0.0 to 67.9%. Collectively, my results suggest that fall stocked fingerling Walleye consume different prey items compared to their wild counterparts for up to 49 days post-stocking. Results pertaining to post-stocking Walleye diet composition may influence post-stocking survival. Numerous factors can independently and dependently influence the survival of stocked Walleye, including environmental conditions, predation, and Walleye total length, condition, and post-stocking diet composition. However, the relative effects of these factors on survival of stocked Walleye are challenging to evaluate and rarely assessed simultaneously. Thus, my fourth objective used mark-recapture techniques to evaluate the influence of predation, stocking environment, and Walleye physical characteristics (total length and condition at time of stocking) on apparent weekly survival from stocking until ice cover. Each fall (2015, 2016, and 2017), roughly 4,000 stocked Walleye were implanted with passive integrated transponder tags, stocked, and recaptured via boat electrofishing. Cormack-Jolly-Seber recapture models estimated that Walleye weekly apparent survival was negatively related to the weekly average proportion of Walleye recovered from predator diets (β = -2.86; 95% credibility interval = -5.69 to -0.17) as well as weekly average water temperatures (β = 0.09; 95% credibility interval = -0.08 to 0.20). At an average fall water temperature, mean Walleye apparent survival was 0.83 (95% credibility interval = 0.75 to 0.91) when no Walleye were recovered from predator diets and declined to 0.54 (95% credibility interval = 0.28 to 0.84) when Walleye comprised 60% of predator diets. Between 41-97% of stocked Walleye were lost to mortality from stocking through ice-up among the three years, indicating that the two months post-stocking is a critical period for survival. Our results suggest that post-stocking Walleye survival is most influenced by post-stocking predation rather than individual Walleye or environmental factors. Thus, strategies that minimize predation following stocking may result in the greatest improvements in Walleye post-stocking survival.

Probiotic nanoparticles for food

Chapter

Jan 2023

Nanotechnology is an area of science, engineering, and technology that deals with nanoscale dimensions and tolerances, specifically the manipulation of single atoms and molecules with diameters ranging from 1 to 100 nm. Carbon-based nanoparticles, ceramic nanoparticles, metal nanoparticles, semiconductor nanoparticles, polymeric nanoparticles, and lipid-based nanoparticles are some of the numerous types of nanoparticles that can be classified on the basis of their size, shape, physical, and chemical properties. Probiotics are live, nonpathogenic bacteria that are given to help maintain microbial balance, particularly in the gastrointestinal tract. These probiotics, which can be found in fermented foods and come in the form of capsules, pills, packets, or powders, are made up of lactic acid bacteria such as Lactobacillus and Bifidobacterium species, as well as Saccharomyces boulardii yeast. The applications of biosynthesis of nanoparticles from marine sources such as marine plants, marine animals, and marine microbes are discussed in this chapter. Probiotics can be found in a variety of forms, including dietary supplements, medicines, and medical foods. For more effective probiotic therapy for microbiota-related ailments, a greater understanding of the interplay between genetic, microbial, and environmental impacts within individuals is expected.

Recent Advances in Aquaculture Microbial Technology

Book

Oct 2022

Recent Advances in Aquaculture Microbial Technology emphasizes various topics on microbiology related technology for aquaculture development and discusses different types of microbiological applications, thus serving as an all-inclusive reference which consolidates microbial technologies adopted in the field. The book covers the history and development of microbial technology in aquaculture as well as aquaculture microbiology, diversity and the role of microbes in aquaculture systems. In addition, it presents the beneficial microbial communities in aquaculture and varying methods employed to study bacterial association in fish, microbes and fish diseases. This resource will help improve research experiments and accomplishments in the area of aqua-culturally relevant microbial technology, making it useful for researchers and scientists in the field.

Medicinal herbs and phytochemicals to combat pathogens in aquaculture

Article

Full-text available

Feb 2022
AQUACULT INT

The global production of aquaculture has grown rapidly and is dominated by China, Vietnam, and other East Asian countries. The use of antibiotics is widespread in the aquaculture industry but has been slowly decreasing as the benefits of medicinal herbs become clear. Various medicinal herbs are known to have excellent properties, such as antiviral, antibacterial, and antifungal activity; hormonal balancing; and physiological support (immune and digestive systems). The aim of this paper is to review the latest scientific information on the application of medicinal herbs in different aquaculture sectors, including marine, freshwater and crustacean culture, and the potential problems and recommendations for the application of medicinal herbs in aquaculture, to provide clues for the development of medicinal herbs for epidemic disease resistance of aquaculture industry in the future.

Effects of Stocking Transport Duration on Age-0 Walleye

Article

Jun 2021

Fish hatcheries are generally not adjacent to stocking locations. Thus, hatchery fish undergo transportation processes for variable durations that can result in changes in water quality, fish physiology (e.g., whole blood glucose and plasma cortisol), and reduced survival. Walleye Sander vitreus are commonly stocked throughout North America with variable stocking success, possibly due to altered physiological responses associated with changes in water quality parameters during transportation. We hypothesized increased transport duration would be associated with increases in water temperature, carbon dioxide, and total ammonia nitrogen and decreases in pH and total alkalinity. We also hypothesized that increases in carbon dioxide, water temperature, un-ionized ammonia, and total ammonia nitrogen would be positively related with Walleye whole blood glucose and plasma cortisol concentrations. Walleye were transported for either 0, 0.5, 3, or 5 h and whole blood glucose and plasma cortisol concentrations and mortality were evaluated for 48 h posttransport. Total ammonia nitrogen concentrations, carbon dioxide, pH, and water temperature increased with transportation duration while total alkalinity decreased. Plasma cortisol and whole blood glucose concentrations of Walleye transported for longer durations took longer to decline relative to those not transported. Water quality parameters were not associated with changes in Walleye whole blood glucose and plasma cortisol concentrations, but they were negatively related with time since transport (P < 0.05). Despite increases in stress, mortality was low (2.5%). Overall, we found evidence to support our hypotheses regarding reduced water quality associated with increasing transport duration. Finally, whole blood glucose and plasma cortisol concentration of Walleye that were transported were similar to those not transported, suggesting handling procedures before transportation could play a significant role in physiological responses measured after transportation. Further, evaluation of stocking procedures aimed at decreasing handling during the loading process could enhance stocking protocols. Elevated concentrations of whole blood glucose and plasma cortisol following transport could make recently stocked Walleye more susceptible to the effects of other environmental factors such as starvation, predation, and disease, all of which could result in increased mortality rates after stocking.

Odontogenic hamartomas in cultured angelfish (Pterophyllum scalare)

Article

Jan 2021
J EXOT PET MED

Background Odontogenic tumors present diverse clinical and histopathological behaviors that range from benign odontoma or hamartoma lesions to malignant tumors. In angelfish Pterophyllum scalare, findings of tumorous masses have been reported in the frontal region of the mouth, encompassing both the maxilla and mandible. Histologically, oral tumors have been characterized as angelfish lip fibroma or ameloblastoma. Methods In this report, we describe the occurrence of a compound odontoma/hamartoma in 60 angelfish from a population of 300, all of which were collected from a Mexican ornamental fish farm. Results All fish presented a tumor-like mass on the rostral part of the mouth. Histological analyses revealed the tumor-like mass was covered by a hyperplastic stratified squamous epithelium, with fully differentiated denticles in various states of organization, immersed among normal dental tissues and showing a mild disorganized pattern. Radiograph analysis revealed radiopaque denticles in a radiolucent protuberance. Bacterial and viral isolation procedures and electron microscopy analysis revealed no presence of these microorganisms. Conclusion and clinical relevance Although findings of odontogenic tumors in the mouth of angelfish are reported as sporadic, our study detected odontogenic mouth tumors in 60 angelfish, but the possible cause of alteration is not yet clarified. Further research is needed to clarify pathogenesis and to identify possible genetic abnormalities.

Skin and stinger bacterial communities in two critically endangered rays from the South Atlantic in natural and aquarium settings

Article

Full-text available

Dec 2020

Bacterial communities of two critically endangered rays from the South Atlantic, the butterfly ray (Gymnura altavela) and the groovebelly ray (Dasyatis hypostigma), were described using 16S rRNA gene metabarcoding. The study characterized the bacterial communities associated with (i) G. altavela in natural (in situ) and aquarium (ex situ) settings, (ii) skin and stinger of G. altavela, and D. hypostigma in aquaria, and (iii) newborns and adults of D. hypostigma. The results revealed potentially antibiotic-producing bacterial groups on the skin of rays from the natural environment, and some taxa with the potential to benefit ray health, mainly in rays from the natural environment, as well as possible pathogens to other animals, including fish and humans. Differences were observed between the G. altavela and D. hypostigma bacteria composition, as well as between the skin and stinger bacterial composition. The bacterial community associated with D. hypostigma changed with the age of the ray. The aquarium environment severely impacted the G. altavela bacteria composition, which changed from a complex bacterial community to one dominated almost exclusively by two taxa, Oceanimonas sp. and Sediminibacterium sp. on the skin and stinger, respectively.

Skin and stinger bacterial communities in two critically endangered rays from the South Atlantic in natural and aquarium settings

Article

Full-text available

Nov 2020

Bacterial communities of two critically endangered rays from the South Atlantic, the butterfly ray (Gymnura altavela) and the groovebelly ray (Dasyatis hypostigma), were described using 16S rRNA gene metabarcoding. The study characterized the bacterial communities associated with (i) G. altavela in natural (in situ) and aquarium (ex situ) settings , (ii) skin and stinger of G. altavela, and D. hypostigma in aquaria, and (iii) newborns and adults of D. hypostigma. The results revealed potentially antibiotic-producing bacterial groups on the skin of rays from the natural environment, and some taxa with the potential to benefit ray health, mainly in rays from the natural environment, as well as possible pathogens to other animals, including fish and humans. Differences were observed between the G. altavela and D. hypostigma bacteria composition, as well as between the skin and stinger bacterial composition. The bacterial community associated with D. hypostigma changed with the age of the ray. The aquarium environment severely impacted the G. altavela bacteria composition, which changed from a complex bacterial community to one dominated almost exclusively by two taxa, Oceanimonas sp. and Sediminibacterium sp. on the skin and stinger, respectively.

Applications of microbially derived nanomaterials in disease prevention and treatment

Chapter

Jan 2023

Fishes play a pivotal role in fulfilling the vast demand for food virtually all over the world. Fish is a major source of large amount of healthy protein and many nutrients among the naturally available foods. Possibility of diseases and environmental contamination are major threats to the aquaculture and fish farming industries. All fishes carry parasites and pathogens from their natural habitat. As such, novel approaches are required to effectively control parasites and pathogens. Nanoparticles have tremendous potential in aquaculture owing to their unique properties such as very large “surface area to volume” aspect ratios, lower melting point, specific optical properties, and mechanical strengths as compared to their bulk or higher-scale counterparts. The current book chapter covers the possible uses of nanotechnological approaches for the control of fish diseases in aquaculture. Besides, it gives a general idea about different fish diseases and the conventional methods for controlling the diseases.

Cyprinid herpesvirus-2 (CyHV-2): a comprehensive review

Article

Sep 2020

Cyprinid herpesvirus‐2 (CyHV‐2) is a linear double‐stranded DNA virus in the genus Cyprinivirus of family Alloherpesviridae. The virus is known to be highly pathogenic to ornamental goldfish (Carassius auratus), crucian carp (C. carassius) and Gibel carp (C. auratus gibelio), and also to the hybrids of goldfish and other carps. Cyprinid herpesvirus‐2, having the smallest genome (290.3 kb) among Cyprinivirus, causes herpesviral hematopoietic necrosis disease (HVHND) that results in huge economic losses in aquaculture industry as the disease can cause high mortality (50–100%) among the affected fish. The disease was initially reported as the cause of epizootics in juvenile goldfish of Japan during 1992 and 1993. To date, this disease has been reported around the world including Europe, North America, Oceania and Asia. Huge economic losses due to the CyHV‐2 infection among cultured gibel carp in China, during 2011–2012, mass mortality in crucian carp during 2012 in Italy, 95% mortality in goldfish during 2014 in France, 85% mortality in goldfish during 2016 in Poland had been reported. Strategies for controlling the spread of CyHV‐2 are thus urgently required to limit economic damage. Furthermore, the review will shed light on lacunae in current knowledge as well as on the perspectives that merits further investigations on CyHV‐2 research. The paper forms the first comprehensive overview of CyHV‐2 causing a serious economically significant fish disease and, will be helpful for the researchers to get all related information from a single manuscript.