Marine Parasitology
is an important field in aquatic science. Because of its close linkeage to other fields in marine sciences such as fisheries, mariculture, fish ecology and environmental monitoring, marine parasitology should be seen in the context of other marine science disciplines (see Marine Science Special Training Course-MST). Fish parasites play a major
role in marine biodiversity, infecting hosts at all different trophic
levels. The growth of marine aquaculture, concerns about the effects of
pollution on fish health, and the possible use of parasites as
biological indicator organisms has led to a steady increase in interest
in this topic.
Fish and
fisheries products are important sources of protein and contribute a
great deal to available food resources worldwide. Over-fishing and
environmental degradation are already threatening most of the larger
fish stocks, and a further increase in fisheries production seems to be
dependent on the cultivation of aquatic organisms within semi-extensive
and intensive mariculture. An intensive culture leads to an increasing
risk of infection by disease causing agents, such as fungi, viruses,
bacteria and parasites.
Grouper mariculture farm
Parasites
are an integral part of every ecosystem,representing a major factor in global biodiversity. Host-parasite
checklists suggest that on average, there are at least 3-4 metazoan
parasites per studied marine fish species within a specific environment.
This led to a conservative estimate, by Klimpel, Palm, Seehagen & Rosenthal
(2001), of 20,250 to 43,200 marine metazoan fish parasites, calculated on
the basis of the 13.500 currently known fish species that inhabit brackish
or marine waters. Fish parasites clearly constitute a major part of the
living animal species within the world’s oceans.
Parasites in marine fish
are of public concern if they are found dead or alive
within food products that are intended for human consumption. Besides
infection from living parasites, pathogens that are already dead or
their remains within the fish tissue might harm the consumer by causing
allergic reactions. The disgusting appearance of heavily parasitized
fish can prevent them from being sold on local and international markets
as their presence in the musculature can offend potential consumers.
Thus, parasites can significantly contribute to financial losses for the
fisheries industry.
Worms in the fish musculature
Parasites as disease causing agents
can have various effects on the fish’s health. They can infest all
organs, and depending on the site and intensity of infestation, they are
more or less harmful. A high number of negative consequences does not
only influence the fish itself but is assumed to also have a larger
impact on whole ecosystems. Interestingly, disease causing agents and
parasites have not yet been included within models to monitor the
population dynamics of fish stocks in the field of fisheries biology,
the basis of the actual management of commercially important marine fish
stocks worldwide.
Worms in the fish liver
Fish
parasites are important biological indicators
to describe migration patterns of fish stocks, trophic and
phylogenetic interactions as well as pollution and eutrophication. Within
fisheries biology, fish parasites were successfully used to separate
different fish stocks. Long-living species such as endoparasitic helminths
can give information on the seasonal migrations of their hosts and migration
habits of different age groups, while short-living species, combining a
direct life cycle and high reproduction rates such as protozoan
ectoparasites and monogenean trematodes can give information on
environmental conditions. It can be expected that with an increasing
knowledge of the species diversity, life cycle biology and ecological needs
of the various marine fish parasites, further information becomes available
for their potential use as biological indicators. This tool will surely
provide a better ecological understanding of the whole marine ecosystem.
Marine fish
parasitology contributes to various scientific disciplines.
Zoological studies, such as those dealing with the taxonomy,
classification, morphology and phylogeny of marine fish parasites are
still needed, if our attempts to provide a natural animal system
including the fish parasites are to be successful. Besides utilizing
classical metho-dologies such as morphometrical studies or using
scanning and transmission electron microscopy, modern techniques in
biochemistry and molecular biology offer a wide range of new
applications to better understand the phylogenetical relationships as
well as the morphological and physiological characteristics of the
different species. In addition, topics connecting the fish hosts with
their parasites, such as host-parasite co-evolution or host parasite
interactions (host and site specificity, immunology, pathognicity) have
not yet been fully explored. Even the coelacanth Latimeria
chalummnae Smith, 1939 is known to harbor several different marine
fish parasites. Therefore, modern marine fish parasitology is firmly
anchored within the different biological disciplines, and can offer
various topics for integrated research activities.
Phenogram depicting the genetic differences (upon
pairwise comparison) among the fish parasitic nematodes Pseudoterranova
spp. for the entire ITS rDNA sequence (Zhu et al. 2002)