Determination of Benthic Soil Conditions Using Nematodes: Nematode FoodWeb Conditions of Fish Ponds in the Lincoln and Desha Counties of Arkansas

We determined the health status of similar channel catfish (Ictalurus punctatus) ponds in Lincoln and Desha counties of Arkansas, using the nematode soil food web condition as our reference point. Soil nematodes were categorized into colonizer-persister (cp) groups, based on their life course characteristics e.g sensitivity to environmental changes, body size, etc. These cp groups represent different components of the soil food web, which in turn were indicators of soil conditions. Benthic soil samples were collected at four week intervals over a 4-month period, from 6-ponds in each county. The nematodes were extracted according to standard methods and the recovered nematode taxa grouped according to their cp values. The product of each nematode taxon was determined (mean number of individuals x cp value) and the sum of all members of a cp group constituted the biomass produced by that cp group. Nematodes of the cp-3 and cp-4 groups dominated in biomass productivity in ponds for both counties. These groups of nematodes represent structured components of a food web and therefore a healthy ecosystem. Lincoln county ponds had higher cp-3 and cp-4 biomass likely due to slightly less acidic conditions while Desha county ponds had a greater biomass of plant-parasitic nematodes. It was also found that free-living nematodes tolerate more acidic conditions than plant-parasitic nematodes, though this could also be related to more root tissues. Nematode biomass calculations could be useful in determining benthic soil food web conditions, which may provide a simple way of assessing environmental conditions and changes in Arkansas catfish ponds

CHANNEL CATFISH INDUSTRY IN THE USA AND THE OFF-FLAVOR PROBLEM

Prikazani su povijest i razvoj tehnologije gojidbe kanalnog soma u ribnjacima te statistički podaci o proizvodnji, doradi i vrijednosti proizvoda u tijeku posljednjih 15 godina. Povećanje potrošnje u pučanstvu te sadašnje niske cijenež žitarica i soje povoljni su čimbenici za daljnje povećanje proizvodnje. Stalan razvoj industrije potiče nekoliko čimbenika: pionirski napori uzgajivača, istraživanja na sveučilištima i u državnim istraživačkim centrima od kojih neki imaju brojne pokusne ribnjake, rad kooperativne savjetodavne službe za ribnjačare, aktivnost udruga uzgajivača soma, suvremeni marketing, visoku kvalitetu proizvoda dorade i vertikalno povezivanje industrije. Neprikladna okusno-mirisna kakvoća soma uzrokovana metabolitima algi jedna je od glavnih poteškoća u industriji. Spomenuti su najvažniji rodovi algi koje proizvode takve metabolite, pojave mirisno-okusne neprikladnosti u drugih riba i u akumulacijama za pitku vodu, te sadašnji sustav sprečavanja dolaska kontaminirane ribe na tržište. Od nepoželjnih metabolita algi najvažniji su hlapljivi alkoholi geosmin i 2-methylisorborneol (MIB). Naglašena je potreba jeftinijih i bržih metoda određivanja tih metabolita. Istraživanja na Sveučilištu Arkansas u Pine Bluffu, SAD, o kontroliranju nepoželjnih vrsta algi u pokusnim ribnjacima s pomoću bijelog glavaša (Hypophthalmichthys molitrix Val.) i tilapija u kavezima pokazala su da taj pristup obećava uspješnost.The history, the production technology in channel catfish pond farming industry as well as the statistical data on production, processing and product value during past 15 years are presented. The trend of increasing consumption by the population and the presently low prices of grain and soybeans are conductive to further expansion of production. The steady growth of the industry is stimulated by several factors: innovative efforts by farmers, research at the universities and at government institutions some of which have numerous experimental ponds, cooperative extension service for farmers, modern marketing, activities of catfish farming associations, high quality of products from processing plants and vertical integration. The off-flavor in catfish caused by algal metabolites is a major problem in the industry. Genera of algae producing such metabolites, their accumulation in other fish and occurrence in drinking water reservoirs as well as the current emphasis on preventing the entrance of off-flavor contaminated catfish onto the market were reviewed. The main undesirable algal metyabolites are volatile alcohols geosmin and 2-methylisoborneol (MIB). The need for less expensive and quick methods of identifying major off-flavor compounds was pointed out. Research at the University of Arkansas at Pine Bluff, USA, on control of off-flavor algae in experimental ponds by filter-feeding silver carp (Hypophthalmichthys molitrix Val.) and tilapias confined in cages showed this approach to be rather promising