BACTERIOLOGICAL PROPERTIES OF MARINE WATER IN ADRIATIC FISH FARMS: ENUMERATION OF HETEROTROPHIC BACTERIA

Akvakultura je jedna od grana proizvodnje hrane, s izuzetnim razvojem. Povećana primjena hrane u akvakulturi, uz moguće organsko onečišćenje generalno vodi ka narušavanju kvalitete vode. Problemi narušene kvalitete vode vezani su uz fizikalne i kemijske čimbenike, kao i narušavanje mikrobiološke kvalitete vode. Heterotrofne bakterije imaju značajnu ulogu u procesu razgradnje organske tvari u vodenom okolišu i pokazatelj su procesa eutrofikacije. U ovom su radu prikazana naša iskustva i spoznaje o bakteriološkim svojstvima morske vode u uzgajalištima lubina (Dicentrarchus labrax L., 1758) uzduž istočne obale Jadranskog mora, s ciljem određivanja broja heterotrofnih bakterija u morskoj vodi primjenom dvije metode i dvije temperature inkubacije. Primijenjene su dvije metode za prebrojavanje heterotrofnih bakterija u morskoj vodi: supstrat SimPlate® test i metoda širenja uzorka po podlozi s uporabom uobičajenih umjetnih hranjivih podloga (Marine agara i Tryptic Soy agara s dodatkom NaCl), kao i dvije temperature inkubacije (22ºC i 35ºC). Rezultati analize bakterioloških svojstava morske vode u jadranskim uzgajalištima upućuju da je određivanje broja heterotrofnih bakterija u morskoj vodi ovisno o primijenjenoj temperaturi i mediju za brojanje. Pri tome je temperatura inkubacije od 22°C pogodnija za rast heterotrofnih bakterija iz morske vode, a SimPlate test daje veće vrijednosti broja heterotrofnih bakterija. Rast vrijednosti broja heterotrofnih bakterija tijekom istraživanja upućuju na moguće narušavanje mikrobiološke kvalitete morske vode u jadranskim uzgajalištima te na potrebu redovitog monitoringa kvalitete morske vode.Aquaculture is currently one of the fastest growing food production sectors in the world. Increase in nutrients and organic wastes lead to general deterioration of water quality. The problem of water quality is associated with both physical and chemical factors, as well as microbiological water quality. Heterotrophic bacteria play an important role in the process of decomposition of organic matter in water environment and indicate eutrophication process. Here we present our experience and knowledge on bacterial properties of marine water in the Adriatic fish farms with European sea bass (Dicentrarchus labrax L., 1758), with an emphasis on enumeration of heterotrophic bacteria in marine water. We applied two temperatures of incubation, as well as two methods for enumeration of heterotrophic bacteria: substrate SimPlate® test and spread plate method on conventional artificial media (Marine agar and Tryptic Soy agar with added NaCl). The results of analysis of bacteriological properties of marine water in the Adriatic fish farms showed that enumeration of heterotrophic bacteria in marine water depends on the applied incubation temperature and media for enumeration. At the same time, the incubation temperature of 22C favours more intense growth of marine heterotrophic bacteria, whereas a SimPlate test gives higher values of heterotrophic bacteria. Volatile values of heterotrophic bacteria during this research indicate a possible deterioration of microbiological water quality in the Adriatic fish farms and a need for regular monitoring of marine water quality

Skin Culturable Microbiota in Farmed European Seabass (Dicentrarchus labrax) in Two Aquacultures with and without Anibiotic Use

This study examined culturable skin microbiota that was associated with farmed European seabass (Dicentrarchus labrax). Healthy European seabass were sampled during summer commercial harvest from one conventional fish farm where antibiotics are used, and from another practicing a certified antibiotic-free fish aquaculture. Physicochemical and microbiological analysis of seawater and sediment were performed, as well as determination of culturable bacteria, including Vibrio, from skin swabs of European seabass and seawater and sediment at both farms. Samples were processed for isolation of bacteria and their characterization by molecular and antibiotic susceptibility tests. In both fish farms, most of the bacteria that were identified in the skin belonged to the genera Pseudomonas and Vibrio. Some of the microbiota that were identified are known to be pathogenic to fish: V. alginolyticus, V. anguillarum, and V. harveyi. Vibrio strains showed higher resistance to certain antibiotics compared to previous studies. This study provides, for the first time, information on the culturable skin bacteria that is associated with healthy European seabass under culture conditions with and without the use of antibiotics. This information will be useful in assessing how changes in culturable microbiota may affect the health of farmed European seabass, indicating a potential problem for fish health management during disease outbreaks

Application of Calcified Structures in Fish as Indicators of Metal Exposure in Freshwater Ecosystems

Although there are common and well-established bioindicator organisms and tissues, there is still a need for reliable and sensitive bioindicators in aquatic environments. In the present pilot study, calcified structures in fish were applied as indicators of metal exposure in combination with commonly used fish soft tissues and intestinal parasites, therefore comprising short- and long-term indicators. Patterns of metal accumulation and distribution in soft (muscle, liver) and hard (scales, otoliths) tissues of brown trout (Salmo trutta Linnaeus, 1758) and their intestinal parasites, acanthocephalans (Dentitruncus truttae Sinzar, 1955), from the Krka River influenced by industrial and municipal wastewaters were estimated and compared. Most elements had higher levels in acanthocephalans, scales and liver than muscle and otoliths, possibly reflecting differences in metal uptake routes, tissue function and metabolic activity. Despite the recorded differences in metal contents, all applied bioindicators reflected environmental conditions in a similar way, indicating higher levels of most elements in fish from the contaminated rather than from the reference site. Acanthocephalans were confirmed as sensitive bioindicators due to effective metal accumulation capacity, while the combination of soft and hard tissues provided extended temporal information on metal exposure. Wastewater impact was evidenced as moderate metal pollution by all applied indicators and pointed to present but also long-term disturbances in the Krka River and the importance of continuous monitoring and protective actions