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Aquaculture is arguably the fastest growing industry in global food animal production, but diseases and related mortalities are the main factors that determine the limits of production volume. Fish in aquaculture systems are susceptible to infectious agents as they are kept in a densely populated and often physically restricted environment. Genus Aeromonas include well-known pathogens, and the member Aeromonas veronii has been reported to cause diseases in both humans and animals, either as primary infection or as mixed infection with other pathogens. This study describes a low mortality epizootic caused by Aeromonas veronii biovar veronii in European seabass (Dicentrarchus labrax) farmed in the Aegean Sea. The gills, kidneys and livers of moribund fish were pale. Erythema, haemorrhage and superficial ulcerative lesions were detected on the skin. In addition, petechial haemorrhage was observed on the tongue, maxilla and operculum. The spleen was enlarged and multiple abscesses were detected in both the liver and the spleen. Granulomas were observed in the spleen and the kidney. Some fish had skin depigmentation, ecchymosis in the liver and a bloody exudate in the abdominal cavity. The intestinal walls were lined with a clear yellowish fluid. Twenty-nine motile, Gram-negative bacterial isolates were obtained from the internal organs of diseased fish. According to morphology, biochemical properties and 16S rRNA gene sequencing results, all isolates were identified as Aeromonas veronii bv. veronii. All isolates were resistant to amoxicillin and ampicillin but, only intermediate resistant to sulfamethoxazole/trimethoprim.

Artemia franciscana metanauplii widely is being used in cultured marine species. The aim of this study was to evaluate the effect of feeding with two marine and two freshwater microalgae as feed alone or in combination on survival, growth, and fatty acid composition of A. franciscana metanauplii and on predominant bacterial species of the rearing water. Five microalgae diets were used for feeding: Amphora viridis (AV), Chlamydomonas reinhardtii (CR), Chlorella vulgaris (CV), and Dunaliella salina (DS) and a combination of four microalgae (MX diet). Artemia franciscana fed AV, DS, and MX diets showed higher survival than that fed CR and CV diets. MX group showed higher total length among groups (P < 0.05). Total n-3 fatty acid content was higher in the Artemia franciscana fed MX group, whereas total n-3 HUFA levels were found significantly higher in Artemia franciscana fed DS and AV diet (P < 0.05). The bacterial load of the rearing water was significantly decreased with the use of CV; therefore, the CV diet might be suggested to be used in Artemia franciscana grow-out for reducing bacterial proliferation. According to 16S rRNA gene sequencing results, four different bacterial species including Carnobacterium maltaromaticum, Pseudomonas stutzeri, Pseudoalteromonas sp., and Vibrio sp. species were found predominantly in the rearing water of Artemia franciscana.

Aims We performed in silico analysis of CRISPRcas loci from Tenacibaculum maritimum, evaluated spoligotyping as a subtyping method and genotyped uncharacterized Turkish isolates from European sea bass by multilocus sequence typing (MLST). Methods and results Spoligotyping was performed with primers designed to allow amplification and sequencing of whole CRISPR-arrays from 23 T. maritimum isolates. Twenty-three completed/draft genomes were also downloaded from the NCBI database and analysed. MLST of Turkish isolates was achieved with a well-established 7-gene scheme. Tenacibaculum maritimum genomes carry a structurally complete but partially defective class II CRISPRcas locus due to known amino acid substitutions in encoded Cas9 proteins. Our spacer identification suggests that the host range of bacteriophage P2559Y and Vibrio phage nt-1 include T. maritimum and that the most recurrent infection recorded by isolates has been with Tenacibaculum phage PTm5. Thirty-eight isolates with this CRISPRcas locus belonged to 25 spoligotypes and to 24 sequence types by MLST, respectively. According to MLST, T. maritimum isolates from Turkey are most related to previously defined sequence types ST3, ST40 and ST41 isolates from Spain, Malta and France. Conclusions The evaluated spoligotyping offers discriminatory power comparable to MLST. Significance and impact of the study Spoligotyping has potential as a quick, easy and cheap tool for subtyping of T. maritimum isolates.

In this study, the phytoplankton composition and some water quality parameters of cultured sea bass (Dicentrarchus labrax, L., 1758) earthen ponds were investigated in Muğla Province, Turkey. Sea bass which production significantly increased since the 1980s, is accepted as one of the popular species in the Mediterranean region. Samples were collected from the fish farm when algal blooms are observed in May 2017, from 6 sampling points, including the main drainage, clean water, and 4 earthen ponds. In total 31 taxa belonging to 7 divisions as Bacillariophyta (13), Charophyta (1), Chlorophyta (7), Cryptophyta (2), Cyanobacteria (3), Euglenozoa (4), and Ochrophyta (1) of phytoplankton were determined. Recorded species of the phytoplankton indicated organic pollution at the studied earthen ponds. Excessive algal blooms, particularly caused by blue-green algae, pose a great threat to all fish farm organisms by causing massive fish deaths in aquaculture ponds. The toxin-producing Cyanobacteria Microcystis aeruginosa (Kütz.) Kützing and Merismopedia glauca (Ehr.) Kützing were found often in water samples. Since pond management is essential for a productive fish farm obtained results indicated that the first step to enhancing good quality products in the aquaculture sector should have the sustainable monitoring of phytoplankton by farmers and adequate supplying water.

The aim of the study was to determine a considerable level of mortalities occurred in rainbow trout fry (Oncorhynchus mykiss) cultured in a research hatchery located in Marmara Region/Turkey. Totally 18 individuals (1-8 g) were investigated by using bacteriological and mycological methods. The affected fish showed skin darkening, prolapses and fungal mats at the base of the fins. According to morphological and biochemical characteristics of the isolates, all of them were identified as Aeromonas sobria. Saprolegnia sp. was also observed in squash preparations of the skin. All isolates were determined to be sensitive against florfenicol, enrofloxacin and ciprofloxacin. Histopathologically, vacuolar degeneration, haemorrhage and hyperaemia in the liver, tubular necrosis, periglomerular edema, and multifocal melanomacrophage deposits in the kidney and depletion of white pulp in the spleen were determined. Distal type epithelial cells hyperplasia was also observed in the gills. In diseased fish, motile Aeromonad septicaemia was described and Saprolegnia sp. was also detected in fins and skin lesions but it was considered to be a secondary infection.

A massive die-off of benthic suspension feeders (BSF) covered by large amounts of sediments was observed along Prince Islands coasts (north-eastern Sea of Marmara) in August 2015. Alcyonarians, pennatulaceans, bivalves and sponges were severely affected. Many BSF probably died from burial and clogging of their feeding and respiratory apparatus. Of the gorgonian colonies, 66 ± 34% (mean ± SD) were dead, while 15 ± 16% (mean ± SD) displayed recent necrosis on the colony surface. In addition, histopathological and microbial examinations of the affected gorgonians and gold corals (Savalia savaglia) suggest that stress caused by sedimentation made them vulnerable to exploitation by consistently isolated opportunistic microorganisms. We isolatedVibrio splendidusandVibrio neptuniusfrom diseased gold coral colonies, but the bacterial isolates obtained from gorgonians could only be identified to genusVibriolevel. The presumably artificially introduced fungusMucor circinelloideswas common on both gold coral and gorgonians. This mould and opportunistic bacteria may have colonized BSF by taking advantage of low oxygen levels leading to impaired coral immune responses and thereby exacerbated the BSF mortality. Construction and landfill operations at Yassıada seem to be the greatest contributor to the observed sedimentation, as shown by silicate concentrations in nearby waters. These observations imply that preventive measures are necessary when construction operations take place in the vicinity of sensitive marine habitats.

Marmara Bölgesi'nde bulunanBüyükçekmece Baraj Gölü, İstanbul'un altı ana rezervuarının üçüncü en büyük sukaynağıdır. Güvenli bir içme suyu kaynağı olarak kullanılır. Bu çalışmada Eylül2012-Mayıs 2013 döneminde Büyükçekmece Baraj Gölü tatlı su balık türlerininparazit faunası araştırılmıştır. Gölden balık numunelerinin toplanması içinsolungaç ağları kullanılmıştır. Balık örnekleri fiberglas tanklarda laboratuvara taşınmış ve parazitolojik inceleme yapılıncaya kadarcanlı tutulmuştur. Diseksiyon sırasında vücut boşluğu, tüm iç organlar,solungaçlar, gözler, deri ve yüzgeçler incelenmiştir. Dokuz balık türüne aitolan toplam 273 balık örneği incelenmiş ve enfeste bireylerde 11 parazit türübulunmuştur. Ancylodiscoides vistulensis,Tetraonchus monenteron, Paradiplozoon homoion, Caryophyllaeus laticeps, Bothriocephalus acheilognathi, Raphidascaris acus and Eustrongylides excisus tür seviyesindeteşhis edilmiştir. Enfeste bireylerde Trichodinaspp., Dactylogyrus spp., Ergasilus spp. ve Glochidia larvası cinsseviyesinde teşhis edilmiştir. Monogeneaen yaygın parazit grup olarak tespit edilmiştir. Eustrongylides excisus ise farklı balık türlerinde en yaygınparazit olarak gözlenmiştir., Büyükçekmece Dam Lake, locatedin the Marmara Region, is the third largest water resource of the six mainreservoirs of Istanbul. It is used as a safe drinking water source. In thisstudy, the parasitic fauna of the freshwater fish species in Büyükçekmece DamLake was investigated during the period of September 2012-May 2013. Gill netswere used for the collection of fish specimens from the lake. The fishspecimens were transported to the laboratory in fiberglass tanks and they were kept alive untilparasitological examination. During the dissection, the body cavity, allinternal organs, the gills, the eyes, the skin, and the fins were examined. Atotal of 273 fish specimens belonging to nine fish species were examined and 11 parasite species were found in infestedindividuals. Ancylodiscoides vistulensis,Tetraonchus monenteron, Paradiplozoon homoion, Caryophyllaeus laticeps, Bothriocephalus acheilognathi, Raphidascaris acus and Eustrongylides excisus were identifiedto the species level. Trichodinaspp., Dactylogyrus spp., Ergasilus spp. and Glochidia larvae wereidentified the genus level in infested individuals. Monogenea was determined asthe most common parasite group. Eustrongylidesexcisus was also observed as the most prevalent parasite in as different fishspecies.

This study aims to determine the cause of mortalities in smooth-hound sharks (Mustelus mustelus, Linnaeus 1758) under stressful conditions from a marine aquarium in Turkey. Moribund smooth-hound sharks externally had haemorrhages on various body parts, especially the pectoral fins and certain areas of their skin. A pale liver and spleen pseudo-tubercles were the main pathological findings internally. For bacteriological examination, samples were taken from visceral organs and blood and streaked onto marine agar (MA) plates which were incubated at 22°C for 72 hours. Gram-negative motile rods that displayed a bipolar staining were isolated from several tissues, including the spleen, kidney and liver. According to their morphological and biochemical characteristics as well as 16S rRNA gene sequencing, these isolates were identified as Photobacterium sanguinicancri. Therefore, it was concluded that photobacteriosis was responsible for this disease outbreak in aquarium-kept smooth-hound sharks. According to the literature survey this is the first report on describing photobacteriosis caused by Photobacterium sanguinicancri in this shark species., Bu çalışma, Türkiye'deki bir deniz akvaryumunda stresli koşullar altında bulunan tazı köpekbalıklarında (Mustelus mustelus, Linnaeus 1758) meydana ölümlerin nedenlerinin belirlenmesini amaçlamaktadır. Eksternal olarak ölmek üzere olan tazı köpekbalıklarının çeşitli vücut kısımlarında, özellikle göğüs yüzgeçlerinde ve deride belirli bölgelerinde kanamaları vardı. İnternal olarak soluk karaciğer ve dalakta psödotüberküller ana patolojik bulgulardı. Bakteriyolojik inceleme için iç organlardan ve kandan örnekler marine agar (MA) içeren petrilere ekimler yapılmış ve 22°C'de 72 saat inkübe edilmiştir. Bipolar boyama özelliği gösteren gram negatif hareketli basiller dalak, böbrek ve karaciğer dahil olmak üzere çeşitli dokulardan izole edilmiştir. Morfolojik ve biyokimyasal özelliklerine ve 16S rRNA gen dizilimine göre, bu izolatlar Photobacterium sanguinicancri olarak tanımlandı. Bu nedenle, akvaryumda tutulan tazı köpekbalıklarında bu hastalık salgınına photobacteriosis’in neden olduğu sonucuna varılmıştır. Literatür araştırmasına göre, bu köpekbalığı türünde Photobacterium sanguinicancri'nin neden olduğu photobacteriosis'i tanımlayan ilk rapor budur.

Live-feed is indispensable to commercial fish larviculture. However, high bacterial loads in rotifers could pose a biosecurity risk. While this may be true, live-feed associated bacteria could also be beneficial to fish larvae through improved feed utilization or pathogen inhibition following host microbiota modification. The study objective was to elucidate the largely unexplored microbiota of rotifers propagated on five different diets through bacterial community profiling by 16S rRNA gene amplicon sequencing. Investigated rotifer samples had a median observed alpha-diversity of 338 ± 87 bacterial species. Alpha- and Gamma-Proteobacteria dominated the rotifer microbiota followed by members of classes Flavobacteriia, Cytophagia, Mollicutes, Phycisphaerae and Bacteroidia. Different diets significantly altered the bacterial communities associated with rotifers according to PERMANOVA test results and beta dispersion calculations. A common core rotifer microbiome included 31 bacterial species present in relative abundances over 0.01%. We discuss the functional role of some microbiome members. Our data suggested the presence of several known fish pathogens in stock rotifers. However, we found no evidence for increased loads of these presumptive taxa in propagated live-feed rotifers during this field trial.

Summary In order to investigate the unclear status of albacore (Thunnus alalunga) reproduction in the Eastern Mediterranean Sea, the stages of oogenesis from 129 females (64.0 and 83.5 cm fork length) were collected and analysed between April and August for the years 2002 and 2008. Fish were captured by commercial vessel gillnets. Based on histological examination of the ovaries, a total of seven ovarian developmental stages were identified: (i) perinucleolar, (ii) phase of early lipid enrichment, (iii) early vitellogenesis, (iv) late vitellogenesis, (v) migratory nucleus, (vi) pre-hydrated and (vii) hydrated oocyte phase. Data on the monthly gonadosomatic index and the results of the histological analyses indicate that in the region the female T. alalunga mature in May. The spawning stage is predominant in June, reaching a maximum in July. The evidence reported here indicates that size at first sexual maturity for females was lower for the Mediterranean albacore stock than for the Pacific and Atlantic stocks.

Bu calisma, Turkiye'de bir deniz akvaryumunda bulunan humpback red snapper ( Lutjanus gibbus ) ve golden trevally ( Gnathanodon speciosus ) baliklarinin olum nedenlerinin belirlenmesi amaciyla yapilmistir. Hasta baliklarda, ust ve alt cenelerde yaygin hemoraji, yuzeysel ve ulseratif deri lezyonlari, kuyruk yuzgecinde erime ve solungaclarin solgun oldugu gozlemlendi. Ic bakida, periton boslugunda berrak sivi birikmesi ve solgun karaciger tespit edildi. Izole edilen bakteriler morfolojik, fizyolojik, biyokimyasal ozelliklerine ve API 20E sonuclarina gore Vibrio harveyi olarak tanimlandi. Bu bakteriyel tanimlamalar 16S rRNA gen dizisi analizi ile de dogrulanmistir. Izolatlarin sulfametoksazol/trimetoprim, florfenikol ve flumequin'e duyarli olduklari ve eritromisin, kanamisin ve ampisiline direncli olduklari belirlendi. Vibrio harveyi ile enfekte olmus baliklarda genellikle solungac filamentlerinde epitel hiperplazisi, ulseratif deri lezyonlari, hepatik hucrelerde, bobrek tubullerinde ve dalagin parankim hucrelerinde dejenerasyon veya nekroz, bobrekte multifokal melanomakrofaj merkezleri ve dalakta hemopoietik dokuda bosalma tespit edildi.

Akim sitometri (AS), 0.2–150 µm buyuklugundeki partikullerin genellikle de hucrelerin tek tek, bir isik demetinin onunden, bir sivi icinde gecerken, anlik olarak olcumlerini yapan daha sonra da coklu fiziksel ozelliklerini analiz eden bir teknolojidir. Akim sitometri, hucre biyolojisini bircok acidan arastirmak ve istenilen hucreleri izole etmek icin kullanilir. Akim sitometri cok sayida tek hucrenin bircok karakteristiklerini hizli bir sekilde olctugunden hucre tabanli analizde altin standart olarak kabul edilmistir. Diger tekniklerle karsilastirildiginda , Akim sitometri’nin hizli veri eldesini ve cok parametreli analizi kolaylastirmasi popularitesinin artmasina ve uygulama alanlarinin genislemesine yol acmistir. Bu derlemede, Akim sitometri’nin su urunleri alanindaki mevcut durumu ve uygulamalari hakkinda ozet bir sekilde bilgi verilmistir.

In this study, moribundsalema (Sarpa salpa) individuals froma public aquarium were investigated to identify the cause of disease. A minorscale loss and partial skin depigmentation were observed in the diseased fish. Internalinvestigation of fish revealed hyperemiain the liver and the intestines and haemorrhages in the muscle tissues. When the histopathological sections oftissues were examined, it was determined that the bacterial infection affected especiallythe gill epithelium, the intestinal mucosa, the heart muscle and hemopoietictissues of the spleen. According to phenotypic and biochemical characteristicsas well as SSU rRNA sequencing results, the isolated bacteria was Vibrio harveyi and consistently seen allthe examined samples of visceral organs including kidney, spleen, liver andblood. However, we need to emphasize that Vibriovulnificus and Pseudoalteromonaspiscicida bacteria were also isolated from blood and spleen tissues of onesick fish among others., Bu çalışma, bir denizakvaryumundan alınan hasta salpa balıklarında (Sarpa salpa) hastalığa neden olan etken veya etkenleri tanımlamaküzere yapılmıştır. Hasta balıkların vücudunda hafif şiddette deri rengindeaçılma ile birlikte pul kayıpları gözlenmiştir. İç bakıda, karaciğer vebağırsak dokularının hiperemik ve kas dokusunun da hemorajik olduğu tespitedilmiştir. Doku kesitleri histopatolojik olarak incelendiğinde, enfeksiyonun;özellikle solungaç epitelyumu, bağırsak mukozası, kalp kası ve dalağın hematopoetikdokusunu etkilediği belirlenmiştir. Fenotipik ve biyokimyasal özellikleri veSSU rRNA dizileme sonuçlarına göre; incelenen tüm iç organlardan (böbrek,dalak, karaciğer) ve kan dokusundan Vibrioharveyi bakterisi izole edilmiştir. Buna ek olarak, incelenen balıklardan sadecebirinin kan dokusundan ve dalağından alınan örneklerde Vibrio vulnificus ve Pseudoalteromonaspiscicida bakterileri de izole edilmiştir.

Bu calismada Liagora ceranoides (Rhodophyta), Halopteris scoparia (Ocrophyta), Padina pavonica (Ocrophyta) ve Sargassum vulgare (Ocrophyta) alglerinin etanol ve metanol ekstraktlarinin hasta gokkusagi alabaligi ( Oncorhynhus mykiss )’ndan izole edilen Yersinia ruckeri suslari uzerine antibakteriyel aktiviteleri degerlendirilmistir. Ayrica, suslarin cesitli antibiyotiklere duyarliliklari da calisilmistir. Baliklardan izole edilen suslar fenotipik testler, API 20E hizli tani kiti ve PZR sonuclarina gore Yersinia ruckeri olarak tanimlanmistir. Calismada L . ceranoides , H . scoparia , P . pavonica ve S . vulgare makroalglerinin metanol ekstraktlarinin Y . ruckeri ’ye karsi antibakteriyel etki gostermedigi bulunmustur. P . pavonica ’nin etanol ekstrakti Y . ruckeri ’ye karsi dusuk antibakteriyel aktivite gostermistir. L . ceranoides , H . scoparia ve S . vulgare makroalglerinin etanol ekstraktlarinin bakteriye karsi antibakteriyel aktivite gostermedigi tespit edilmistir. Antibiyogram test sonuclarina gore suslarin ampisilin, flumekuin, oksitetrasiklin ve trimetoprime duyarli olduklari bulunmustur. Suslar eritromisine karsi orta derecede direnc gostermistir. Sonuc olarak, alglerin antibakteriyel aktiviteye sahip olduklarinin bildirilmesine karsin her alg turunun antibakteriyel aktivite gosteremeyecegi anlasilmistir.

Summary The criteria of testicular maturity during the spawning season and for maturity rates are described according to age for 140 male albacore (Thunnus alalunga, Bonnaterre, 1788) sampled between April and August, 2002–2008 in the Eastern Mediterranean Sea. Histology of gonad samples was used to determine maturity status. Spermatogenesis and its relation to reproductive biology are reported. Fish ranged in fork length (FL) from 63 to 90 cm. The reproductive classes were based upon changes in the testicular morphology and stages of the germinative cells, i.e. immature, developing, maturing, spawning, and spent. Mature stages of testes including the smallest sample of a 63 cm male were observed from May to August of each year during the study. The reported evidence indicates that the size and age of first sexual maturity values of males of the Eastern Mediterranean population are nearly the same as in the Western Mediterranean population, but lower than in the Atlantic stock. The results of this histological investigation, conducted for the first time on this species in the Mediterranean Sea, will enable more precise future estimations for sustainability of the male albacore stock in the Eastern Mediterranean.

Tenacibaculosis, caused by Tenacibaculum maritimum, can result in severe mortalities of several marine fish species and thus represents a major challenge in Mediterranean aquaculture. Serological knowledge about this pathogen is required to develop effective preventive measures (vaccination). For this purpose, nineteen T. maritimum isolates, recovered between 2008 and 2010 from diseased European sea bass (Dicentrarchus labrax, L.) farmed at the Aegean Sea Coasts of Turkey, were characterised. All isolates produced flat, irregular, pale yellow colonies after incubation at 22-24°C for 48 hours, displayed pleomorphism with gliding motility with a size ranging between 4-20 × 0,5 μm and were otherwise biochemically identical to the T. maritimum NCIMB 2154T reference strain. The specific fluorescence appearance of the T. maritimum isolates were revealed by Indirect Fluorescent Antibody Technique (IFAT) which was also used to detect the bacterium in tissue samples. The presence of antibodies in the blood sera of the diseased fish against this pathogen was detected by using agglutination and Enzyme-Linked Immuno Sorbent Assay (ELISA). Dot-Blot testing identified all T. maritimum isolates as serotype O1. To our knowledge, this is the first report on O1 serotype T. maritimum isolates from sea bass farmed in Turkey

Bacteria of the genus Vibrio, which is included in the family Vibrionaceae are commonly found in coastal and estuarine waters. Many Vibrio species can cause diseases in marine fish, crustacean and bivalve species. Moreover, many of them can infect humans after a contact with these animals or consumption of these animals and cause zoonoses. Vibrio harveyi, which was first isolated as a causative agent of a disease problem in a shark species in 1982, was deter-mined to cause diseases and mass mortalities especially in marine invertebrates and in a variety of fish species including aquacultured species such as gilthead sea bream, sea bass and salmo-nid fishes. Deep skin lesions and ulcers, gastroenteric disorders and eye lesions were observed in fish infected with V. harveyi. Primer isolation of this organism can be made on general me-dia such as Tryptic Soy Agar (TSA; supplemented with 2% NaCl) and Thiosulphate-Citrate-Bile salts-Sucrose (TCBS) (semi selective medium for Vibrio species). Besides, Vibrio harveyi Agar (VHA), a media which is developed specially for this species can be used for isolation and species identification. Chloramphenicol, ciprofloxacin and oxytetracycline are recom-mended for the control of disease by various researchers. The aim of this review is to present data to the fish farmers and fish health specialists on the etiology, epizootiology, pathogenicity, clinical symptoms and the pathology, diagnosis, protection and control of Vibrio harveyi and some studies on V. harveyi which is a worldwide distributed bacterium and the causative agent of diseases and mass mortalities in marine animals.

This study was carried out to determine the population of gut flora and investigate the source of the pathogenic bacteria recovered from moribund dentex (Dentex dentex). Transmission electron microscopy (TEM) was used to monitor the translocation of bacterial pathogens which can enter the host through the gut. A total of 260 samples from larvae at different feeding stages were examined, 15 healthy and 50 moribund juvenile dentex were sampled over a 2-year period. Bacterial isolates (n=433) from healthy and moribund fish and their environments were identified by biochemical methods; 75% of them were identified as Gram-negative (mainly Vibrio spp.) and 25% as Gram-positive. Vibrio scophthalmi and other Vibrio species were recovered from moribund fish samples. Some bacteria were recovered from diseased fish reared in hatcheries, introduced mainly from sea water. Among anaerobic bacteria, Eubacterium tarantellae was recovered from larval gut flora while Clostridium botulinum was recovered from juvenile gut flora. TEM also showed that bacterial endocytosis first occurs when fish are fed granulated dry feeds and becomes more prevalent in the juvenile stages when many bacteria are present in the microvilli. TEM also revealed that the bacteria enter the larvae via the mouth and gills before the granulated feeding stage, after which they begin to penetrate the gut and finally also contaminate the marine rearing stage. The results of this study showed that the granulated feeding stage is critical for pathogen invasion in common dentex.