Trunk Kidney Research Articles

A pore-forming protein, perforin, from a non-mammalian organism, Japanese flounder, Paralichthys olivaceus.

A perforin cDNA of Japanese flounder, Paralichthys olivaceus, was cloned from a cDNA library of kidney stimulated with ConA/PMA. The full-length cDNA is 2,157 bp, which encodes 587 amino acids. The Japanese flounder perforin gene consists of five exons and four introns, with a length of approximately 3 kb. The amino acid sequence of the Japanese flounder perforin is 36% identical to that of rat perforin and 37% identical to amino acid sequences of mouse and human perforin. The Japanese flounder perforin also showed low homology to human and mouse complement components (C6, C7, C8 and C9), ranging from 19% to 24%. However, the membrane attack complex/perforin domain is conserved. A phylogenetic analysis placed the Japanese flounder perforin in the same cluster with other known mammalian perforins. RT-PCR analysis revealed that the perforin gene was expressed in the peripheral blood leukocytes, head kidney, trunk kidney, spleen, heart, gill and intestine of healthy fish. Recombinant perforin produced in insect cells using the baculovirus expression system showed calcium-dependent hemolytic activity.

Comparative blood chemistry and histopathology of tilapia infected with Vibrio vulnificus or Streptococcus iniae or exposed to carbon tetrachloride, gentamicin, or copper sulfate

A comparative study was conducted of blood chemistry and histopathology of Nile tilapia ( Oreochromis niloticus) after infection with Vibrio vulnificus or Streptococcus iniae or exposure to carbon tetrachloride (CT), gentamicin (Gm), or copper sulfate (Cu). Treatments were chosen as models targeting different organs and from which different types of lesions were expected. Moderate histological changes were observed in the gill, trunk kidney, liver, spleen, and head kidney in both bacterial infections. Gentamicin induced significant changes in the trunk kidney, liver, and intestine, while carbon tetrachloride treatment caused changes in the liver and trunk kidney. Copper treatment only caused mild proliferation of the gill epithelium. Among the blood chemistry parameters measured, hematocrit, iron, glucose, sodium, and chloride were good indicators of deteriorating health in tilapia, with significant changes in those parameters being observed in most treatment groups. Severity of histopathology in the liver, intestine, and trunk kidney was associated positively with alanine aminotransferase (ALT) and aspartate aminotransferase (AST) but negatively with sodium, chloride, cholesterol, and total protein. Anion gap was the only blood chemistry parameter correlating to histopathology in the spleen and head kidney. Standardized principal component analysis, discriminant analysis, and canonical correlation analysis were applied to the blood chemistry and histopathology data. A consensus set of important parameters that included sodium, chloride, bicarbonate, total protein, ALT, AST, cholesterol, total iron binding capacity, and iron was obtained. Using a 7-parameter model that included potassium, ALT, iron, total protein, bicarbonate, creatine kinase, and AST, 70% of the fish could be correctly classified to the appropriate treatment group, while a 17-parameter model allowed 81% proper classification.

Endocytosis of horse-spleen ferritin in the black tetra, Gymnocorymbus ternetzi (Characidae: Teleostei)

The capability and capacity of various tissues in black tetra Gymnocorymbus ternetzi (Boulenger), family Characidae, to take up horse-spleen ferritin from the blood stream are described. In the head kidney from specimens injected intraperitoneally with horse-spleen ferritin, numerous large cells were tightly packed by yellow-brown granules when the period of time between injection and sacrifice was over 2 h. These cellular granules were tightly packed with Prussian blue precipitation in tissues treated with an acid ferrocyanide solution, i.e., they displayed a deep blue colour. Similarly, smaller cells were also observed in the trunk kidney, gills and peripheral connective tissue of the pancreas and spleen at this stage after ferritin injection, but they were always few in number. Yellow-brown granules or Prussian blue granules were not found in endothelial cell layers of heart and liver. We suggest that practically all clearance of the blood from foreign and scavenger macromolecules is performed by macrophages in the head kidney of the black tetra, whereas the spleen seems to function mainly as a reservoir for red blood cells in this species.

Identification of a novel Japanese flounder (Paralichthys olivaceus) CC chemokine gene and an analysis of its function.

A cDNA of Japanese flounder (Paralichthys olivaceus) CC chemokine designated as Paol-SCYA104 was cloned and sequenced. The cDNA contains an opening reading frame of 315 nucleotides encoding 104 amino acid residues. The full gene was cloned and sequenced from a BAC library. It has a length of approximately 750 bp from the start codon to the stop codon and is composed of four exons and three introns. Four cysteine residues are conserved in the same positions as those of mammalian and fish CC chemokines. Paol-SCYA104 gene was expressed in several organs, including peripheral blood leukocytes (PBLs), head kidney, trunk kidney, and spleen. The recombinant Paol-SCYA104 was expressed in Escherichia coli and the expressed protein was partially purified. The recombinant Paol-SCYA104 was able to attract Japanese flounder PBLs in a microchemotaxis chamber. On the other hand, a negative control, the fraction of the control cells carrying an expression vector lacking the Paol-SCYA104 cDNA, did not show chemotactic activity. These results indicate that Paol-SCYA104 probably acts as a CC chemokine.

A cannulation technique for urine collection from haddock, Melanogrammus aeglefinus L.

Urine collection from fish is an integral part of metabolic studies designed to measure the excretion of various biochemical compounds. The techniques developed for urine collection in salmonids cannot be applied to gadoid fish due to the anatomical differences in their urinary system. The anterior ureter of haddock (Melanogrammus aeglefinus L.) is an elongated duct that originates from the anterior part of the trunk kidney and courses dorsal-posterior to the region of the uropore. The posterior ureter originates from the middle of the caudal kidney, and eventually fuses with the anterior ureter before forming a small urinary bladder. After the two ureters join together, a short common duct empties into the urinary bladder and terminates at the uropore behind the anus. Just before the end, the terminal posterior ureter takes a sharp U-shaped turn, which makes cannulation difficult. We investigated the development of a cannulation technique for urine collection in three different-sized groups of juvenile haddock. In anaesthetized fish, a catheter was inserted in the uropore in a posterior direction to follow the U-shaped course of the ureter. After insertion of the catheter into the uropore, the externalized segment of tubing was connected to a needle attached to a syringe. Urine was then aspirated from each of the 20 fish at 15 μL min−1 for 5 min to measure urine volume and urinary phosphate concentration. The results were reproducible and this cannulation technique has potential for use in other gadoid metabolic studies.

Biochemical and toxicopathic biomarkers assessed in smallmouth bass recovered from a polychlorinated biphenyl-contaminated river

Smallmouth bass (Micropterus dolomieu) were collected to quantify the nature and prevalence of biomarker responses, including biochemical indices, toxicopathic lesions and general health indices, among fish collected from polychlorinated biphenyl (PCB)-contaminated and nearby uncontaminated reaches of the Kalamazoo River, Michigan, USA. Blood and tissue samples (gill, liver, spleen, head kidney, trunk kidney, thyroid and gonads) were collected and preserved at necropsy for biochemical and histological analyses. The body condition factor and liver somatic index were significantly lower in fish collected from the downstream, contaminated site. Plasma vitellogenin was not detected in male fish collected from either site. Liver ethoxyresorufin-O-deethylase activity and liver and spleen superoxide dismutase activity were significantly depressed in fish collected from the downstream site. Significant toxicopathic lesions such as glycogen depletion, enhanced macrophage aggregates, hepatic foci of cellular alteration (i.e. preneoplastic lesions) and neoplasia were also detected in the liver of fish collected from the downstream site. This study indicates that many of the biochemical and histopathological biomarker responses were associated with liver and body tissue PCB concentrations. Taken together, the biomarkers of exposure and effect strongly suggest that fish within the downstream site are adversely affected by PCBs and other chemical stressors.

Response of Channel Catfish to Diets Containing T-2 Toxin

The T-2 toxin is a trichothecene mycotoxin produced by certain molds of the genus Fusarium that infect the grains, wheat by-products, and oilseed meals used in the production of animal feeds. An aquarium study was conducted with juvenile channel catfish Ictalurus punctatus. Experimental diets were prepared by replacing the untreated casein in a semipurified diet with casein treated with pure T-2 toxin in the amounts necessary to produce five levels of the toxin. Dietary concentrations were 0, 0.625, 1.25, 2.5, and 5.0 mg/kg of diet. A concurrent study with similarly sized channel catfish was conducted to substantiate the toxicity of the T-2 toxin. This study required feeding the control diet at the same levels of daily consumption (pair-feeding) as in the treatments with the three highest levels of T-2 toxin (1.25, 2.5, and 5.0 mg/kg) to compare differences in weight gain, feed conversion, hematocrit, and survivability. After 8 weeks, significant (P < 0.05) reductions in growth were observed for all treatments fed T-2 toxin compared with the control diet. Significantly poorer feed conversion was found only for the highest level of T-2 toxin. Hematocrit values were adversely affected by the inclusion of T-2 toxin at 1.25, 2.5, and 5.0 mg/kg. Pair-fed catfish had a significantly greater increase in body weight than fish fed the highest level of mycotoxin only. Pair-fed treatments had hematocrit values that were very similar to those of the control and significantly higher than those of fish receiving 1.25, 2.5, and 5.0 mg/ kg. The survivability of the fish fed T-2 toxin at 2.5 and 5.0 mg/kg was significantly lower than that of control fish and their pair-fed counterparts. Histopathological anomalies of stomach, head, and trunk kidneys were observed in fish receiving the three highest levels of T-2 toxin. These results demonstrate that this feed-borne mycotoxin is toxic to juvenile channel catfish.

Comparative challenge model of Flavobacterium columnare using abraded and unabraded channel catfish, Ictalurus punctatus (Rafinesque).

The early entry of the fish pathogen Flavobacterium columnare and enhancement by abrasion was studied in channel catfish, Ictalurus punctatus (Rafinesque), using the polymerase chain reaction and a species-specific primer set for a bacterial 16S rRNA gene product. Evaluations were conducted following an abrasion bath immersion challenge with F. columnare. Abrasion, a practice which has historically been used prior to bacterial challenge, had significant effects on the early entry of the pathogen and on cumulative percent survival (CPS). The FvpF1-FvpR1 primer set was useful in detecting the early entry of F. columnare in mucus, skin, gill, blood, liver and trunk kidney tissues in both abraded and unabraded fish following immersion challenge at 29 +/- 2 degrees C. Bacteria were detected earlier in all tissues in abraded fish, except in the trunk kidney. These differences were not significant, except in the case of blood. Mucus, skin and gill tissues were positive for F. columnare earliest regardless of treatment (after 5 min in abraded fish and after 15 min in unabraded fish). CPS following challenge with F. columnare was significantly affected by abrasion, which supports the use of abrasion for the F. columnare challenge model for channel catfish.

Cloning and characterisation of a cDNA encoding Japanese flounder Paralichthys olivaceus IgD

A cDNA containing the gene for Japanese flounder IgD consisted of 3240 bp encoding 998 amino acid residues. The amino acid sequence of the constant region of Japanese flounder IgD shares 38–80% identity with the sequences of previously reported teleost IgDs. The structure of the constant region of Japanese flounder IgD, which contains the μ1, δ1, δ2, δ3, δ4, δ5, δ6, δ7, and TM regions, is similar to the structures of the constant regions of the IgDs of channel catfish and Atlantic salmon. Southern blot hybridisation showed that the Japanese flounder IgD gene exists as a single locus. The Japanese flounder IgD gene was mainly detected in peripheral blood leucocytes (PBLs) and small amounts were detected in the spleen, head and trunk kidney, although IgM mRNA was detected in similar amounts in PBLs, the head kidney, and spleen. The copy number of IgM mRNA in Japanese flounder PBL was 56-fold higher than that of IgD.

Histological studies on the lymphoid organs in prenatal larvae of platy, Xiphophorus maculatus L. (Poeciliidae: Teleostei)

The thymus was very large and tightly packed by lymphocytes in prenatal larvae of platy, Xiphophorus maculatus L., whereas the lymphoid tissues in the spleen and trunk kidney were poorly developed at these stages. We therefore suggest that the specific cellular defence is developed much earlier than the corresponding humoral defence mechanisms in this species.

Streptococcus iniae infection and tissue distribution in hybrid striped bass (Morone chrysops×Morone saxatilis) following inoculation of the gills

This study was designed to test the possibility that Streptococcus iniae enters through the gills and causes infection in hybrid striped bass. To determine the dose response, four groups of fish were inoculated with S. iniae via the gills with a dose of 5.010 5 , 2.610 6 , 5.010 6 , or 1.010 8 CFU/fish. One group of fish was inoculated with tryptic soy broth (TSB) via the gills to serve as controls. The cumulative percent mortality was 13%, 27%, 100% and 100% for 5.010 5 , 2.610 6 , 5.010 6 and 1.010 8 CFU/fish, respectively. We also examined the tissue dissemination of S. iniae at 0.5, 4, 8, 12, 24, 48 and 72 h after experimental gill inoculation. Fish were inoculated with 2.610 6 or 5.010 6 CFU/fish, which caused low and high mortality, respectively. Within 48 h, fish inoculated with the 2.610 6 dose were culture positive on the gill surface, blood of the first and second gill arches, blood of the third and fourth gill arches and the nares. However, for the dose of 5.010 6 CFU/fish, S. iniae was also isolated from the olfactory, optic and cerebellum regions of the brain, eye, head kidney, trunk kidney, spleen and liver at 48 h. For the 2.610 6 dose, S. iniae was not isolated until 48 h post-inoculation, but was isolated at 12 h for the 5.010 6 dose. The results of this study indicate that S. iniae can enter hybrid striped bass through the gills. However, mortality at similar S. iniae doses was lower than we previously observed by inoculation of the nares. D 2003 Elsevier Science B.V. All rights reserved.

Experimental oral transmission of largemouth bass virus

AbstractLargemouth bass virus (LMBV) is a recently discovered iridovirus that causes a fatal disease of largemouth bass, Micropterus salmoides (Lacepède). Fish can become infected by waterborne LMBV, but oral transmission of this virus has not been demonstrated previously. Largemouth bass were gavaged with guppies, Poecilia reticulata Peters, which had been injected with LMBV, and then sampled periodically during a 7‐week observation period. The dose of LMBV averaged 105.6 tissue culture infectious doses – 50% cytopathic endpoint (TCID50) per largemouth bass. Five of 24 largemouth bass exposed to LMBV became infected with the virus, but none of the fish had clinical signs typical of LMBV disease. Virus titres in largemouth bass were highest in swim bladder (105.5–9.5 TCID50 g−1) and were 105.2 TCID50 g−1 or lower in cutaneous mucus, head kidney, trunk kidney, spleen, gonad and intestine. These results indicate that LMBV can be transmitted orally to largemouth bass, but further study is needed to determine the factors affecting pathogenicity of the virus.

Immunolocalization of cysteine proteinases (cathepsins) and cysteine proteinase inhibitors (salarin and salmon kininogen) in Atlantic salmon, Salmo salar.

Tissue localization of cysteine proteinases (cathepsins) and their inhibitors (salarin, salmon kininogen) was performed in tissues of the Atlantic salmon. In skin, both epidermis and dermis were strongly stained by antisera against salarin and salmon kininogen. In epidermis the intercellular space seemed to be heavily stained (salarin). In kidney, the inhibitors were mainly localized to the interstitial capillaries. Also, some epithelial cells of the tubules (salarin) and some cells of the interstitium were stained. Mostly, the staining had a diffuse cytoplasmic localization. In the liver some hepatocytes were strongly positive for salarin and salmon kininogen. Purified fish cysteine proteinase inhibitors were not found to inhibit the growth of fish pathogenic bacteria and viruses. In the trunk kidney cathepsins B and L were localized in epithelial cells of the tubules (proximal part) and in cells of the interstitium. Mostly, the staining showed a prominent lysosomal localization. In head kidney large macrophage-like cells were positively stained for cathepsin B. The staining was localized to granula/vacuoles in the cytoplasm. In the liver, some hepatocytes were strongly stained and some were less strongly positive for cathepsin B and L. Mostly, the hepatocytes showed lysosomal staining. Cathepsin L was found in some big macrophage-like cells in the spleen. Mucosal epithelial cells of the esophagus and intestine seemed to be strongly stained for cathepsin B and L. The results show that cathepsins and their inhibitors are specifically and widely distributed in the Atlantic salmon skin indicating that they perform some biologically important and specific but so far unknown functions.

Tissue-specific expression of AHR2, ARNT2, and CYP1A in zebrafish embryos and larvae: effects of developmental stage and 2,3,7,8-tetrachlorodibenzo-p-dioxin exposure.

To better understand the role of the aryl hydrocarbon receptor (AHR) signaling pathway in causing tissue-specific signs of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) toxicity in zebrafish, the temporal and spatial expression of the zebrafish aryl hydrocarbon receptor 2 (zfAHR2), aryl hydrocarbon receptor nuclear translocator 2 (zfARNT2), and an AHR regulated gene, cytochrome P4501A (zfCYP1A), were assessed in larvae exposed to vehicle or TCDD (1.55 nM) from 3-4 h postfertilization (hpf). Coexpression of a transcriptionally active AHR pathway was apparent by the expression of zfCYP1A mRNA and protein in certain larval tissues. zfCYP1A protein was first detected in the skin and vasculature of TCDD-exposed larvae at 36 hpf. Vascular-specific zfCYP1A protein expression continued from 36 to120 hpf at which time it was also detected in the heart, kidney, and liver. zfCYP1A mRNA was observed in TCDD treated larvae as early as 24 hpf in the developing vascular system. Vascular specific zfCYP1A mRNA expression in the head, trunk, and tail by 36 hpf in TCDD-exposed larvae, confirmed immunohistochemical localization. The expression of zfAHR2 and zfARNT2 mRNAs was generally similar in control and TCDD-exposed larvae. Coexpression of zfAHR2, zfARNT2, and zfCYP1A mRNAs was evident in TCDD-exposed larvae by 36 hpf and in the vasculature, heart, and trunk kidney by 48 hpf, well before the first signs of overt developmental toxicity are observed. In addition to their function in response to AHR agonists, zfAHR2 and zfARNT2 may be involved in development and function of the nervous system. zfAHR2 and zfARNT2 were detected in the brain, spinal cord, and sensory organs. However, TCDD-induced zfCYP1A expression was not detected in these tissues. Taken together, these results are consistent with the notion that the cardiovascular system is a primary target of TCDD developmental toxicity in zebrafish.

Edwardsiella ictaluri bacteraemia elicits shedding of Aeromonas hydrophila complex in latently infected channel catfish, Ictalurus punctatus (Rafinesque)

Edwardsiella ictaluri is a primary bacterial pathogen of channel catfish, Ictalurus punctatus, and the causative agent of enteric septicaemia of catfish. Edwardsiella ictaluri is known to gain entry to the host by infection of the nares, gastrointestinal tract, and gills, and to disseminate to organs via an as yet uncharacterized acute bacteraemia. In this study, fluorescent microscopy showed E. ictaluri on the gill within 5 min of immersion challenge and E. ictaluri could also be isolated from the circulation within 5 min. When removed to clean water, catfish cleared circulating bacteria within 15 min and the blood remained free of E. ictaluri until its reappearance at the 12 h post‐infection sampling. However, Aeromonas hydrophila, the aetiological agent of motile aeromonad septicaemia, appeared within the circulation 7 h post‐challenge with E. ictaluri and was detected in all fish at 12 h post‐infection. Only 20% of fish carried A. hydrophila in the trunk kidney that could be detected by plate culture on Rimler–Shotts agar; however, 100% of challenged and stress‐control fish were A. hydrophila complex positive at 24 h post‐challenge. These results suggest that although the catfish is capable of clearing its circulation of E. ictaluri, superinfection with latent A. hydrophila may enhance clinical signs of edwardsiellosis. This is the first report of a bacterial superinfection appearing in fish.

Histological and Hematological Evaluation of Potassium Permanganate Exposure in Channel Catfish

Abstract A histological and hematological study was performed to evaluate the effect of waterborne exposures of channel catfish Ictalurus punctatus to potassium permanganate (KMnO4). Three concentrations of KMnO4 were chosen to represent one, three, and five times the therapeutic concentrations (0.438, 1.315, and 2.190 mg/L, respectively), based on the KMnO4 demand, for 36 h, which is three times the usual treatment duration. The organs examined were the gill, liver, and trunk kidney. Differential leukocyte counts of neutrophils and monocytes in the blood and plasma enzyme analyses (lactate dehydrogenase and alanine transaminase) were also performed. The gill was the only organ to show microscopic lesions. Fish exposed to the therapeutic concentration of KMnO4 for 36 h had mild hypertrophy and spongiosis in the gills sampled during exposure, but no lesions were noticed 2 d postexposure. Gills of fish exposed to three and five times the therapeutic dose had extensive hyperplasia, epithelial hypertrophy and...

Identification of mRNA and protein expression of the Na/K-ATPase α1-, α2- and α3-subunit isoforms in Antarctic and New Zealand nototheniid fishes

Antarctic nototheniids living in waters below 0 °C have a serum osmolality nearly double that of temperate nototheniids. Warm acclimation of Antarctic nototheniids to +4 °C decreases serum osmolality by 25% and nearly doubles gill Na/K-ATPase activity without an increase in Na/K-ATPase number or a change in the enzyme's affinity for ouabain. However, the increased activity may result from a change in gill Na/K-ATPase α-subunit isoform composition. Four known Na/K-ATPase α-subunit isoforms have been identified in other species, however, identification of the isoforms in teleosts has been incomplete. Using reverse transcriptase-polymerase chain reaction (RT-PCR) and cloning, we have identified partial cDNA sequences of the Na/K-ATPase α1-, α2- and α3-subunit isoforms in the Antarctic nototheniid Trematomus bernacchii. Using isoform-specific primers, the mRNA for all three isoforms was found in T. bernacchii brain, gill, heart, trunk kidney and muscle. Using isoform-specific antibodies, the Na/K-ATPase α1-, α2- and α3-subunit isoforms were found in the tissues of both T. bernacchii and Notothenia angustata, a temperate nototheniid. This is the first report detecting all three isoforms at the nucleotide and protein level in teleosts. Further experiments will determine if the gill T. bernacchii Na/K-ATPase α-subunit isoform composition changes during warm acclimation.

Composition of main haematopoietic compartments in normal and bled channel catfish

Differential cell counts showed that the head and trunk kidney of control and bled channel catfish Ictalurus punctatus had myeloid characteristics. They contained lymphoid and granuloid cells, thrombocytes, erythroid and agranular cells in decreasing order of abundance (%). Among the blast and precursor cells, the most numerous erythroid ones were followed by granuloid, lymphoid and agranular ones. The main changes after blood withdrawal were the decrease of thrombocytes and the increase of precursor cells in both kidney parts. In the group examined 7 days after bleeding the head kidney had a higher percentage of erythroid cells and lymphocyte precursors than the trunk kidney while the latter had more granuloid cells and their precursors. Basophils were present (c. 1%) in both regions of the kidney of all groups. The spleen was predominantly a lymphatic organ. It contained c. 80% lymphoid cells, a higher incidence of granulated lymphocytes than in kidneys, 15% thrombocytes and 1.4% agranular cells. Blood withdrawal caused an increase of thrombocytes, a decrease of lymphoid cells and an increase of erythroid precursors in the spleen. The last probably stemmed from the circulation. While haematocrit values failed to indicate the anaemic state in the bled groups, the differential red blood cell count showed dramatic differences between the control and bled groups as well as between the two groups in different stages of recuperation from the blood loss.

Composition of main haematopoietic compartments in normal and bled channel catfish

Differential cell counts showed that the head and trunk kidney of control and bled channel catfish Ictalurus punctatus had myeloid characteristics. They contained lymphoid and granuloid cells, thrombocytes, erythroid and agranular cells in decreasing order of abundance (%). Among the blast and precursor cells, the most numerous erythroid ones were followed by granuloid, lymphoid and agranular ones. The main changes after blood withdrawal were the decrease of thrombocytes and the increase of precursor cells in both kidney parts. In the group examined 7 days after bleeding the head kidney had a higher percentage of erythroid cells and lymphocyte precursors than the trunk kidney while the latter had more granuloid cells and their precursors. Basophils were present (c. 1%) in both regions of the kidney of all groups. The spleen was predominantly a lymphatic organ. It contained c. 80% lymphoid cells, a higher incidence of granulated lymphocytes than in kidneys, 15% thrombocytes and 1.4% agranular cells. Blood withdrawal caused an increase of thrombocytes, a decrease of lymphoid cells and an increase of erythroid precursors in the spleen. The last probably stemmed from the circulation. While haematocrit values failed to indicate the anaemic state in the bled groups, the differential red blood cell count showed dramatic differences between the control and bled groups as well as between the two groups in different stages of recuperation from the blood loss.

Morphogenesis of blood cell lineages in channel catfish

The morphogenesis of blood cell lineages in channel catfish Ictalurus punctatus, from head and trunk kidney and spleen imprints as well as from blood smears of bled and control fish, showed that early maturation stages resembled those in higher vertebrates. The erythroid lineage consisted of the proerythroblast, erythroblasts (basophilic, polychromatic, orthochromic), young erythrocyte and erythrocyte. The rare bilobed erythrocyte seemed to be a cell in apoptosis while old erythrocytes and erythroplastids represented remnants of this process. Maturation stages of neutrophils and basophils encompassed the granuloblast, young progranulocyte, progranulocyte and metagranulocyte. The basophilic lineage was regularly present in kidneys, rare in spleen and absent from blood. It contained large Sudan Black and PAS‐negative, water soluble granules and small PAS‐positive ones. Lymphocytes with azurophilic granulation occured regularly in kidneys and spleen. Monoblasts and promonocytes in kidneys preceded monocytes. A phagocytic lineage devouring apoptotic blood cell remnants was present in kidneys and spleen. Its youngest identified stage (promacrophage) resembled more a granuloid cell without granules than a monocytoid one. The larger, young macrophages contained a few to several ingestions and the very large mature macrophages were loaded with them. The latter two stages corresponded to cells in melano‐macrophage centres (macrophage aggregates). Precursor stages of the thrombocyte were not identified.