Effect of dendritic organ ligation on striped eel catfish Plotosus lineatus osmoregulation.

Unique amongst the teleost, Plotosidae catfish possess a dendritic organ (DO) as a purported salt secreting organ, whereas other marine teleosts rely on their gill ionocytes for active NaCl excretion. To address the role of the DO in ionregulation, ligation experiments were conducted in brackish water (BW) 3‰ and seawater (SW) 34‰ acclimated Plotosus lineatus and compared to sham operated fish. Ligation in SW resulted in an osmoregulatory impairment in blood (elevated ions and hematocrit) and muscle (dehydration). However, SW ligation did not elicit compensatory changes in gill or kidney Na+/K+-ATPase (NKA) activity and/or protein expression while a decrease in anterior intestine and increased in posterior intestine were observed but this was not reflected at the protein level. Following ligation in SW, protein levels of carbonic anhydrase (CA) and V-ATPase B subunit (VHAB) were higher in kidney but either lower (CA) or unchanged (VHAB) in other tissues. Taken together, the osmotic disturbance in ligated SW fish indicates the central role of the DO in salt secretion and the absence of a compensatory response from the gill.

Early sexing techniques in Lophiosilurus alexandri (Steindachner, 1876), a freshwater carnivorous catfish.

This study aimed to evaluate sexing techniques for juvenile Lophiosilurus alexandri. With this aim, we evaluated three techniques: coelioscopy, performed with the use of video surgery equipment; coeliotomy, a surgical procedure for direct visualization of the gonads; and sex determination using a urethral probe to compare the genital papillae. For coelioscopy, the survival rate was 100% 30 days after the procedure, and the fish restarted eating 10 days after surgery. This technique resulted in a 100% correct identification of individuals identified as females, whereas for males, it was 66.6%. There was no significant difference between males and females for anesthesia induction and recovery times. However, the procedure took longer for males because of the difficulty in observing the gonads, which can be attributed to the large amount of visceral fat in males. Coeliotomy also resulted in a 100% survival rate 30 days after surgery, and the efficiency of this technique was 96.3% for males and 93.9% for females. The fish restarted eating between 10 and 14 days after surgery, and there were no significant differences between males and females for anesthesia induction and recovery times for the surgical procedure to visualize the gonads (P > 0.05). The urethral probe technique was less efficient with an accuracy rate of 67.8% and 81.8% for males and females, respectively. We conclude that coeliotomy was more efficient for sexing both sexes of juvenile L. alexandri.

Reproductive performance of partial gonadectomized male African catfish, Clarias gariepinus broodstocks.

This study was conducted to evaluate the effect of partial gonadectomy on reproductive performance of male Clarias gariepinus broodstock. Testes from C. gariepinus broodstock were surgically removed; 25% of the testes (Treatment 1), 50% of the testes (Treatment 2), 75% of the testes (Treatment 3), and removal of the sperm from the testes sac using syringe after the abdominal cavity had been cut open (Treatment 4) {control}. The incisions were sutured and the fish kept inside separate concrete tanks for 4 mo. The incisions closed up within 8 to 9 wk of surgery. The postsurgical survival of C. gariepinus was 100%, indicating the efficiency of the surgical procedure. There was no significant difference (P > 0.05) in sperm production, percentage fertilization, hatchability and survival of the larvae using sperm derived from regenerated testes of the partially gonadectomized C. gariepinus and nongonadectomized C. gariepinus. It also reveals that partial gonadectomy could not alter the quality of sperm production of C. gariepinus. Sperm derived from regenerated testes performed effectively for fertilization of eggs. Based on the results of this study, the removal of 75% of testes during partial gonadectomy proved to be the best as the total number of spermatozoa was more than that of other methods and the sperm was able to fertilize more eggs. Hence the removal of 75% of testis during partial gonadectomy of C. gariepinus is recommended based on the results of this study.

Comparison of two methods of attaching telemetry transmitters to the Mekong giant catfish, Pangasianodon gigas.

For conservation and successful stock enhancement of endangered species, an understanding of the movement patterns and behavior of the target species is indispensable. The Mekong giant catfish, Pangasianodon gigas, is endemic to the Mekong Basin and now is threatened with extinction. Although biotelemetry using acoustic transmitters and receivers is expected to reveal its movement patterns and behavior, the most suitable attachment method for the transmitter to the catfish is unknown. In this study we examined the effects of external attachment and surgical implantation on the survival and growth of the catfish, compared with those in control individuals, in an earthen fish pond for approximately 2 months. No fish died during the experimental period. Furthermore, we found no fungal infections in any fish and no significant differences in growth rate among treatment and control fish. However, all transmitters of externally tagged fish were lost during the experimental period. In contrast, transmitters of some surgically implanted fish remained in the peritoneal cavity. In conclusion, the surgical implantation technique is suitable for long-term monitoring of the catfish.

Surgical removal of stones in the stomach of a tiger shovelnose catfish.

A seven months old, tiger shovelnose catfish was referred to the veterinary medical teaching hospital of the college of veterinary medicine, Konkuk university because of suspecting a foreign body in the stomach. By physical and radiologic examinations, the catfish revealed abdominal enlargement, vomiting, inactivity and radiopaque foreign bodies in the stomach. Under general anesthesia with dilute isoflurane solution, celiotomy was performed. Stomach was atonic, and three foreign bodies were palpated in the stomach. In this process, three stones came out through mouth. Abdominal muscles were closed with a simple continuous suture pattern, and skin was closed with a simple mattress suture pattern. Sutured site was covered with glue and mucous taken from allogenic skin. On the second day after surgery, the patient recovered to normal condition, showing increased appetite and activity.

Surgical removal of stones in the stomach of a tiger shovelnose catfish

A seven months old, tiger shovelnose catfish was referred to the veterinary medical teaching hospital of the college of veterinary medicine, Konkuk university because of suspecting a foreign body in the stomach. By physical and radiologic examinations, the catfish revealed abdominal enlargement, vomiting, inactivity and radiopaque foreign bodies in the stomach. Under general anesthesia with dilute isoflurane solution, celiotomy was performed. Stomach was atonic, and three foreign bodies were palpated in the stomach. In this process, three stones came out through mouth. Abdominal muscles were closed with a simple continuous suture pattern, and skin was closed with a simple mattress suture pattern. Sutured site was covered with glue and mucous taken from allogenic skin. On the second day after surgery, the patient recovered to normal condition, showing increased appetite and activity.