Clarias

The chapter summarizes current knowledge on fish biology in Lake Kinneret. Nineteen native fish species belonging to six families populate the lake. Three of these species are endemic to the lake and four other species are endemic to the Jordan Valley system. Eight alien species are found in the lake. Four of them are breeding in nature, three can’t breed but are regularly stocked, and one is a hitchhiker that can’t breed. Growth rate equations and weight-length relationships are presented for the dominant cyprinids (Mirogrex terraesanctae, Hypophthalmichthys molitrix, Cyprinus carpio, Barbus longiceps, Capoeta damascina, Carasobarbus canis), cichlids (Oreochromis aureus, Sarotherodon galilaeus, Tilapia zillii, Tristramella simonis), grey mullets (Liza ramada, Mugil cephalus), and catfish (Clarias gariepinus).    The long-term changes in fish community composition in the lake were associated with introduction and invasion of fishes; changes in fishing intensity; modifications of the littoral, and changes of the lake ecological regime. Temporal dynamics, spatial distribution, total abundance and biomass of fish in the lake were studied based on long-term hydroacoustic monitoring. The size structure and abundance of fish in the pelagic zone of the lake display explicit seasonal changes associated with fish spawning migrations and winter-spring recruitment of the dominant bleak M. terraesanctae. Water level fluctuations beyond natural have modified the littoral habitats, which are of specific importance during different life stages of fish. Water level has an immense impact on fish reproduction, survival, recruitment, population dynamics, and eventually determines the catches of commercially important species.
See also chapter: "Fisheries Management"

In fish farming, feeding rate is an important factor affecting the growth of fish, and thus determining the optimal feeding rate is important to the success of any aquaculture operation. This study which lasted for 99 days investigated the effect of varying feeding rates on the growth response of African catfish, Clarias gariepinus fingerlings. One hundred and eighty fingerlings were randomly distributed into nine experimental tanks giving 20 fingerlings per tank with an initial weight of 5.92±0.006 g. Three feeding rates were employed as treatments – 3%, 5%, and 7% of fresh body weight, with three replicates per treatment. The fishes were fed three times daily with commercial feed (Aller-aqua) of 42% crude protein. Growth and water quality parameters were measured fortnightly and feed ration adjusted according to the biomass in each tank. Results show that Final Mean Weight, Mean Weight Gain, Specific Growth Rate, Performance Index and Protein Efficiency Ratio were significantly hi...

The impact of Endosulfan, an organochlorine pesticide on the gills of Indian freshwater catfish, Clarias batrachus was evaluated. The experimental group was exposed to 0.5μg/L of endosulfan for 30 days. Experimental and control fishes were sacrificed every 10 days for 30 days. The gills were fixed in Bouin's solution, dehydrated in graded ethanol, infiltrated in xylene, sectioned at 4-6μm and stained in hematoxylin and eosin. Epithelial necrosis, hypertrophy of epithelial cells, rupture of gill epithelium and hemorrhage at primary lamellae were observed in fishes after 10 days of exposure, while lifting of the epithelium, oedema and fusion of adjacent secondary lamellae were conspicuous in fishes of 20 days of exposure. No effects were however observed in control fishes. The authors believe that endosulfan is significantly toxic to the fish, so much so that it may lead to asphyxia and subsequent killing of the fish.

The present study was carried out to screen autochthonous gut bacteria in freshwater air breathing walking catfish, Clarias batrachus Linnaeus. Altogether, 100 extracellular enzyme-producing bacteria were isolated from the foregut (FG) and hindgut (HG) regions. Data were presented as log viable counts g-1 gut (LVC). The occurrence of heterotrophic bacterial population was higher in the FG region (LVC = 8.25) than the HG (LVC= 7.3). Similarly, proteolytic, amylolytic and lipolytic bacteria in FG outnumbered (LVC=7.25, 6.77 and 5.23 respectively) the HG (LVC=6.38, 5.58 and 4.04 respectively). However, occurrence of cellulolytic bacteria in both, FG and HG was less (LVC=2.1 and 1.34 respectively) in comparison to the other extracellular enzyme-producing bacteria. Out of the 100 bacterial isolates, 22 isolates were primarily selected through qualitative assay of extracellular enzyme activities. Among them, 3 promising isolates were chosen as potent extracellular enzyme producers on the ...