Histological Study of Suprabranchial Chamber Membranes in Anabantoidei and Clariidae Fishes

Morphology of migrating telocytes and their potential role in stem cell differentiation during cartilage development in catfish (Clarias gariepinus)

Telocytes (TCs) are present in a broad range of species and regulate processes including homeostasis, tissue regeneration and immunosurveillance. This novel study describes the morphological features of migrating TCs and their role during cartilage development within the air-breathing organ in Clarias gariepinus, the African sharptooth catfish. Light microscopy (LM), transmission electron microscopy (TEM), and immunohistochemistry (IHC) were used to examine the TCs. TCs had a cell body and telopodes which formed 3D networks in the cartilage canals and extended their telopodes to become the foremost cellular elements penetrating the cartilage matrix. The TCs were also rich in lysosomes that secreted products to the extracellular matrix (ECM). In addition, TCs formed a homocellular synaptic-like structure that had a synaptic cleft, and the presynaptic portion consisted of a slightly expanded terminal of the telopodes which contained intermediate filaments and secretory vesicles. Gap junctions were also identified between TCs, which also connected to mesenchymal stem cells, differentiating chondrogenic cells, macrophages, apoptotic cells, and endothelial cells. In addition to describing the basic morphology of TCs, the current study also investigated migrating TCs. The TC telopodes acquired an irregular contour when migrating rather than exhibiting an extended profile. Migrating TCs additionally had ill-defined cell bodies, condensed chromatin, thickened telopodes, and podoms which were closely attached to the cell body. The TCs also expressed markers for MMP-9, CD117, CD34 and RhoA. In conclusion, TCs may play multiple roles during development and maturation, including promoting angiogenesis, cell migration, and regulating stem cell differentiation. RESEARCH HIGHLIGHTS: Clarias gariepinus telocytes form 3D networks, extend their telopodes and contain lysosomes. Telocytes form a homocellular synaptic-like structure including clefts and a slightly expanded terminal of the telopodes which contains intermediate filaments and secretory vesicles. Gap junctions form between telocytes, which also connect to mesenchymal stem cells, differentiating chondrogenic cells, macrophages, apoptotic cells, and endothelial cells. Migrating telocytes were discovered which had ill-defined cell bodies, condensed chromatin, thickened telopodes exhibiting irregular contours, and podoms which were closely attached to the cell body.

Comparative Morphology of the Digestive Tract of African Bush Fish (Ctenopoma acutirostre) and Paradise Fish (Macropodus opercularis) Inhabiting Asian and African Freshwaters

Anabantidae is a large and diverse group of fish cultured both under aquaculture conditions and as a hobby. These fish share a common structural feature in the form of an additional respiratory organ. Despite the enormous availability of these fish worldwide, little is known about their feeding preferences in husbandry and their influence on homeostasis under both industrial and domestic conditions. This study describes, for the first time, the structure of the digestive tracts of two Anabantoidei fishes: African bush fish (Ctenopoma acutirostre) and paradise fish (Macropodus opercularis). The overall structure of the digestive tract and its histological structure were analyzed and compared in both fish species. Physiological predispositions indicated a predominance of omnivorous fish traits in M. opercularis in contrast to C. acutirostre, which has several morphological traits indicating greater adaptation to carnivory, particularly ichthyophagy. The results obtained will allow further research to be conducted in the future to optimize the nutrition and feeding of these fish and to develop appropriate dietary recommendations.

Association of predation risk with a heterospecific vocalization by an anabantoid fish

Honey gouramis (Trichogaster chuna) received chemical alarm cues derived from conspecific epidermal tissue and, simultaneously, the vocalization produced by a heterospecific gourami species, the sparkling pygmy gourami (Trichopsis pumila). Control trials paired water with the vocalization. In trials that received alarm cues, honey gouramis significantly increased activity relative to control trials that received water, suggesting an attempt to flee and search for refuge. When the recording of the vocalization was later replayed to test fish without any additional chemical cue, fish that had previously experienced the alarm cue froze while those that had received water with the vocalization did not change their behaviour. These data indicate that honey gouramis recognize and respond to chemical alarm cues, making this report the second anabantoid species to be recorded with this response. Second, these data indicate that honey gouramis can associate risk of predation with a novel auditory stimulus, including vocalizations from other species. These data suggest the potential for vocalizations to evolve into alarm signals in this group of fishes.

Experimental Studies on the Impact of the Projected Ocean Acidification on Fish Survival, Health, Growth, and Meat Quality; Black Sea Bream (Acanthopagrus schlegelii), Physiological and Histological Studies

Simple Summary

This study’s data suggest that under the projected scenarios of ocean acidification by 2100 and beyond, significant negative impacts on growth, health, and meat quality are expected, particularly on black sea bream, and will be susceptible to the scientifically approved fish having a weaker resistance to diseases and environmental changes if CO₂ emissions in the atmosphere are not curbed. Knowing the expected consequences, mitigation measures are urgently needed.

Abstract

Acidification (OA), a global threat to the world’s oceans, is projected to significantly grow if CO₂ continues to be emitted into the atmosphere at high levels. This will result in a slight decrease in pH. Since the latter is a logarithmic scale of acidity, the higher acidic seawater is expected to have a tremendous impact on marine living resources in the long-term. An 8-week laboratory experiment was designed to assess the impact of the projected pH in 2100 and beyond on fish survival, health, growth, and fish meat quality. Two projected scenarios were simulated with the control treatment, in triplicates. The control treatment had a pH of 8.10, corresponding to a pCO₂ of 321.37 ± 11.48 µatm. The two projected scenarios, named Predict_A and Predict_B, had pH values of 7.80-pCO₂ = 749.12 ± 27.03 and 7.40-pCO₂ = 321.37 ± 11.48 µatm, respectively. The experiment was preceded by 2 weeks of acclimation. After the acclimation, 20 juvenile black sea breams (Acanthopagrus schlegelii) of 2.72 ± 0.01 g were used per tank. This species has been selected mainly due to its very high resistance to diseases and environmental changes, assuming that a weaker fish resistance will also be susceptibly affected. In all tanks, the fish were fed with the same commercial diet. The seawater’s physicochemical parameters were measured daily. Fish samples were subjected to physiological, histological, and biochemical analyses. Fish growth, feeding efficiency, protein efficiency ratio, and crude protein content were significantly decreased with a lower pH. Scanning electron microscopy revealed multiple atrophies of microvilli throughout the small intestine’s brush border in samples from Predict_A and Predict_B. This significantly reduced nutrient absorption, resulting in significantly lower feed efficiency, lower fish growth, and lower meat quality. As a result of an elevated pCO₂ in seawater, the fish eat more than normal but grow less than normal. Liver observation showed blood congestion, hemorrhage, necrosis, vacuolation of hepatocytes, and an increased number of Kupffer cells, which characterize liver damage. Transmission electron microscopy revealed an elongated and angular shape of the mitochondrion in the liver cell, with an abundance of peroxisomes, symptomatic of metabolic acidosis.