The development of digestive tract and accessory glands in Hamun mahi (Schizothorax zarudnyi, Family: Cyprinidae) from hatching to 21 days after hatching (DAH) is described in this study. This information is critical for evaluating the digestive tract functional capacity and physiology of digestion in larvae, and designing optimal rearing techniques and artificial diets for this commercially valuable species. Based upon its feeding mode and structural changes in the digestive tract, larval ontogeny in S. zarudnyi was divided into three stages, Stage 1: 0-2 DAH, Stage 2: 3-8 DAH and Stage 3: from 9 DAH onwards. As in most teleosts, Hamun mahi at hatching had an undifferentiated digestive tract. The most critical ontogenetic events occurred at Stage 2. At the beginning of Stage 2, mouth opened in conjunction with the differentiation of the digestive tract. During Stages 2 and 3 the gut differentiated, and buccopharyngeal cavity, oesophgus and incipient intestine became distinguishable. At this stage digestive tract processes continued to develop (e.g. entrocyte's brushborders, appearance of digestive mucous cells at 4 DAH, and gut mucosal folds). The first taste buds and pharyngeal teeth appeared at the beginning of Stage 2. Histological observations suggest that digestive tract development of the Hamun mahi larvae, involving the presence of functional liver (vacuolated hepatocyes), exocrine and endocrine pancreas, and gallbladder enabled early larvae (from 3 DAH) to ingest, digest and assimilate the first exogenous food, even before endogenous reserves were completely resorbed. From Stage 3 onwards, most organs essentially exhibited an increase in tissue structure, size and number.
The present study describes histological aspects of the development of gills, heart, kidney, swim bladder and spleen from Day 0 up to Day 21 after hatching in Hamun mahi Schizothorax zarudnyi larvae and provides valuable information on its structural status during ontogeny. This information is particularly useful for establishing the functional systemic capabilities and physiological requirements of larvae for optimal welfare and growth. Observations described are related to main developmental stages of Hamun mahi and are defined on the basis of external morphological features. Pronephric excretory structures, a tubular heart and respiratory anlage are present at hatching but spleen and swim bladder become apparent during Stage 2. During the first two stages, Hamun mahi larvae undergo intense organogenesis particularly during Stage 2. Despite Stage 2, the next developmental stage is not characterized by the appearance of new structures but by the increase in size and complexity of the preexisting ones.Bu çalışma, hamun mahi (Schizothorax zarudnyi) larvalarında yumurtadan çıktıktan sonra 0. günden 21. güne kadar geçen sürede solungaç, kalp, böbrek, yüzme kesesi ve dalak gelişiminin histolojik özelliklerini tanımlamaktadır ve türün ontogenez sırasındaki yapısal durumu hakkında değerli bilgiler sağlamaktadır. Bu bilgiler özellikle larvaların yapısal sistemik kabiliyetlerinin ve en uygun refah koşulları ile gelişimi için gerekli fizyolojik ihtiyaçlarının belirlenmesinde fayda sağlamaktadır. Bahsedilen bulgular hamun mahi balığının temel gelişim basamakları ile ilişkilidir ve dış morfolojik özelliklerine göre tespit edilmiştir. Pronefrik salgı yapıları, tübüler bir kalp ve solunum sistemi taslağı yumurtadan çıkışta bulunmaktadır fakat dalak ile yüzme kesesi 2. safhada belirgin hale gelmektedir. Hamun mahi larvaları ilk iki safha boyunca, özellikle de 2. safhada yoğun bir organogenezis geçirmektedir. 2. safha, daha ileri bir gelişimsel safha olmasına rağmen yeni yapıların görülmesiyle karakterize edilmemekle birlikte, daha önceden var olan organların boyca büyümesi ve daha karmaşık bir hal almasıyla tanımlanmaktadır.
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