Studies on the larval development of fish are essential for conservation and improvements in cultivation techniques. Geophagus brasiliensis popularly known as Cará has potential as a fish of interest in ornamental aquaculture. Wild adults of G. brasiliensis were kept in an aquarium for spontaneous reproduction. Newly hatched larvae were transferred to 5-litre aquaria at 22, 26 and 30°C until total yolk sac resorption. Histological slides were used for biometric analysis and monitoring of larval ontogenesis at different temperatures. Histologically, from the first to the fourth days it was possible to identify myomeres, optic vesicle, yolk syncytial layer, brain, heart and differentiation of the eye layers. From the fourth to the seventh days, it was possible to identify mandibular and gill cartilages, swim bladder, liver, prismatic epithelium with striated border in intestine and renal epithelium. All biometric measurements increased over the days, except height and length of the yolk sac, which gradually decreased until the complete resorption of the yolk sac that occurred on the fifth day at a temperature of 30°C, the sixth day at 26°C and the seventh day at 22°C. Morphological events at 30°C such as the reabsorption of the yolk sac, the appearance of cartilage in the branchial arches and differentiation of the layers of the eyes occurred faster compared with the other temperatures tested. Opening of the mouth and digestive tract occurred at a similar time on the fourth day in all temperatures.

The present study evaluated the effects of low salinity on the early larval development of Oreochromis niloticus, specifically histological damage to white muscle, morphology of the yolk-sac surface and trunk area, and molecular expression of apoptosis and cell proliferation biomarkers. Newly hatched larvae were submitted to four salinity treatments for a period of 48 or 72 h, in duplicate: (S0) freshwater, (S2) 2 g l−1, (S4) 4 g l−1, and (S6) 6 g l−1NaCl. Larval development was examined using histology, electron microscopy, enzyme-linked immunosorbent assay (ELISA), and morphometry. At the yolk-sac surface, larvae of S4 and S6 displayed alterations to the apical opening of chloride cells that may be related to osmotic expenditure caused by the increased salinity. Caspase-3 expression did not differ significantly among treatments, however significantly lower proliferating cell nuclear antigen (PCNA) expression (P < 0.05) suggested minor cell proliferation in larvae of S4 and S6 compared with S0 and S2. Furthermore, there was a significant reduction in both trunk area and percentage of normal white muscle fibres (WF) in larvae of S4 and S6. Vacuolated areas and myofibrils concentrated at the cell periphery and found in the white muscle from larvae exposed to saline environments suggested disturbance to muscle development. Oedema and mononuclear infiltrate were also observed in the white muscle of S4 and S6 larvae. Together these results indicated that treatments with 4 and 6 g l−1 NaCl may cause osmoregulation expenditure, morphological alterations to the yolk-sac surface and histological damage to skeletal muscle that negatively affected the early larval development of O. niloticus.

The impact of practically all the everyday stress factors occurring in the first days of the chick life on the rate of the utilisation of the yolk sac content, on the chicken immune status and on the growth of the animal's body and intestinal masses was investigated. The impact of the stress was investigated during the first five days of chick's life. The chicks were divided into five groups, each comprising 44 birds. The first chick group was exposed to moderate cold (2–3°C below the optimal temperature for the chick age). The second group was exposed to moderate heat (2–3°C above the optimal temperature for the age). The third and fourth group were deprived of feed and drinking water for 12 hours and 24 hour, respectively. The fifth chick group was the control group: the birds in this group had optimal environmental conditions and received feed and drinking water immediately upon entering the trial. Ten chicks were taken every day and weighed. Their blood samples were obtained for the assessment of infectious bursal disease virus antibody titres using ELISA method. After that, the birds were sacrificed, their intestinal masses weighed and the quantity of resorbed yolk measured.

The greatest body and intestinal masses were found in the control animals. The body and intestinal masses were the lowest in the group which was denied water and food for 24 hours. The resorption of the yolk sac content was approximately equal in all the chick groups, but the resorption rate varied by days. The highest resorption was observed in the chick groups on the day when feed was denied to them, so that this high resorption could be associated with the bird's body energy requirements. The resorption of the remaining yolk is associated with feed intake: in chicks to which feed is withheld the yolk is resorbed through the yolk sac wall directly into the blood, which increased its usability. When energy requirements are not satisfied, the chick's body probably utilises resorbed antibodies from the yolk remnants, as their glycoprotein composition is suitable for this purpose.

The weight of hatching eggs can influence broiler live performance regardless of hen age. Egg composition is altered with egg weight, but such alterations do not seem to have major effects on broiler growth and processing yields. The chick hatches with a yolk sac which provides nutrients for the transition to independent feeding. Alterations in egg weight and composition do not affect the proportion of yolk sac to body weight as much as its composition, particularly with eggs from very young hens. The contents of the yolk sac are high in fat and protein but very low in carbohydrate, which could lead to ketosis with prolonged fasting. Enhancing the first feed with either carbohydrate or gluconeogenics such as propionic acid may alleviate this ketosis and help early development. The digestive system of the chick is physically complete at hatching but is not fully competent at nutrient retrieval as many enterocytes are orientated to immunoglobulin uptake. Villi length and enzymatic activity increases with feeding, reaching maturity within a few weeks. Access to food and water after hatching varies, and long delays until placement are common. These delays cause losses in live performance. Loss in body weight due to late placement or undernutrition may also affect early muscle development. These adverse effects extend to marketing age and reduced meat yield. Factors that affect early chick development are gaining interest as the length of time to market progressively decreases and the chick's first days represent an increasing proportion of the total time for production.

OBJECTIVE. The purpose of this study was to evaluate the relationship between the yolk sacs separated or not separated by septum and chorionicity twin pregnancies scanned early in the first trimester, and the relation between size and morphologic features of the yolk sac and the outcome of twin pregnancies.

RESULTS. In all 38 sets of twins two yolk sacs were identified. During the first trimester of a dichorionic twin pregnancy, the yolk sacs were always separated by a septum and not separated (“Eight” sign) in monochorionic twin pregnancy. In five cases, one of yolk sac was abnormally large (> 8mm) and had thin wall. Four of the five mothers spontaneously aborted during the next 2-3 weeks. In one case of monochorionic twin ectopic pregnancy two yolk sacs were seen normally.

CONCLUSION. The sonographic identification of yolk sacs in multiple pregnancies allows an early and efficient recognition of presence and chorionicity of twin pregnancy, both in intra – and extrauterine. Identification of abnormal yolk sac or yolk sacs suggests death of one or all embryos.