Jorge Daniel Mikos

Freqüência alimentar e crescimento de alevinos de jundiá, Rhamdia quelen

Silver catfish Rhamdia quelen is an important species commonly found in many Brazilian rivers and other regions of South America. Studies carried out in the last years with this species have pointed its great potential for aquaculture in Brazil, mainly in the Southern States. Feeding frequency is a very important issue for fish producers due to its direct relation to production costs. The present study tested four different feeding frequencies (1, 2, 3, and 4 times a day). Forty jundia fingerlings (1.88g) were stocked in each of the twelve 4m2 tanks (concrete wall and earth bottom) and raised for 65 days. Water temperature ranged from 23 to 27oC during the experimental period and fish from all treatments showed the same growth pattern. Body weight and length, feed conversion rate, and specific growth rate were not significantly different among the treatments. Silver catfish fed only once a day grew similarly to those fed two to four times a day. These findings could optimize farm labor and increase profit in silver catfish production.

Development of the neotropical catfish Rhamdia quelen (Siluriformes, Heptapteridae) incubated in different temperature regimes

The developmental stages for the embryonic and larval periods of the silver catfish (Rhamdia quelen) kept at different temperatures (21, 24, 27 and 30 degrees C) are described. Fish were analysed under light and scanning electron microscopy. For embryonic development, we described 25 stages, which were grouped into seven periods named zygote, cleavage, blastula, gastrula, segmentation, pharyngula and hatching periods. For larval development, we defined three stages (early, mid, and late larvae). Additionally, the main ontogenetic events during the post-larvae and early juvenile periods were also described. This species presents a well developed lateral line and chemosensory systems that grow up during the larval period, maturing in the post-larvae. All tested temperatures are viable to R. quelen development, but a shorter incubation period was necessary to complete the development at lower temperatures. However, some malformations (heart edema) were verified at 30 degrees C.

LIVE AND FORMULATED DIET EVALUATION THROUGH INITIAL GROWTH AND SURVIVAL OF JUNDIÁ LARVAE, Rhamdia quelen

Live diet (LD) dependence and the lack of suitable formulated diets (FD) are major constraints for the expansion of larviculture of many fish species. The low digestibility and nutritional quality of FD are factors that might explain their failure as a stand-alone starter food. To determine whether FD in combination with LD (zooplankton) may efficiently increase larval growth and survival of jundia (Rhamdia quelen), when compared to fish fed by either types of diet alone, jundia larvae (5.57 mm; 1.41 mg) were initially stocked into 12 10-L aquaria (100 larvae per aquarium). Replicate groups (n=4) were fed ad libitum one of the three diets for 20 (when fed FD) or 48 days (when fed LD or the combined diets). Larvae fed FD alone presented significantly lower survival and growth rates as compared to larvae fed LD or a combination of both (co-fed). In addition, co-fed larvae grew better (170 mg) in relation to those fed solely with LD (110 mg). Such better performance of combined feeding indicates that most of the required nutrients are in balance when both diet sources are included. More can be learned about fish larvae nutrition by further testing the effect of feeding combined diets, which include zooplankton, than only testing new ingredients or protein sources commonly used in the elaboration of juvenile or adult fish feeds.

Effect of heat treatment and packaging systems on the stability of fish sausage

The purpose of this study was to evaluate the physicochemical and microbiological stability of sausages produced from mechanically separated fish meat (MSM) obtained from Nile tilapia filleting residues. Different heat treatments (pasteurization or smoking) and packaging systems (conventional or vacuum) were used. The sausages were characterized for chemical composition, weight loss, water activity, instrumental texture and sensorial analysis. Additionally, microbiological analysis, instrumental color, pH, thiobarbituric acid reactive substances (TBARS) and total volatile base nitrogen (TVB-N) were assessed during storage. No presence of Escherichia coli, Salmonella sp. or coagulase-positive Staphylococcus was detected; however, the psychrotrophic count in pasteurized sausages exceeded the limits allowed for consumption. pH and lipid oxidation speed (TBARS) values were reduced when vacuum packaging was used. Volatile nitrogenous bases remained virtually constant during the storage period, and higher values were observed in smoked products. Pasteurized sausages remain stable for 10 and 15 days in conventional and vacuum packages, respectively, and smoked sausages remain stable for 25 and 45 days in conventional and vacuum packages, respectively.