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  In the present study, mycobiota and natural occurrence of aflatoxin B₁ (AFB₁) in pellet feed and feed ingredients used in a feed manufacturing plant for rainbow trout nutrition was investigated. The samples were cultured on the standard isolation media for 2 weeks at 28 ºC. Identification of fungal isolates was implemented based on the macro- and microscopic morphological criteria. AFB₁ was detected using high performance liquid chromatography (HPLC). Based on the results obtained, a total of 109 fungal isolates were identified of which Aspergillus was the prominent genus (57.0%), followed by Penicillium (12.84%), Absidia (11.01%) and Pseudallscheria (10.10%). The most frequent Aspergillus species was A. flavus (60.66%) isolated from all feed ingredients as well as pellet feed. Among 37 A. flavus isolates, 19 (51.35%) were able to produce AFB₁ on YES broth in the range of 10.2 to 612.8 µg/g fungal dry weight. HPLC analysis of trout feed showed that pellet feed and all feed ingredients tested except gluten were contaminated with different levels of AFB₁ in the range of 1.83 to 67.35 µg/kg. Unacceptable levels of AFB₁ were reported for feed including soybean, fish meal and wheat. These results indicate the importance of AF contamination of trout feed in amounts higher than the acceptable level as a risk factor for fish farming production.

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The Persian Gulf is of great economical, environmental and political importance, and includes around 205 species of fishes that only some of them have been studied parasitologically. From the order Pleuronectiformes ( ray-finned fishes), Psettodes erumei (Psettodidae), Pseudorhombus elevatus (Bothidae) and Brachirus orientalis (Soleidae) were selected for the survey. One hundred and forty eight fishes including 97 P. erumei, 43 P. elevatus and 8 B. orientalis were provided from two different regions of Iranian waters of the Persian Gulf and Oman Sea. From P. erumei, 4 species of nematodes, one cestode and one acanthocephal species are reported including: Philometra sp., Contracaecum sp., Pseudoterranova sp., Raphidascaris sp., Dasyrhynchus sp. (Trypanorhyncha) larvae and Serrasentis sagittifer. This is the first report of S. sagittifer in P. erumei from the Persian Gulf. P. elevatus had fewer species of parasites including one nematode, Contracaecum, one copepod, Heterochondria pillai and one digenea metacercaria Stephanostomum sp. Brachirus orientalis harbored one copepod and two digenea species, Allocreadium sp. and Lepocreadioides zebrini. Our research provides evidences that Indian spiny turbots have larger diversity of parasites than the deep flounders.

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Folic acid (FA) is an essential water-soluble vitamin, that is unstable in environmental condition and does not regard in vitamin premixes in spite of its importance. In this study 270 beluga sturgeon fingerlings with weight of 5-8 g were fed by various levels of FA: 0.6 (Control/treatment 1), 2.68 (treatment 2), 3.72 (treatment 3), 4.84 (treatment 4) mg kg^-1 feed with three replications for 56 days. Effect of treatment groups on growth, hematological, biochemical parameters before and after stress and opercular respiratory rate (ORR) during stress was investigated in fish fingerlings. The results showed the treatments has significant differences on FCR, SGR, feed efficiency and weight gain (p<0.05). the treatments has significant differences with the control group on red blood cells (RBC) count, hemoglobin (Hb) and Hct (P<0.05). Before stress, cortisol and glucose levels among treatment groups had no significant differences, but after stress they had. Minimum and maximum responses in cortisol levels were observed in treatment two (427.92±6.05 ng mL^-1) and control groups (830.32±5.97 ng mL^-1), respectively. Minimum glucose levels (43.75±1.49 ng mL^-1) in control group and the maximum in treatment two (58.25±1.49 ng mL^-1) were observed.There were significant differences for ORR in 0-5, 5-10, 10-20, 30-40 minutes during oxygen challenge among treatment groups (p<0.05). But this indicator in 20-30 minutes was not affected by treatments. The results of this study, showed that the fish with FA 3.72 mg kg^-1 diet have more resistance against environmental oxygen challenge, therefor can be stated FA may lessen the negative effects of stress in beluga sturgeon fingerling.