The Egyptian Society for the Development of Fisheries and Human Health (ESDFHH)
Egyptian Journal of Aquatic Biology and Fisheries
1110-6131
2536-9814
16
1
2012
01
01
Distribution of benthic polychaetes populations affected by human activities in the west coast of Alexandria, Mediterranean Sea, Egypt
1
19
EN
Mohamed
El-Komi
National Institute of Oceanography and Fisheries, Alexandria, Egypt
10.21608/ejabf.2012.2107
<br />Marine benthic communities; in particular the soft bottom polychaetes along the western coast of Alexandria, were studied as part of a monitoring program on the effects of human activities on the ecosystem to determine whether discharges from the wastewater outfalls are affecting the surrounding benthos or nat. These communities<br />are used as indicators of sediment and water quality because they can consume or adsorb the pollutants via feeding processes. Data analyses of benthic communities are commonly used to estimate the changes of complexity of the community structure in the stressed area due to one or more of environmental factors. Soft bottom polychaetes in this area were studied using multivariate and biotic indices, measuring abundance and community composition. Possible significant correlations were determined using multi regression analysis with physical, chemical and biological<br />structure. Twenty six polychaete species belonging to 16 families were identified. The benthic polychaete communities in the study area were dominated by two sedentary forms (Capitellidae, Spionidae) and two errantia forms (Nereidae, Syllidae) besides to unidentified Oligochaeta species. These communities were more dominant in the area<br />near outfalls of El Amom drain, El Dekhelah, Nobaria drain and SUMED area, where their frequencies varied among sites and within sites over the study period. Shannon’s index (H') varied spatially from 0.49 to 1.76, Margalef richness index (d) from 0.17 to 1.58, and evenness index (J) from 0.44 to 0.79, indicating poor polychaete diversity.<br />High diversity may be attributed to the presence of oppertunitistic species, which are tolerant to high organic matter and chemical residues. The relative frequency of abundant polychaetes can be ranked as follows: Capitella (15.4%) > Oligochaeta (14.9%) > Polydora (14.4%) > Prionospio (11%) > Nereis (10.6%) > Syllis (5.4%).<br />Sedentary polychaetes (Capitellida capitata, Polydora caeca, Prionospio cirrifera) and an errant form (Nereis irrorata) were regularly distributed within stations but their abundance varied between stations. The highest density of species and<br />specimens were recorded at stations 2, 4, 5, 7, 8, and 11, where the tendency of abundance increased from May to July reaching 1092 to 1385 ind./m2. The increase in polychaete abundance observed in outfall area could be due to the effect of trophic level.
Polychaetes,human activity,biodiversity,trophic level
https://ejabf.journals.ekb.eg/article_2107.html
https://ejabf.journals.ekb.eg/article_2107_352b9b7010e2eebbf4402fb09f5d4eed.pdf
The Egyptian Society for the Development of Fisheries and Human Health (ESDFHH)
Egyptian Journal of Aquatic Biology and Fisheries
1110-6131
2536-9814
16
1
2012
01
01
Effect of spawning month, dietary protein and pond protection on fry production of the Nile tilapia, Oreochromis niloticus
21
32
EN
Magdy
Soltan
Faculty of Agriculture, Benha University
magdyasoltan@yahoo.com
Saeed
El-Laithy
Department of Hygiene, Animal Behavior and Management. Fac. Veterenary Medicine,
Benha University, Egypt
Gamal
El-Nagaar
World Fish Center, Abbassa, Abou Hammad, Sharkia, Egypt
Waheed
Mohammed
World Fish Center, Abbassa, Abou Hammad, Sharkia, Egypt
10.21608/ejabf.2012.2108
The practical work of the present experiments was carried out at the World Fish<br />Center, Abbassa, Abou Hammad, Sharkia, Egypt. The experiment aimed to<br />investigate the effect of spawning month (April and May), dietary protein level (25 or<br />35%) and protection of spawning tanks (covering or uncovering of the spawning<br />tanks) on fry production and average fry weight of the Nile tilapia. The obtained<br />results can be summarized as follow:<br />- Fry production/tank were found to be 6462 and 19082/tank during the two months<br />April and May, 10719 and 14824/tank for the two dietary protein levels, 25 and<br />35% and 16428 and 9115 fry/tank for the covered and uncovered tanks,<br />respectively and the differences in fry production due to the effect of spawning<br />month, dietary protein content and tank protection were significant.<br />- Averages of individual fry weight as affected by month, dietary protein levels and<br />pond protection were found to be 0.025 and 0.016 g during the two months April<br />and May, 0.021 and 0.019 g for the two dietary protein levels, 25 and 35% and<br />0.018 and 0.023 g for the covered and uncovered tanks, respectively. Spawning<br />month and tank protection significantly affected individual fry weight while<br />dietary protein levels had no significant effect on fry weight.<br />- The interaction between the studied factors affected individual fry weight of the Nile<br />tilapia indicated that the highest average individual fry weight was recorded for fish<br />group raised in covered tanks and received the lower protein content during April.<br />On the other hand, the lowest average individual fry weight was recorded for<br />broodfish raised in an uncovered tanks and received the higher protein level (35%)<br />in May.
Nile tilapia,Oreochromis niloticus,Spawning,protein,protection
https://ejabf.journals.ekb.eg/article_2108.html
https://ejabf.journals.ekb.eg/article_2108_dcf8d5ede4f68cc90f72330b768180ab.pdf
The Egyptian Society for the Development of Fisheries and Human Health (ESDFHH)
Egyptian Journal of Aquatic Biology and Fisheries
1110-6131
2536-9814
16
1
2012
01
01
Distribution of benthic communities affected by human activities in the west coast of Alexandria, Mediterranean Sea, Egypt
41
59
EN
Mohamed
El-Komi
National Institute of Oceanography and Fisheries, Alexandria, Egypt
10.21608/ejabf.2012.2110
In the framework of marine ecosystem evaluation, this study was carried out where sediment microorganisms were collected bimonthly from 16 sites over one year in the western coast of Alexandria. This area comprises different human activities (urban sewage, agriculture irrigation, industrial wastes, petroleum spill, tourist stress, fishing and commercial navigation). Macrobenthos communities are well indicators of water and sediment quality. Bottom invertebrate’s diversity, comparison of benthos communities at different sampling sites and the biomass were determined as well as<br />the numerical abundance of benthos in comparison to the different environmental parameters. Discharging of chemical pollutants in coastal waters leads to significant degradation in the water quality that altered the macro invertebrates’ diversity indices. The most western sites are less stressed area indicating low diversity rather than the<br />stressed area close to the main sources of pollutants discharge that has relatively high pollution and generally with good diversity. The benthic communities are dominated by few species of pollution tolerance which are used as indicators of polluted sediments such as free-living nematodes and polychaetes. The regional distribution of<br />benthic invertebrate’s communities varied at different sites and over the period of collections that total abundance ranged from 959 to 8444 ind./m2 with an annual average of 3072 ind./m2 and seven benthos groups can be sequenced as follows: Nematodes 46% > polychaetes 22% > amphipods 13.8% >cirripedes 4.8% > oligochaetes 4% > gastropods 3.0% > bivalves 1.5%. On the other hand, biomass of benthic structure has an annual average of 155 g/m2, where six predomination benthic groups can be ranked in the following sequence: Cirripedes 33.5% > Algae 30.6% > Gastropods 12.7% > Bivalves 9.1% > Sea grass 7.0% > Polychaetes 1.7%. At the different sites, the general structure of species number of benthos groups indicated that Polychaeta was the most common group comprising 27 species of 80<br />the total number of taxa. The values of species diversity (H`) had relatively moderate diversity (1.3 – 2.02) at most stations and in general the decline in diversity is primarily attributed to the uneven distribution of individuals among the species. On the other hand, the species diversity was only 1.6 at Site 2 though it was the richest<br />that may be attributed to the number of species. Values of the evenness index indicated that sites 1, 8, 9, 10 were highly diverse in benthic communities. The Swartz’s dominance index value indicated less stress with high diversity and number of species. The area located close to the outfall of the two main drains are characterized by having distinct eutrophication level leading to significant increase in the species richness and mean abundance of benthic communities of the tolerant species. Continuous monitoring and assessing of macrobenthic communities is needed to determine the short and long-term changes in the marine ecosystem that are essential for fisheries management along the coastal region.
macro benthos,impact of pollution,biodiversity,benthic communities,Polychaetes,bivalves,Crustaceans
https://ejabf.journals.ekb.eg/article_2110.html
https://ejabf.journals.ekb.eg/article_2110_4c01e21dbdef8a01d4fc91e215818db5.pdf
The Egyptian Society for the Development of Fisheries and Human Health (ESDFHH)
Egyptian Journal of Aquatic Biology and Fisheries
1110-6131
2536-9814
16
1
2012
01
01
Impact of some environmental factors on distribution of certain vector snails in five Egyptian Governorates
33
40
EN
Abd El-Halim
Saad
Zoology Department, Faculty of Science, Ain Shams University
Bayaumy
Mostafa
Environmental Research Department.
Ahmed
Azzam
Environmental Research Department.
Samah
El-Magd
Clinical Microbiology Department, Theoder Bilharz Research Institute, P.O. Box 30
Imbaba, Giza, Egypt.
10.21608/ejabf.2012.2111
The present study showed that the distribution of the intermediate host snails of Fasciola sp. and Schistosoma sp. varied among the five surveyed Egyptian governorates. It was found that the ratios of distribution of Lymnaea natalensis,<br />Bulinus truncatus and Biomphalaria alexandrina snails of the total surveyed sites were 44.1%, 26.9% and 4.9% respectively. Moreover, infected L. natalensis, B. truncatus and B. alexandrina snails in these sites were 1.96%, 3.4% and 0.98% respectively. However, infected L. natalensis and B. truncatus were found in Damietta and Beheira, while infected B. alexandrina were found only in Giza. Springwas the highest season in percentage of collected snails (38.9%), while summer was the lowest one (8.8%). L. natalensis, B. truncatus and B. alexandrina showed high distribution in Ismailia, Damietta and Giza governorates as represented by 4.16, 4.38 and 0.51 snails/site respectively. Some environmental factors were found affecting the distribution of snails. The means of pH and temperature in positive sites for vector snails were 6.8 and 26.7°C respectively. L. natalensis, B. truncatus appeared in water<br />of electric conductivity mean of 415.5 μ.mhos/cm and 284.5 ppm of mean total dissolved salts, while B. alexandrina was found at 481 μ.mhos/cm and 603 ppm respectively.
Fasciola sp,Schistosoma sp,Lymnaea natalensis,Bulinus truncatus,Biomphalaria,alexandrina,Distribution
https://ejabf.journals.ekb.eg/article_2111.html
https://ejabf.journals.ekb.eg/article_2111_5d216b3d0c664a68c2ecbffdda1d16f0.pdf
The Egyptian Society for the Development of Fisheries and Human Health (ESDFHH)
Egyptian Journal of Aquatic Biology and Fisheries
1110-6131
2536-9814
16
1
2012
01
01
Larval development of two atherinid fish species from the Red Sea, Egypt
61
71
EN
Mohamed
Abu El-Regal
Marine science department, Faculty of Science, Port Said University, Egypt
10.21608/ejabf.2012.2112
Larvae of the family Atherinidae were collected throughout a period of 15 years from different areas in the Gulf of Aqaba and Red Sea proper from Hurghada to Shalteen by plankton nets of 500μm. Atherinid larvae were identified by using<br />different identification guides. Larvae were illustrated by camera lucida and photographed by Nikon camera fixed on an Olympus microscope XZ. The morphometrics and sizes of all collected larvae were measured using an eye-piece<br />micrometer. Very large number of larvae were collected and used for the description of all developmental stages. The smallest size of Atherinomorus lacunosus was 5 mm and the largest size was 20 mm. whereas the smallest size of Hypoatherina temmincki was 3mm and the largest was 5mm.
Fish larvae,Atherinidae,Red Sea,Aqaba Gulf
https://ejabf.journals.ekb.eg/article_2112.html
https://ejabf.journals.ekb.eg/article_2112_31a62acd33878b7553e7d5c1578c7137.pdf
The Egyptian Society for the Development of Fisheries and Human Health (ESDFHH)
Egyptian Journal of Aquatic Biology and Fisheries
1110-6131
2536-9814
16
1
2012
01
01
Interaction of the mormyrid fish Mormyrus kannume (Forsskål, 1775) reproduction and feeding intensity with the environment in a Nile Delta Canal,Egypt
73
94
EN
Elsayed
Khallaf
0000-0003-1035-2280
Zoology Department, Faculty of Science, Minufiya University,
Shebeen Alkoom, Egypt
ekhallaf@yahoo.com
Mohammad
Authman
Hydrobiology Department, National Research Centre, Dokki 12622, Giza, Egypt
10.21608/ejabf.2012.2113
The effect of environmental factors on the fish biological parameters and their quantification was investigated in this study during the period from January 2005 to January 2006. Bahr Shebeen Canal is a Nile canal that represents a fishery resource in the Delta of Egypt, where Mormyrus kannume shows a scanty abundance. During the period from of June to September, there was a chance to examine such interaction. The obtained results revealed that the fish spawn over an extended period, from November till May, with two main peaks of spawning activity namely: November-<br />December and February-April. Consequently, the gonadosomatic index (GSI) could not be correlated significantly with variation in either temperature or photoperiod. In those periods of spawning activity, the fish showed the lowest feeding intensity; i.e., low abundance. This was also quantified mathematically by significant correlations between the seasonal average (excluding winter) of stomachsomatic index (SSI) and either average daily temperature (T) and photoperiod (PP) for females and to a lower extent with males. These relationships were negatively correlated, and more<br />significant among females than males, that was attributed to a higher activity of feeding among females. Also, the fish reproduction and feeding activities were correlated significantly with electrical conductivity and rainfall. This indicated that<br />the fish are subject to the effect of associated environmental parameters interacting with their biology. The susceptibility of this fish species to change in those variables indicates its vulnerability to any adverse climatic change.<br />The relationship between each of fecundity, egg diameter and gonadosomatic index and the female length or age were also examined and discussed, and the mathematical correlations were presented.
Mormyrus kannume,environmental effects,Reproduction,feeding,Ecology,aquatic biology
https://ejabf.journals.ekb.eg/article_2113.html
https://ejabf.journals.ekb.eg/article_2113_cfebfa6946d97d5a15fa69a91b4c3a3c.pdf
The Egyptian Society for the Development of Fisheries and Human Health (ESDFHH)
Egyptian Journal of Aquatic Biology and Fisheries
1110-6131
2536-9814
16
1
2012
01
01
Reproductive biology of the tub gurnard Trigla lucerna (linnaeus, 1758), in the Libyan eastern coast of Mediterranean Sea.
95
104
EN
Ashraf
Ahamed
Marine Science Department, Faculty of Science, Suez Canal University, Ismailia –
Egypt
10.21608/ejabf.2012.2115
The reproductive biology of Trigla lucerna, (family: Triglidae) inhabiting Libyan eastern coast was studied during the period from January to December 2007. There were monthly variation in sex ratio, and a tendency for more females (731 fish, 52.2%) than males (669 fish, 47.8%) for the collected population. Overall sex ratio was 1: 1.09 for males to females. The male of Trigla lucerna attained its first maturity at the total length of 13.9 cm, while the first sexual maturity of female was attained at 15.3 cm. The gonado-somatic indices of males were lower than that of females. Males and females have a definite breeding season which extends from January till March. An increase in oocyte diameter was evident in November (with an average of 225 μ) and this increase continued in the following months till March, with an average value of 498μ. The absolute fecunncldity ranged from 678 to 10047 eggs for fish length<br />ranging from 13.5 to 22.6 cm. Also, the fecundity increased from 755 to 10055 eggs with the increase of weight from 16.7 to 108.2 g.
Triglidae,Trigla lucerna,Reproductive biology,Mediterranean Sea,Libyan eastern coast
https://ejabf.journals.ekb.eg/article_2115.html
https://ejabf.journals.ekb.eg/article_2115_469e99f3f6dc25d6719781843e249eda.pdf
The Egyptian Society for the Development of Fisheries and Human Health (ESDFHH)
Egyptian Journal of Aquatic Biology and Fisheries
1110-6131
2536-9814
16
1
2012
01
01
Effect of dried earth worm (Aporrectodea caliginosa) as replacement of fish meal on growth and survival rate of the freshwater prawn, Macrobrachioum rosenbergii (DE MAN 1879) larvae.
105
114
EN
Madlen
Habashy
National Institute of Oceanography and Fisheries, El-Qanater El-Khayria, Egypt
10.21608/ejabf.2012.2116
An experiment was conducted to evaluate the potential of earthworm powder in replacement of the high cost fish meal for feeding the freshwater prawn, Macrobrachium rosenbergii. Triplicate groups of prawns were fed on control diet<br />(fish meal based protein) or experimental diets in which earthworm meal was used to replace fish meal as animal protein source at various inclusion levels namely 0% (control), 25, 50, 75 and 100%. The diets were coded EM1 (control) to EM5. The highest growth performance in term of length, weight and SGR were observed in prawn fed on EM2. The lowest and best feed conversion ratio, 1.1 was recorded with diet containing 25% earthworm meal (EM2). Highest survival (93.5%) was observed within the prawn group fed on the same diet. Biochemical composition of prawn carcasses showed no significant differences among different diets, while the higher level of protein was found in prawn fed on EM2. Results revealed that 25% earthworm meal is recommended in the diet of M. rosenbergii as replacement of fish<br />meal.
earthworm,feeding,Macrobrachium rosenbergii,proximate composition
https://ejabf.journals.ekb.eg/article_2116.html
https://ejabf.journals.ekb.eg/article_2116_537c24d45b1aa913cde249b8aaf3c787.pdf
The Egyptian Society for the Development of Fisheries and Human Health (ESDFHH)
Egyptian Journal of Aquatic Biology and Fisheries
1110-6131
2536-9814
16
1
2012
01
01
Reproductive biology of the seahorse Hippocampus fuscus (teleostei: syngnathidae), in the Suez Canal, Egypt.
115
131
EN
Ashraf
Ahmed
Marine Science Department, Faculty of Science, Suez Canal University, Ismailia, Egypt.
Howaida
Gabr
Marine Science Department, Faculty of Science, Suez Canal University, Ismailia, Egypt.
Ola
Khawasek
Marine Science Department, Faculty of Science, Suez Canal University, Ismailia, Egypt
10.21608/ejabf.2012.2117
The reproductive biology of the drab seahorse, Hippocampus fuscus was investigated at two sites (Great Bitter Lakes and Lake Timsah) in the Suez Canal, Egypt, to determine sex ratio, reproductive maturity stages, gonad index, spawning<br />season, and male/female fecundity. A total of 393 seahorses were collected from Great Bitter Lakes and 319 from Lake Timsah from August 2006 to July 2007. Male to female ratios did not depart significantly from a 1:1 ratio, either through the whole study period or between the seasons. Female seahorses progressed through three ovarian maturity<br />stages during the reproductive cycle: Previtellogenic ovaries, Vitellogenic ovaries, and Mature ovaries. Hippocampus fuscus appears to undergo year-round reproduction in the Suez Canal, as reproductively mature females and brooding males with eggs/embryos in the brood pouch were captured every month of the year, although most mature<br />specimens were collected in mid winter–early summer. The peak of female gonadosomatic index (GSI) coincided with the peak occurrence of mature ovaries in female seahorses. Vitellogenesis in female seahorses appears to be asynchronous. Female H.fuscus were relatively more fecund in Lake Timsah than in Great Bitter Lake; where fecundity ranged from 160 to 686 ova in Lake Timsah and from 86 to 372 ova in Great Bitter Lake. At both sites, female fecundity was positively correlated with seahorse height, total weight, and gonad weight. Male H. fuscus was also relatively more fecund<br />(number of eggs and/or embryos in the brood pouch). Male fecundity was positively correlated to seahorse height. Female H. fuscus appeared to have higher fecundity than males in the sampled populations (i.e., mean number of ripe ova or clutch size exceeds the mean brood number). This study is so far the first to document aspects of the<br />reproductive biology of H. fuscus in the Suez Canal and adds to our knowledge of this relatively poorly studied seahorse species.
Hippocampus fuscus,Reproductive biology,Suez Canal,Egypt
https://ejabf.journals.ekb.eg/article_2117.html
https://ejabf.journals.ekb.eg/article_2117_b28ad30bbf5280317cebc4f21e3c6058.pdf
The Egyptian Society for the Development of Fisheries and Human Health (ESDFHH)
Egyptian Journal of Aquatic Biology and Fisheries
1110-6131
2536-9814
16
1
2012
01
01
Epibiont communities of the two spider crabs Schizophrys aspera (H. Milne Edwards,1834) and Hyastenus hilgendorfi (De Man, 1887) in Great Bitter Lakes, Suez Canal,Egypt.
133
144
EN
Nesreen
Ibrahim
Marine Science Department, Faculty of Science, Suez Canal University, Ismailia, Egypt
10.21608/ejabf.2012.2118
The epibiont communities of the two spider crabs Schizophrys aspera and Hyastenus hilgendorfi in Great Bitter Lakes were studied during spring and summer of 2011. A sum of six taxa including twelve species of epibionts was recorded on each of the two investigated crabs. Most of the epibionts were including Protozoa, Hydrozoa, Polychaeta, Cirripedia, Bryozoa and tunicates. Generally, Cirripedia and Polychaeta dominated the other epibiont species on the two investigated spider crabs. Barnacles were the most widespread species on the four examined parts of Schizophrys aspera, whereas the abdomen of Hyastenus hilgendorfi was commonly covered with polychaetes, followed by barnacles while tunicates were dominating on mouth parts, carapace and limbs. Abundance of epibionts increased as the crab size increased.
Spider crab,epibiont,Bitter Lakes,Suez Canal
https://ejabf.journals.ekb.eg/article_2118.html
https://ejabf.journals.ekb.eg/article_2118_5d949bc1f02d9773363923f26d06a934.pdf
The Egyptian Society for the Development of Fisheries and Human Health (ESDFHH)
Egyptian Journal of Aquatic Biology and Fisheries
1110-6131
2536-9814
16
1
2012
01
01
Effect of chelating agent edta (ethylene diamine tetra acetic acid, disodium salt) as feed additive on controlling heavy metals residues in Sarotherodon galilaeus fish
145
156
EN
Hayam
Tonsy
Animal Production Research Institute, By–product utilization Dept., ARC, Dokki, Giza,
Egypt.
Abeer
Abdel-Rahman
Animal Health Research Institute, Biochemistry Dept., ARC, Dokki, Giza, Egypt.
10.21608/ejabf.2012.2119
The study was undertaken in order to determine the effect of chelating agent EDTA as feed additive on controlling heavy metals (Pb&Cd) which cause some dangerous diseases and its impact on growth performance, feed and protein<br />utilization, carcass composition and biochemical parameters in mono sex Galilee Tilapia fingerlings were studied. Galilee tilapia fingerlings were collected from El-Zaheria village, Abo- Hamad,Sharkia (recorded as polluted area) and analyzed for lead, cadmium and zinc contamination at the start of experiment. The fish were divided into 5 treatments<br />EDTA (ethylene diamine tetra acetic acid, disodium salt) were included in the diets ata rate of 0.0, 0.5, 1.0, 1.5 and 2.0%. The diets were formulated to be iso-nitrogenous (30.19%±0.15 crude protein) and iso-caloric (4459.49± 85 kcal gross energy/kg diet). After that, the fish were randomly distributed into 15 aquarium (5 fish/aquaria) of<br />Galilee Tilapia fingerlings, Each diet treatment was applied to triplicate groups (54.2± 0.99 g/fish) at rate six days of the week and the experiment extended for 49 days. The obtained results showed that, lead (Pb) and cadmium (Cd) concentrations were significantly decreased in all EDTA treatments in the whole body and fish flesh<br />of Galilee Tilapia fingerlings compared with those at the start of the experiment and control group (E1, 0.0% EDTA) .<br />The biochemical parameters were significantly improved at (P< 0.05). The uric acid and cholesterol levels were significantly decreased. The highest weight gain (WG), average daily gain (ADG), and specific growth weight (SGR) and protein and nutrient utilization at (P< 0.05) were recorded by E4 (1.5% EDTA) followed by E3 (1.0% EDTA), respectively. In conclusion the addition of EDTA to contaminated fish with heavy metals, reduced significantly Pb and Cd levels. The obtained results showed that all the tested biochemical parameters and growth performance, protein, nutrient utilization body carcass were improved due to EDTA application and the effects were more pronounced at 1.5% EDTA/ kg diet, which are considered as the optimum dose that improve the healthy status and growth parameters of fish in this experiment.
EDTA,heavy metals Galilee Tilapia fingerlings,Growth performance,feed utilization,biochemical parameters
https://ejabf.journals.ekb.eg/article_2119.html
https://ejabf.journals.ekb.eg/article_2119_738a4f3feabebd7fa1cfef8164303f0e.pdf